A role for transcriptional repression in plant embryonic axis formation

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Both plant and animal embryos develop along a polar axis. In plants, this gives rise to the apical shoot pool and the basal root pole. The proper formation of this axis is critical for the postembryonic growth of all plants. The transcriptional co-repressor TOPLESS (TPL) has been shown to prevent the expression of basal root genes in the apical shoot pole of the embryo. In tpl-1 mutants, the shoot pole is transformed into a second root pole, giving rise to seedlings with root poles on both ends. TPL acts by forming a complex with the transcriptional repressor BODLENOS (BDL)(an AUX/IAA protein) and the transcriptional activator MONOPTEROS (MP)(an Auxin Response Factor (ARF)). The formation of this complex is regulated by the plant hormone auxin-when auxin levels are high, BDL is degraded and MP can then activate genes required for proper root and vasculature development. This project seeks to identify the target genes that are regulated by the TPL/BDL/MP complex and identify new components of the pathway through genetic screens. A detailed analysis of the BDL's ability to repress transcription on a cellular level in the embryo will also be performed. Finally, the dependence of other AUX/IAA proteins on TPL activity will be explored during embryogenesis. As this pathway is conserved among all higher plants, the elucidation and understanding of the mechanisms by which it acts will be directly applicable to agriculturally important crops, and will provide us with the tools necessary to modify plants's form and growth patterns. This work will provide scientific training at the postdoctoral, undergraduate and high school levels and will include underrepresented minorities. This proposal will also generate materials used for K-12 student and teacher educational outreach.