Regulatory Systems controlling Plant Cell Axis formation, Stem Cell Specification and Plant Pathogen Defense

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Plant architecture is anchored in a polar shoot-root axis. This axis becomes extensively branched above and below ground through the reiterative generation of new organs. Despite their amazing morphological diversity, higher vascular plants share this basic architecture and the molecular mechanisms underlying the formation of a polar axis in the early plant embryo as well as many of the mechanism operating in the terminal stem cell populations, called apical meristems, as they generate new organs and allocate new stem cell niches (meristems) for continued growth. Plants are also well known for their impressive ability to generate new shoot-root axes from disorganized tissue or even single cells in a process called regeneration, which is of utmost importance for plant breeding and biotechnology. This proposal is built on early findings, which linked auxin perception and auxin transport to the embryonic formation of a body axis, the positioning of lateral organs and leave vascular patterns and the de novo generation of new stem cell niches for shoot formation in plant tissue culture. Starting from Arabidopsis embryo mutants, auxin transport interference and visualization experiments, and based on this, the isolation of the first functional Auxin Response Factor (ARF), we made contributions to the understanding of auxin driven patterning processes in various organs. More recently, we have complemented those contributions by supplying cohorts of ARF target genes, among them genes within the auxin singling network as well as genes in the specification of auxin flow paths. Strikingly, these analytical entries have led to the discovery of a versatile genetic tool, with which we can improve the de novo establishment of stem cell niches, most dramatically in the formation of shoots during plant tissue regeneration, using a modified ARF gene, MP?, as a genetic switch. At this point, three obvious target areas need to urgently be addressed. (1) The shoot promoting activity of MP? needs to better understood, optimized and applied to more plant species. (2) The molecular reasons why one ARF protein, MP, has properties, not found in other ARFs, needs to be determined, (3) the signaling pathway through which MP controls patterning processes during regeneration and other processes needs to be further elucidated. This will involve the conversion of already identified target genes, regulated by MP, into visualization tools as well as the use and development of other novel visualization markers in hormone signal transduction. Those will not only be limited to patterning processes, but in the context of other collaborative efforts, will also include hormone markers in pathogen responses.