Regulatory Systems Controlling Plant Cell Axis Formation and Regenerative Stem Cell Formation

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The molecular mechanisms by which cells in multicellular organisms acquire distinct cell fates to form functionally meaningful body patterns, termed biological pattern formation, are still largely unknown. A better molecular understanding of pattern formation is important for avoidance of unscheduled cancerous cell proliferation in most multicellular organisms and specifically in plants also for optimized growth, resource allocation, certain types of stress resistance and hence improved yield. Yield improvements, in turn, are associated with benefits for the world’s ecology, economy and human development. A critical component in understanding pattern formation is the identification of the precise molecular determinants that define various stem cell niches. Specifically in plants, our insufficient molecular insights into stem cell niche formation has severely handicapped breeding and biotechnology, as it has kept many agronomically highly important plant species recalcitrant to in-vitro regeneration, a prerequisite for vegetative propagation, mass assessment of traits, rescue of endangered species and transformation. In recent years, significant progress to better understand pattern formation has been made in a number of model organisms, predominantly based on genetic approaches followed by large-scale genomic and targeted molecular strategies. In plants, these approaches have converged in the fascinating cell-biological interconnection of multicellular patterning with polarity acquisition of the individual plant cell. As it turned out, a huge number of seemingly separate patterning processes, including embryo axis formation, internal organization in both apical meristems, the formation of lateral organs in shoots and roots and even phyllotaxis and vascular patterning could be attributed to the polar transport and feed-back controlled distribution of a single simple molecule, indole-acetic acid (IAA, an auxin "phytohormone”) through individual cells. Auxin is perceived and translated into gene-regulatory responses, including those controlling its transport by Auxin Response (transcription) Factors (ARFs) and their nuclear co-regulators of the Aux/IAA family (1). Based on extensive work with the auxin transcriptional regulation genes, this proposal outlines strategies to (a) use specific genetic switches to dramatically increase plant regeneration properties as well as stem cell activities in lateral meristems, (b) analyze other pathways controlling stem cell properties in plants based on the results of small compound screens, (c) continue to unravel the functional genomics of the ARF-Aux/IAA regulatory network through a novel type of ARF variants and (d) identify novel regulators controlling vascular cell properties based on identified Quantitative Trait Loci.