Bio

Bio


Kathryn Barton attended elementary school in Oak Park, Ill and grades 6 through high school (Humanistiska Linjen) in Göteborg and Mölndal, Sweden. In 1978 she returned to the United States to attend college at the University of Wisconsin-Madison. She was inspired to study genetics and developmental biology by undergraduate coursework she took at the UW. In particular the Biocore curriculum, a two-year, in depth survey course, was influential. In addition to offering excellent lectures by faculty experts, this course afforded her the opportunity to pursue an independent laboratory project in William Engels’ lab in the Department of Genetics. Her project was to estimate the rate of new P element insertion on the X chromosome in a hybrid dysgenic Drosophila. Other undergraduate lab work included dishwashing in a Department of Plant Pathology lab and fieldwork for maize geneticist Jerry Kermicle. She received her B.S. in Molecular Biology in 1983.

She did graduate research in Dr. Judith Kimble’s lab, also at the University of Wisconsin. There, she worked to understand how hermaphrodites of the nematode worm C. elegans make two kinds of germ cells, sperm and eggs. This work helped identify three genes - FEM3, FOG1 and GLD1 - that direct germ cells down either a sperm or an oocyte pathway of development. She received her Ph.D. in Genetics in 1989.

In 1989, she began postdoctoral work in plant biology in Dr. Scott Poethig’s lab at the University of Pennsylvania. There she isolated Arabidopsis mutants – SHOOTMERISTEMLESS, TOPLESS and PINHEAD/AGO10 - with defects in the shoot apical meristem. Among these were mutants that entirely lacked a shoot apical meristem but had near normal cotyledons. This established that it was possible to separate the process of cotyledon formation from shoot apical meristem formation. It also established the SHOOTMERISTEMLESS gene as a factor specifically required for shoot apical meristem formation in the embryo. She left the University of Pennsylvania in 1992 to return to the Department of Genetics at the University of Wisconsin – Madison as a faculty member.

As an assistant, and later associate, professor she continued work on shoot apical meristem and embryo development. Her lab cloned the SHOOTMERISTEMLESS gene and showed it to be a KNOTTED like transcription factor. This cemented the understanding of the role of KNOTTED like factors in meristem formation and maintenance. Mutations in the BOBBER gene (later shown to encode a heat shock factor) were shown to limit the extent of SHOOTMERISTEMLESS RNA expression to meristematic cells. Her lab also identified a novel dominant mutation (called phabulosa-1d) affecting leaf polarity and showed this to be due to a mutation in a member of the plant HomeoDomain Leucine Zipper gene family. Besides being important in understanding the establishment of leaf polarity, these mutations were later useful in establishing the role of small RNAs in leaf development.

She became affiliated with Stanford Biology in 2001 when her lab moved to the Carnegie Institution’s Department of Plant Biology (located on the Stanford campus).. There, her lab continues to study the genetic control of shoot apical meristem function and the establishment of leaf polarity using molecular genetics. (See Research Description for details.)

She pursues teaching in a variety of formats. At Carnegie DPB she has helped run the Summer Intern Research Program for students interested in trying their hand at plant research. (Interested students should see the link at https://dpb.carnegiescience.edu/education/summer-internship-program). She teaches a freshman seminar on Hunger at Stanford. She guest lectures at area high schools. She writes a blog called Vanishing Bananas (www.vanishingbananas.blogspot.com) on various fun observations made on plants inside and outside the lab.

Academic Appointments


Boards, Advisory Committees, Professional Organizations


  • Board Member, Scientific Advisory Board, Max Planck Institute for Plant Breeding Research (2014 - Present)
  • Board Member, International Plant Molecular Biology Board (2013 - Present)
  • Standing Member, Molecular Genetics B Study Section, NIH (2012 - Present)

Professional Education


  • B.S., University of Wisconsin-Madison, Molecular Biology (1983)
  • Ph.D., University of Wisconsin-Madison, Genetics (1989)

Research & Scholarship

Current Research and Scholarly Interests


Plants make new leaves and stems from clusters of undifferentiated cells located at the tips of branches. These cell clusters are called apical meristems. We study transcription factors that control growth and development of apical meristems. Our studies include plants growing in environments rich in water and nutrients as well as in poor environments. The deeper knowledge of plant development gained from these studies will ultimately help increase food security in a changing environment.

Teaching

2013-14 Courses


Graduate and Fellowship Programs


  • Biology (School of Humanities and Sciences) (Phd Program)

Publications

Journal Articles


  • Arabidopsis KANADI1 acts as a transcriptional repressor by interacting with a specific cis-element and regulates auxin biosynthesis, transport and signaling in opposition to HD-ZIPIII factors. Plant Cell Huang, T., Harrar, Y., Lin, C., Reinhart, B., Newell, N. R., Talavera-Rauh, F., Hokin, S. A., Barton, M. K., Kerstetter, R. A. 2014; in press
  • Establishing a Framework for the Ad/abaxial Regulatory Network of Arabidopsis - Ascertaining Targets of HD-ZIPIII and KANADI Regulation Plant Cell Reinhart, B. J., Liu, T., Newell, N. R., Magnani, E., Huang, T., Kerstetter, R. A., Michaels, S., Barton, M. K. 2013; 25 (9): 3228-3249

    View details for DOI 10.1105/tpc.113.111518

  • Brassinosteroids regulate organ boundary formation in the shoot apical meristem of Arabidopsis PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Gendron, J. M., Liu, J., Fan, M., Bai, M., Wenkel, S., Springer, P. S., Barton, M. K., Wang, Z. 2012; 109 (51): 21152-21157

    Abstract

    Spatiotemporal control of the formation of organ primordia and organ boundaries from the stem cell niche in the shoot apical meristem (SAM) determines the patterning and architecture of plants, but the underlying signaling mechanisms remain poorly understood. Here we show that brassinosteroids (BRs) play a key role in organ boundary formation by repressing organ boundary identity genes. BR-hypersensitive mutants display organ-fusion phenotypes, whereas BR-insensitive mutants show enhanced organ boundaries. The BR-activated transcription factor BZR1 directly represses the cup-shaped cotyledon (CUC) family of organ boundary identity genes. In WT plants, BZR1 accumulates at high levels in the nuclei of central meristem and organ primordia but at a low level in organ boundary cells to allow CUC gene expression. Activation of BR signaling represses CUC gene expression and causes organ fusion phenotypes. This study uncovers a role for BR in the spatiotemporal control of organ boundary formation and morphogenesis in the SAM.

    View details for DOI 10.1073/pnas.1210799110

    View details for Web of Science ID 000313123700080

    View details for PubMedID 23213257

  • Plan B for Stimulating Stem Cell Division PLOS GENETICS Barton, M. K. 2012; 8 (11)

    View details for DOI 10.1371/journal.pgen.1003117

    View details for Web of Science ID 000311891600078

    View details for PubMedID 23173006

  • Genome-wide binding-site analysis of REVOLUTA reveals a link between leaf patterning and light-mediated growth responses PLANT JOURNAL Brandt, R., Salla-Martret, M., Bou-Torrent, J., Musielak, T., Stahl, M., Lanz, C., Ott, F., Schmid, M., Greb, T., Schwarz, M., Choi, S., Barton, M. K., Reinhart, B. J., Liu, T., Quint, M., Palauqui, J., Martinez-Garcia, J. F., Wenkel, S. 2012; 72 (1): 31-42

    Abstract

    Unlike the situation in animals, the final morphology of the plant body is highly modulated by the environment. During Arabidopsis development, intrinsic factors provide the framework for basic patterning processes. CLASS III HOMEODOMAIN LEUCINE ZIPPER (HD-ZIPIII) transcription factors are involved in embryo, shoot and root patterning. During vegetative growth HD-ZIPIII proteins control several polarity set-up processes such as in leaves and the vascular system. We have identified several direct target genes of the HD-ZIPIII transcription factor REVOLUTA (REV) using a chromatin immunoprecipitation/DNA sequencing (ChIP-Seq) approach. This analysis revealed that REV acts upstream of auxin biosynthesis and affects directly the expression of several class II HD-ZIP transcription factors that have been shown to act in the shade-avoidance response pathway. We show that, as well as involvement in basic patterning, HD-ZIPIII transcription factors have a critical role in the control of the elongation growth that is induced when plants experience shade. Leaf polarity is established by the opposed actions of HD-ZIPIII and KANADI transcription factors. Finally, our study reveals that the module that consists of HD-ZIPIII/KANADI transcription factors controls shade growth antagonistically and that this antagonism is manifested in the opposed regulation of shared target genes.

    View details for DOI 10.1111/j.1365-313X.2012.05049.x

    View details for Web of Science ID 000309064100003

    View details for PubMedID 22578006

  • Of Blades and Branches: Understanding and Expanding the Arabidopsis Ad/abaxial Network Through Target Identification Cold Spring Harbor Symposia On Quantitative Biology Liu, T., Reinhart, B. J., Magnani, E., Huang, T., Kerstetter, R. A., Barton, M. K. 2012; 77 (1): 31-45
  • A Per-ARNT-Sim-Like Sensor Domain Uniquely Regulates the Activity of the Homeodomain Leucine Zipper Transcription Factor REVOLUTA in Arabidopsis PLANT CELL Magnani, E., Barton, M. K. 2011; 23 (2): 567-582

    Abstract

    Class III homeodomain leucine zipper (HD-ZIP III) transcription factors regulate critical developmental programs in plants; these include leaf polarity, polarity along the shoot-root axis, and stem cell specification and proliferation. One of the defining features of HD-ZIP III proteins is the presence of a Per-ARNT-Sim-like (PAS-like) MEKHLA domain at the C terminus. PAS-like domains are known to respond to a variety of chemical and physical stimuli. Here, we provide evidence that the MEKHLA domain acts as a negative regulator of Arabidopsis thaliana HD-ZIP III REVOLUTA activity. Based on experiments in yeast and plants, we propose a model in which the MEKHLA domain inhibits dimerization through a sequence-independent steric masking mechanism. This inhibition is relieved in response to a cellular signal that requires the C terminus of the MEKHLA domain for its perception. Overexpression experiments suggest that this signal is unequally distributed and/or sensed in the plant. Our data show that the function of the REVOLUTA MEKHLA domain differs among other HD-ZIP III family members; this difference may explain the genetic differences that have been observed among family members. This finding, combined with our phylogenetic analysis, suggests that REVOLUTA is the latest type of HD-ZIP III protein to have evolved in land plants.

    View details for DOI 10.1105/tpc.110.080754

    View details for Web of Science ID 000288801000012

    View details for PubMedID 21357492

  • Twenty years on: The inner workings of the shoot apical meristem, a developmental dynamo DEVELOPMENTAL BIOLOGY Barton, M. K. 2010; 341 (1): 95-113

    Abstract

    The shoot apical meristem of angiosperm plants generates leaf, stem and floral structures throughout the plant's lifetime. To do this, the plant must maintain a population of stem cells within the meristem while at the same time carefully controlling the placement and establishment of new leaf primordia. As there is little cell rearrangement in plants, underlying patterning mechanisms must exert careful control of cell division rates and orientations to achieve the correct final form. It has been twenty years since the first genes controlling meristem development were molecularly cloned. In the intervening decades, our understanding of the inner workings directing meristem development has increased enormously. This review summarizes our current knowledge of how the meristem functions as a persistent organ generating center. The story that emerges is one in which transcription factor activity combines with the action of the classic plant growth regulators auxin and cytokinin and with the action of more recently discovered small peptides to control proliferation and cell fate in the shoot apical meristem.

    View details for DOI 10.1016/j.ydbio.2009.11.029

    View details for Web of Science ID 000276943100008

    View details for PubMedID 19961843

  • Partitioning the Apical Domain of the Arabidopsis Embryo Requires the BOBBER1 NudC Domain Protein PLANT CELL Jurkuta, R. J., Kaplinsky, N. J., Spindel, J. E., Barton, M. K. 2009; 21 (7): 1957-1971

    Abstract

    The apical domain of the embryo is partitioned into distinct regions that will give rise to the cotyledons and the shoot apical meristem. In this article, we describe a novel screen to identify Arabidopsis thaliana embryo arrest mutants that are defective in this partitioning, and we describe the phenotype of one such mutant, bobber1. bobber1 mutants arrest at the globular stage of development, they express the meristem-specific SHOOTMERISTEMLESS gene throughout the top half of the embryo, and they fail to express the AINTEGUMENTA transcript normally found in cotyledons. Thus, BOBBER1 is required to limit the extent of the meristem domain and/or to promote the development of the cotyledon domains. Based on expression of early markers for apical development, bobber1 mutants differentiate protodermis and undergo normal early apical development. Consistent with a role for auxin in cotyledon development, BOBBER1 mutants fail to express localized maxima of the DR5:green fluorescent protein reporter. BOBBER1 encodes a protein with homology to the Aspergillus nidulans protein NUDC that has similarity to protein chaperones, indicating a possible role for BOBBER1 in synthesis or transport of proteins involved in patterning the Arabidopsis embryo.

    View details for DOI 10.1105/tpc.108.065284

    View details for Web of Science ID 000270415700008

    View details for PubMedID 19648297

  • A feedback regulatory module formed by LITTLE ZIPPER and HD-ZIPIII genes PLANT CELL Wenkel, S., Emery, J., Hou, B., Evans, M. M., Barton, M. K. 2007; 19 (11): 3379-3390

    Abstract

    The Arabidopsis thaliana REVOLUTA (REV) protein is a member of the class III homeodomain-leucine zipper (HD-ZIPIII) proteins. REV is a potent regulator of leaf polarity and vascular development. Here, we report the identification of a gene family that encodes small leucine zipper-containing proteins (LITTLE ZIPPER [ZPR] proteins) where the leucine zipper is similar to that found in REV, PHABULOSA, and PHAVOLUTA proteins. The transcript levels of the ZPR genes increase in response to activation of a steroid-inducible REV protein. We show that the ZPR proteins interact with REV in vitro and that ZPR3 prevents DNA binding by REV in vitro. Overexpression of ZPR proteins in Arabidopsis results in phenotypes similar to those seen when HD-ZIPIII function is reduced. We propose a negative feedback model in which REV promotes transcription of the ZPR genes. The ZPR proteins in turn form heterodimers with the REV protein, preventing it from binding DNA. The HD-ZIPIII/ZPR regulatory module would serve not only to dampen the effect of fluctuations in HD-ZIPIII protein levels but more importantly would provide a potential point of regulation (control over the ratio of inactive heterodimers to active homodimers) that could be influenced by other components of the pathway governing leaf polarity.

    View details for DOI 10.1105/tpc.107.055772

    View details for Web of Science ID 000252268700007

    View details for PubMedID 18055602

  • The ins and outs of Arabidopsis embryogenesis DEVELOPMENTAL CELL Barton, M. K. 2007; 12 (6): 849-850

    Abstract

    In this issue of Developmental Cell, Nodine and colleagues show that two related leucine-rich repeat receptor kinases, RECEPTOR-LIKE PROTEIN KINASE1 and TOADSTOOL2, are critical in establishing radial pattern in the Arabidopsis embryo (Nodine et al., 2007). Embryos lacking these kinases show replacement of outer cell fates with inner cell fates.

    View details for DOI 10.1016/j.devcel.2007.05.010

    View details for Web of Science ID 000247119700006

    View details for PubMedID 17543858

  • Making holes in leaves: Promoting cell state transitions in stomatal development PLANT CELL Barton, M. K. 2007; 19 (4): 1140-1143

    View details for DOI 10.1105/tpc.107.051177

    View details for Web of Science ID 000246802200004

    View details for PubMedID 17468260

  • Interactions between the cell cycle and embryonic patterning in Arabidopsis uncovered by a mutation in DNA polymerase epsilon PLANT CELL Jenik, P. D., Jurkuta, R. E., Barton, M. K. 2005; 17 (12): 3362-3377

    Abstract

    Pattern formation and morphogenesis require coordination of cell division rates and orientations with developmental signals that specify cell fate. A viable mutation in the TILTED1 locus, which encodes the catalytic subunit of DNA polymerase epsilon of Arabidopsis thaliana, causes a lengthening of the cell cycle by approximately 35% throughout embryo development and alters cell type patterning of the hypophyseal lineage in the root, leading to a displacement of the root pole from its normal position on top of the suspensor. Treatment of preglobular and early globular stages, but not later stage, embryos with the DNA polymerase inhibitor aphidicolin leads to a similar phenotype. The results uncover an interaction between the cell cycle and the processes that determine cell fate during plant embryogenesis.

    View details for DOI 10.1105/tpc.105.036889

    View details for Web of Science ID 000233655700013

    View details for PubMedID 16278345

  • Surge and destroy: the role of auxin in plant embryogenesis DEVELOPMENT Jenik, P. D., Barton, M. K. 2005; 132 (16): 3577-3585

    Abstract

    For nearly a century, the plant hormone auxin has been recognized for its effects on post-embryonic plant growth. Now recent insights into the molecular mechanism of auxin transport and signaling are uncovering fundamental roles for auxin in the earliest stages of plant development, such as in the development of the apical-basal (shoot-root) axis in the embryo, as well as in the formation of the root and shoot apical meristems and the cotyledons. Localized surges in auxin within the embryo occur through a sophisticated transcellular transport pathway causing the proteolytic destruction of key transcriptional repressors. As we discuss here, the resulting downstream gene activation, together with other, less well-understood regulatory pathways, establish much of the basic body plan of the angiosperm embryo.

    View details for DOI 10.1242/dev.01952

    View details for Web of Science ID 000231998800001

    View details for PubMedID 16077088

  • MicroRNA binding sites in Arabidopsis class IIIHD-ZIP mRNAs are required for methylation of the template chromosome DEVELOPMENTAL CELL Bao, N., Lye, K. W., Barton, M. K. 2004; 7 (5): 653-662

    Abstract

    Dominant mutations in the Arabidopsis PHABULOSA (PHB) and PHAVOLUTA (PHV) transcription factor genes cause transformation of abaxial to adaxial leaf fates by altering a microRNA complementary site present in processed PHB and PHV mRNAs but not in the corresponding genomic DNA. phb-1d mutants accumulate excess PHB transcript throughout the leaf primordium, indicating defective regulation of PHB transcript synthesis and/or stability. We show that PHB and PHV coding sequences are heavily methylated downstream of the microRNA complementary site in most wild-type plant cells and that methylation is reduced in phb-1d and phv-1d mutants. Decreased methylation is limited to the chromosome bearing the dominant mutant allele in phb-1d heterozygotes. Low levels of methylation are detected in wt PHB DNA isolated from undifferentiated tissues. These results suggest a model in which the microRNA interacts with nascent, newly processed PHB mRNA to alter chromatin of the corresponding PHB template DNA predominantly in differentiated cells.

    View details for Web of Science ID 000225197100007

    View details for PubMedID 15525527

  • Plant biology - Plant acupuncture: Sticking PINs in the right places SCIENCE Kaplinsky, N. J., Barton, M. K. 2004; 306 (5697): 822-823

    View details for Web of Science ID 000224969400034

    View details for PubMedID 15514147

  • MicroRNA control of PHABULOSA in leaf development: importance of pairing to the microRNA 5 ' region EMBO JOURNAL Mallory, A. C., Reinhart, B. J., Jones-Rhoades, M. W., Tang, G. L., Zamore, P. D., Barton, M. K., Bartel, D. P. 2004; 23 (16): 3356-3364

    Abstract

    MicroRNAs (miRNAs) are approximately 22-nucleotide noncoding RNAs that can regulate gene expression by directing mRNA degradation or inhibiting productive translation. Dominant mutations in PHABULOSA (PHB) and PHAVOLUTA (PHV) map to a miR165/166 complementary site and impair miRNA-guided cleavage of these mRNAs in vitro. Here, we confirm that disrupted miRNA pairing, not changes in PHB protein sequence, causes the developmental defects in phb-d mutants. In planta, disrupting miRNA pairing near the center of the miRNA complementary site had far milder developmental consequences than more distal mismatches. These differences correlated with differences in miRNA-directed cleavage efficiency in vitro, where mismatch scanning revealed more tolerance for mismatches at the center and 3' end of the miRNA compared to mismatches to the miRNA 5' region. In this respect, miR165/166 resembles animal miRNAs in its pairing requirements. Pairing to the 5' portion of the small silencing RNA appears crucial regardless of the mode of post-transcriptional repression or whether it occurs in plants or animals, supporting a model in which this region of the silencing RNA nucleates pairing to its target.

    View details for DOI 10.1038/sj.emboj.7600340

    View details for Web of Science ID 000223732600017

    View details for PubMedID 15282547

  • Leaf development takes shape SCIENCE McConnell, J. R., Barton, M. K. 2003; 299 (5611): 1328-1329

    View details for Web of Science ID 000181192300032

    View details for PubMedID 12610287

  • Regulation of axis determinacy by the Arabidopsis PINHEAD gene PLANT CELL Newman, K. L., Fernandez, A. G., Barton, M. K. 2002; 14 (12): 3029-3042

    Abstract

    Plants produce proximal-distal growth axes with two types of growth potential: they can be indeterminate, in which case growth continues indefinitely, or they can be determinate, in which case growth is limited to the production of a single organ or a discrete set of organs. The indeterminate shoot axes of Arabidopsis pinhead/zwille mutants frequently are transformed to a determinate state. PINHEAD (PNH) is expressed in the central domain of the developing plant: the provascular tissue, the shoot apical meristem, and the adaxial (upper) sides of lateral organ primordia. Here, we show that ectopic expression of PNH on the abaxial (lower) sides of lateral organs results in upward curling of leaf blades. This phenotype correlates with a loss of cell number coordination between the two surfaces of the blade, indicating that ectopic PNH can cause changes in cell division rates. More strikingly, moving PNH expression from the central to the peripheral domain of the embryo causes transformation of the determinate cotyledon axis to an indeterminate state. We propose that growth axes are specified as determinate versus indeterminate in a PNH-mediated step. Our results add to a growing body of evidence that radial positional information is important in meristem formation. These results also indicate that genes regulating cell division and axis determinacy are likely to be among PNH targets.

    View details for DOI 10.1105/tpc.005132

    View details for Web of Science ID 000179936800006

    View details for PubMedID 12468725

  • Transformation of shoots into roots in Arabidopsis embryos mutant at the TOPLESS locus DEVELOPMENT Long, J. A., Woody, S., Poethig, S., Meyerowitz, E. M., Barton, K. 2002; 129 (12): 2797-2806

    Abstract

    We describe a novel phenotype in Arabidopsis embryos homozygous for the temperature-sensitive topless-1 mutation. This mutation causes the transformation of the shoot pole into a root. Developing topless embryos fail to express markers for the shoot apical meristem (SHOOT MERISTEMLESS and UNUSUAL FLORAL ORGANS) and the hypocotyl (KNAT1). By contrast, the pattern of expression of root markers is either duplicated (LENNY, J1092) or expanded (SCARECROW). Shifts of developing topless embryos between permissive and restrictive temperatures show that apical fates (cotyledons plus shoot apical meristem) can be transformed to basal fates (root) as late as transition stage. As the apical pole of transition stage embryos shows both morphological and molecular characteristics of shoot development, this demonstrates that the topless 1 mutation is capable of causing structures specified as shoot to be respecified as root. Finally, our experiments fail to show a clear link between auxin signal transduction and topless-1 mutant activity: the development of the apical root in topless mutant individuals is not dependent on the activity of the predicted auxin response factor MONOPTEROS nor is the expression of DR5, a proposed 'auxin maximum reporter', expanded in the apical domain of topless embryos.

    View details for Web of Science ID 000176769800002

    View details for PubMedID 12050130

  • Giving meaning to movement CELL Barton, M. K. 2001; 107 (2): 129-132

    Abstract

    A growing body of evidence indicates that plant transcription factors move between cells. A recent paper by Nakajima et al. (2001) shows that movement of the SHORTROOT protein provides a mechanism for signaling positional information between cell layers of the root.

    View details for Web of Science ID 000171694800002

    View details for PubMedID 11672520

  • Rescue of the shootmeristemless (stm) mutant phenotype by expression of STM mRNA in a subset of its normal domain: Implications for nonautonomous action of the STM transcription factor in Arabidopsis thaliana. DEVELOPMENTAL BIOLOGY Fernandez, A. G., Long, J. A., Joy, R. E., Barton, M. K. 2001; 235 (1): 260-260
  • Role of PHABULOSA and PHAVOLUTA in determining radial patterning in shoots NATURE McConnell, J. R., EMERY, J., Eshed, Y., Bao, N., Bowman, J., Barton, M. K. 2001; 411 (6838): 709-713

    Abstract

    The upper side of the angiosperm leaf is specialized for efficient capture of sunlight whereas the lower side is specialized for gas exchange. In Arabidopsis, the establishment of polarity in the leaf probably requires the generation and perception of positional information along the radial (adaxial versus abaxial or central versus peripheral) dimension of the plant. This is because the future upper (adaxial) side of the leaf develops from cells closer to the centre of the shoot, whereas the future under (abaxial) side develops from cells located more peripherally. Here we implicate the Arabidopsis PHABULOSA and PHAVOLUTA genes in the perception of radial positional information in the leaf primordium. Dominant phabulosa (phb) and phavoluta (phv) mutations cause a dramatic transformation of abaxial leaf fates into adaxial leaf fates. They do so by altering the predicted sterol/lipid-binding domains of ATHB14 and ATHB9, proteins of previously unknown function that also contain DNA-binding motifs. This change probably renders the protein constitutively active, implicating this domain as a central regulator of protein function and the PHB and PHV proteins as receptors for an adaxializing signal.

    View details for Web of Science ID 000169112500050

    View details for PubMedID 11395776

  • Leaving the meristem behind: regulation of KNOX genes GENOME BIOLOGY Barton, M. K. 2001; 2 (1)

    Abstract

    The mechanism by which the plant reserves some cells as pluripotent stem cells while partitioning others into differentiated leaf tissue is fundamental to plant development. New work in Arabidopsis elucidates the genetic circuitry that distinguishes meristem from leaf.

    View details for Web of Science ID 000207583500007

    View details for PubMedID 11178282

  • Initiation of axillary and floral meristems in Arabidopsis DEVELOPMENTAL BIOLOGY Long, J., Barton, M. K. 2000; 218 (2): 341-353

    Abstract

    Shoot development is reiterative: shoot apical meristems (SAMs) give rise to branches made of repeating leaf and stem units with new SAMs in turn formed in the axils of the leaves. Thus, new axes of growth are established on preexisting axes. Here we describe the formation of axillary meristems and floral meristems in Arabidopsis by monitoring the expression of the SHOOT MERISTEMLESS and AINTEGUMENTA genes. Expression of these genes is associated with SAMs and organ primordia, respectively. Four stages of axillary meristem development and previously undefined substages of floral meristem development are described. We find parallels between the development of axillary meristems and the development of floral meristems. Although Arabidopsis flowers develop in the apparent absence of a subtending leaf, the expression patterns of AINTEGUMENTA and SHOOT MERISTEMLESS RNAs during flower development suggest the presence of a highly reduced, "cryptic" leaf subtending the flower in Arabidopsis. We hypothesize that the STM-negative region that develops on the flanks of the inflorescence meristem is a bract primordium and that the floral meristem proper develops in the "axil" of this bract primordium. The bract primordium, although initially specified, becomes repressed in its growth.

    View details for Web of Science ID 000085517000019

    View details for PubMedID 10656774

  • Growth and development - Plants from genes: towards the information network - Editorial overview CURRENT OPINION IN PLANT BIOLOGY Barton, K., Scheres, B. 2000; 3 (1): 13-16
  • Shoot apical meristem formation and function in Arabidopsis. MOLECULAR BIOLOGY OF THE CELL Barton, M. K. 1999; 10: 2A-2A
  • The PINHEAD/ZWILLE gene acts pleiotropically in Arabidopsis development and has overlapping functions with the ARGONAUTE1 gene DEVELOPMENT Lynn, K., Fernandez, A., Aida, M., Sedbrook, J., Tasaka, M., Masson, P., Barton, M. K. 1999; 126 (3): 469-481

    Abstract

    Several lines of evidence indicate that the adaxial leaf domain possesses a unique competence to form shoot apical meristems. Factors required for this competence are expected to cause a defect in shoot apical meristem formation when inactivated and to be expressed or active preferentially in the adaxial leaf domain. PINHEAD, a member of a family of proteins that includes the translation factor eIF2C, is required for reliable formation of primary and axillary shoot apical meristems. In addition to high-level expression in the vasculature, we find that low-level PINHEAD expression defines a novel domain of positional identity in the plant. This domain consists of adaxial leaf primordia and the meristem. These findings suggest that the PINHEAD gene product may be a component of a hypothetical meristem forming competence factor. We also describe defects in floral organ number and shape, as well as aberrant embryo and ovule development associated with pinhead mutants, thus elaborating on the role of PINHEAD in Arabidopsis development. In addition, we find that embryos doubly mutant for PINHEAD and ARGONAUTE1, a related, ubiquitously expressed family member, fail to progress to bilateral symmetry and do not accumulate the SHOOT MERISTEMLESS protein. Therefore PINHEAD and ARGONAUTE1 together act to allow wild-type growth and gene expression patterns during embryogenesis.

    View details for Web of Science ID 000078713700005

    View details for PubMedID 9876176

  • The development of apical embryonic pattern in Arabidopsis DEVELOPMENT Long, J. A., Barton, M. K. 1998; 125 (16): 3027-3035

    Abstract

    The apical portion of the Arabidopsis globular stage embryo gives rise to the cotyledons and the shoot apical meristem (SAM). The SHOOT MERISTEMLESS (STM) gene is required for SAM formation during embryogenesis and for SAM function throughout the lifetime of the plant. To more precisely define the development of molecular pattern in the apical portion of the embryo, and the role of the STM gene in the development of this pattern, we have examined AINTEGUMENTA (ANT), UNUSUAL FLORAL ORGANS (UFO) and CLAVATA1 (CLV1) expression in wild-type and stm mutant embryos. The transcripts of these genes mark subdomains within the apical portion of the embryo. Our results indicate that: (1) the molecular organization characteristic of the vegetative SAM is not present in the globular embryo but instead develops gradually during embryogenesis; (2) radial pattern exists in the apical portion of the embryo prior to and independent of STM with STM expression itself responding to radial information; (3) the embryonic SAM consists of central and peripheral subdomains that express different combinations of molecular markers and differ in their ultimate fates; and (4) STM activity is required for UFO expression, STM is required for maintenance but not onset of CLV1 expression and the pattern of ANT expression is independent of STM.

    View details for Web of Science ID 000075749300003

    View details for PubMedID 9671577

  • Leaf polarity and meristem formation in Arabidopsis DEVELOPMENT McConnell, J. R., Barton, M. K. 1998; 125 (15): 2935-2942

    Abstract

    Shoot apical meristems (SAMs) of seed plants are small groups of pluripotent cells responsible for making leaves, stems and flowers. While the primary SAM forms during embryogenesis, new SAMs, called axillary SAMs, develop later on the body of the plant and give rise to branches. In Arabidopsis plants, axillary SAMs develop in close association with the adaxial leaf base at the junction of the leaf and stem (the leaf axil). We describe the phenotype caused by the Arabidopsis phabulosa-1d (phb-1d) mutation. phb-1d is a dominant mutation that causes altered leaf polarity such that adaxial characters develop in place of abaxial leaf characters. The adaxialized leaves fail to develop leaf blades. This supports a recently proposed model in which the juxtaposition of ad- and abaxial cell fates is required for blade outgrowth. In addition to the alteration in leaf polarity, phb-1d mutants develop ectopic SAMs on the undersides of their leaves. Also, the phb-1d mutation weakly suppresses the shoot meristemless (stm) mutant phenotype. These observations indicate an important role for adaxial cell fate in promoting the development of axiallary SAMs and suggest a cyclical model for shoot development: SAMs make leaves which in turn are responsible for generating new SAMs.

    View details for Web of Science ID 000075452200017

    View details for PubMedID 9655815

  • Cell type specification and self renewal in the vegetative shoot apical meristem CURRENT OPINION IN PLANT BIOLOGY Barton, M. K. 1998; 1 (1): 37-42

    Abstract

    The vegetative shoot apical meristem of seed plants is the site of new leaf and stem formation. In the past few years genes that regulate fundamental aspects of shoot growth and development have been discovered. The recent study of these genes and their products through the use of appropriate mutants has opened new doors to understanding the molecular mechanisms of shoot apical meristem function.

    View details for Web of Science ID 000075765400007

    View details for PubMedID 10066561

  • Genetics of angiosperm shoot apical meristem development ANNUAL REVIEW OF PLANT PHYSIOLOGY AND PLANT MOLECULAR BIOLOGY Evans, M. M., Barton, M. K. 1997; 48: 673-701
  • Hormonal studies of fass, an Arabidopsis mutant that is altered in organ elongation PLANT PHYSIOLOGY Fisher, R. H., Barton, M. K., Cohen, J. D., Cooke, T. J. 1996; 110 (4): 1109-1121
  • A member of the KNOTTED class of homeodomain proteins encoded by the STM gene of Arabidopsis NATURE Long, J. A., MOAN, E. I., Medford, J. I., Barton, M. K. 1996; 379 (6560): 66-69

    Abstract

    The KNOTTED class of plant genes encodes homeodomain proteins. These genes have been found in all plant species where they have been sought and, where examined, show expression patterns that suggest they play an important role in shoot meristem function. Until now, all mutant phenotypes associated with these genes have been due to gain-of-function mutations, making it difficult to deduce their wild-type function. Here we present evidence that the Arabidopsis SHOOT-MERISTEMLESS (STM) gene, required for shoot apical meristem formation during embryogenesis, encodes a class I KNOTTED-like protein. We also describe the expression pattern of this gene in the wild-type plant. To our knowledge, STM is the first gene shown to mark a specific pattern element in the developing plant embryo both phenotypically and molecularly.

    View details for Web of Science ID A1996TN21600055

    View details for PubMedID 8538741

  • GLD-1, A TUMOR-SUPPRESSOR GENE REQUIRED FOR OOCYTE DEVELOPMENT IN CAENORHABDITIS-ELEGANS GENETICS Francis, R., Barton, M. K., Kimble, J., Schedl, T. 1995; 139 (2): 579-606

    Abstract

    We have characterized 31 mutations in the gld-1 (defective in germline development) gene of Caenorhabditis elegans. In gld-1 (null) hermaphrodites, oogenesis is abolished and a germline tumor forms where oocyte development would normally occur. By contrast, gld-1 (null) males are unaffected. The hermaphrodite germline tumor appears to derive from germ cells that enter the meiotic pathway normally but then exit pachytene and return to the mitotic cycle. Certain gld-1 partial loss-of-function mutations also abolish oogenesis, but germ cells arrest in pachytene rather than returning to mitosis. Our results indicate that gld-1 is a tumor suppressor gene required for oocyte development. The tumorous phenotype suggests that gld-1(+) may function to negatively regulate proliferation during meiotic prophase and/or act to direct progression through meiotic prophase. We also show that gld-1(+) has an additional nonessential role in germline sex determination: promotion of hermaphrodite spermatogenesis. This function of gld-1 is inferred from a haplo-insufficient phenotype and from the properties of gain-of-function gld-1 mutations that cause alterations in the sexual identity of germ cells.

    View details for Web of Science ID A1995QE14500008

    View details for PubMedID 7713419

  • EFFECT OF MUTATIONS IN THE PINHEAD GENE OF ARABIDOPSIS ON THE FORMATION OF SHOOT APICAL MERISTEMS DEVELOPMENTAL GENETICS McConnell, J. R., Barton, M. K. 1995; 16 (4): 358-366
  • FORMATION OF THE SHOOT APICAL MERISTEM IN ARABIDOPSIS-THALIANA - AN ANALYSIS OF DEVELOPMENT IN THE WILD-TYPE AND IN THE SHOOT MERISTEMLESS MUTANT DEVELOPMENT Barton, M. K., Poethig, R. S. 1993; 119 (3): 823-831
  • FOG-1, A REGULATORY GENE REQUIRED FOR SPECIFICATION OF SPERMATOGENESIS IN THE GERM LINE OF CAENORHABDITIS-ELEGANS GENETICS Barton, M. K., Kimble, J. 1990; 125 (1): 29-39

    Abstract

    In wild-type Caenorhabditis elegans, the XO male germ line makes only sperm and the XX hermaphrodite germ line makes sperm and then oocytes. In contrast, the germ line of either a male or a hermaphrodite carrying a mutation of the fog-1 (feminization of the germ line) locus is sexually transformed: cells that would normally make sperm differentiate as oocytes. However, the somatic tissues of fog-1 mutants remain unaffected. All fog-1 alleles identified confer the same phenotype. The fog-1 mutations appear to reduce fog-1 function, indicating that the wild-type fog-1 product is required for specification of a germ cell as a spermatocyte. Two lines of evidence indicate that a germ cell is determined for sex at about the same time that it enters meiosis. These include the fog-1 temperature sensitive period, which coincides in each sex with first entry into meiosis, and the phenotype of a fog-1; glp-1 double mutant. Experiments with double mutants show that fog-1 is epistatic to mutations in all other sex-determining genes tested. These results lead to the conclusion that fog-1 acts at the same level as the fem genes at the end of the sex determination pathway to specify germ cells as sperm.

    View details for Web of Science ID A1990DA94700005

    View details for PubMedID 2341035

  • ANALYSIS OF THE ROLE OF TRA-1 IN GERMLINE SEX DETERMINATION IN THE NEMATODE CAENORHABDITIS-ELEGANS GENETICS Schedl, T., Graham, P. L., Barton, M. K., Kimble, J. 1989; 123 (4): 755-769

    Abstract

    In wild-type Caenorhabditis elegans there are two sexes, self-fertilizing hermaphrodites (XX) and males (XO). To investigate the role of tra-1 in controlling sex determination in germline tissue, we have examined germline phenotypes of nine tra-1 loss-of-function (lf) mutations. Previous work has shown that tra-1 is needed for female somatic development as the nongonadal soma of tra-1(lf) XX mutants is masculinized. In contrast, the germline of tra-1(lf) XX and XO animals is often feminized; a brief period of spermatogenesis is followed by oogenesis, rather than the continuous spermatogenesis observed in wild-type males. In addition, abnormal gonadal (germ line and somatic gonad) phenotypes are observed which may reflect defects in development or function of somatic gonad regulatory cells. Analysis of germline feminization and abnormal gonadal phenotypes of the various mutations alone or in trans to a deficiency reveals that they cannot be ordered in an allelic series and they do not converge to a single phenotypic endpoint. These observations lead to the suggestion that tra-1 may produce multiple products and/or is autoregulated. One interpretation of the germline feminization is that tra-1(+) is necessary for continued specification of spermatogenesis in males. We also report the isolation and characterization of tra-1 gain-of-function (gf) mutations with novel phenotypes. These include temperature sensitive, recessive germline feminization, and partial somatic loss-of-function phenotypes.

    View details for Web of Science ID A1989CC60200014

    View details for PubMedID 2612895

  • GAIN-OF-FUNCTION MUTATIONS OF FEM-3, A SEX-DETERMINATION GENE IN CAENORHABDITIS-ELEGANS GENETICS Barton, M. K., SCHEDL, T. B., Kimble, J. 1987; 115 (1): 107-119

    Abstract

    We have isolated nine gain-of-function (gf) alleles of the sex-determination gene fem-3 as suppressors of feminizing mutations in fem-1 and fem-2. The wild-type fem-3 gene is needed for spermatogenesis in XX self-fertilizing hermaphrodites and for male development in both soma and germ line of XO animals. Loss-of-function alleles of fem-3 transform XX and XO animals into females (spermless hermaphrodites). In contrast, fem-3(gf) alleles masculinize only one tissue, the hermaphrodite germ line. Thus, XX fem-3(gf) mutant animals have a normal hermaphrodite soma, but the germ line produces a vast excess of sperm and no oocytes. All nine fem-3(gf) alleles are temperature sensitive. The temperature-sensitive period is from late L4 to early adult, a period just preceding the first signs of oogenesis. The finding of gain-of-function alleles which confer a phenotype opposite to that of loss-of-function alleles supports the idea that fem-3 plays a critical role in germ-line sex determination. Furthermore, the germ-line specificity of the fem-3(gf) mutant phenotype and the late temperature-sensitive period suggest that, in the wild-type XX hermaphrodite, fem-3 is negatively regulated so that the hermaphrodite stops making sperm and starts making oocytes. Temperature shift experiments also show that, in the germ line, sexual commitment appears to be a continuing process. Spermatogenesis can resume even after oogenesis has begun, and oogenesis can be initiated much later than normal.

    View details for Web of Science ID A1987F688500013

    View details for PubMedID 3557107

Conference Proceedings


  • GENETIC-ANALYSIS OF MERISTEM STRUCTURE AND FUNCTION IN ARABIDOPSIS-THALIANA Barton, M. K. PLENUM PRESS DIV PLENUM PUBLISHING CORP. 1993: 69-73
  • GENETIC-CONTROL OF SEX DETERMINATION IN THE HERMAPHRODITE GERM LINE OF CAENORHABDITIS-ELEGANS Rosenquist, T., Ahringer, J., Barton, M. K., Graham, P., Okkema, P., Kimble, J. WILEY-LISS, INC. 1990: 91-102

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