Self renewal is integral to the creation and maintenance of many tissues and organs including human epithelia, muscle and blood systems. Each of these tissues establishes populations of self-renewing (stem) cells and must ensure that these stem cells divide and create new differentiated cells at the appropriate rate and in the appropriate place;not enough cells or divisions and the tissue will deteriorate, too many divisions and tumors can form. Our long term goal is to understand the mechanism(s) by which dispersed self-renewing populations are established and how their division and differentiation is influenced by interaction with neighboring cells. A powerful set of genetic, molecular and functional genomic tools, combined with the ability to visualize and track cell divisions makes Arabidopsis stomatal development an attractive system for investigating this set of questions. In our previous work we found that a trio of bHLH transcription factors and components of a MAPK pathway modulate division vs. differentiation choices at discrete stages in stomatal development. Based on data from genetic, biochemical and functional assays, we propose that activity of the earliest-acting bHLH in this trio, SPEECHLESS (SPCH), controls the asymmetric divisions that create the self-renewing populations. We show that SPCH is a direct target of MAP kinase-dependent phosphorylation in vitro, and that phosphorylation alters the behavior of SPCH in vivo.
Our specific aims i n this proposal are to: (1) elucidate the molecular mechanisms by which SPCH activity is regulated (2) Create a molecular profile of stomatal lineage cells and identify and functionally characterize transcriptional targets of SPCH in these cells, and (3) Take advantage of SPCH-induced phenotypes to genetically dissect the endogenous signaling network required to repress stem-cell differentiation. Because both the bHLH class of transcriptional regulators and the MAPK pathway are universally conserved, these studies may contribute not only to an understanding of self-renewal, but will contribute to our understanding of the diversity of MAPK and bHLH signaling mechanisms and responses.
Adult stem cells are called upon to regenerate or repair tissues following injury or disease. However, excess division of those same stems can lead to cancer. The proposed studies will thus help to inform strategies to induce stem cells to differentiate into specific tissues while restricting the potential for cancerous overgrowth.
|Davies, Kelli A; Bergmann, Dominique C (2014) Functional specialization of stomatal bHLHs through modification of DNA-binding and phosphoregulation potential. Proc Natl Acad Sci U S A 111:15585-90|
|Lau, On Sun; Davies, Kelli A; Chang, Jessica et al. (2014) Direct roles of SPEECHLESS in the specification of stomatal self-renewing cells. Science 345:1605-9|
|Matos, Juliana L; Lau, On Sun; Hachez, Charles et al. (2014) Irreversible fate commitment in the Arabidopsis stomatal lineage requires a FAMA and RETINOBLASTOMA-RELATED module. Elife 3:|
|Bargmann, Bastiaan O R; Vanneste, Steffen; Krouk, Gabriel et al. (2013) A map of cell type-specific auxin responses. Mol Syst Biol 9:688|
|Kim, Tae-Wuk; Michniewicz, Marta; Bergmann, Dominique C et al. (2012) Brassinosteroid regulates stomatal development by GSK3-mediated inhibition of a MAPK pathway. Nature 482:419-22|
|Robinson, Sarah; Barbier de Reuille, Pierre; Chan, Jordi et al. (2011) Generation of spatial patterns through cell polarity switching. Science 333:1436-40|
|Hachez, Charles; Ohashi-Ito, Kyoko; Dong, Juan et al. (2011) Differentiation of Arabidopsis guard cells: analysis of the networks incorporating the basic helix-loop-helix transcription factor, FAMA. Plant Physiol 155:1458-72|
|MacAlister, Cora A; Bergmann, Dominique C (2011) Sequence and function of basic helix-loop-helix proteins required for stomatal development in Arabidopsis are deeply conserved in land plants. Evol Dev 13:182-92|
|Katsir, Leron; Davies, Kelli A; Bergmann, Dominique C et al. (2011) Peptide signaling in plant development. Curr Biol 21:R356-64|
|Rowe, Matthew H; Bergmann, Dominique C (2010) Complex signals for simple cells: the expanding ranks of signals and receptors guiding stomatal development. Curr Opin Plant Biol 13:548-55|