A role for transcriptional repression in plant embryonic axis formation

植物和动物的胚胎都沿着极轴发育。在植物中，这形成了顶端的茎池和基根的极点。这一轴的正确形成对所有植物的胚后生长至关重要。转录辅阻遏子TPL(TPL)被证明可以阻止基根基因在胚胎顶端茎杆中的表达。在TPL-1突变体中，茎杆转化为第二根杆，从而产生两端都有根杆的幼苗。TPL的作用是与转录抑制因子BODLENOS(BDL)(AUX/IAA蛋白)和转录激活因子Monopteros(MP)(生长素反应因子(ARF))形成复合体。这种复合体的形成受植物激素生长素的调节--当生长素水平较高时，BDL被降解，MP随后可以激活正常的根和维管系统发育所需的基因。该项目试图确定受TPL/BDL/MP复合体调控的靶基因，并通过基因筛选确定该途径的新组成部分。还将对BDL在胚胎细胞水平上抑制转录的能力进行详细分析。最后，还将探讨胚胎发育过程中其他AUX/IAA蛋白对TPL活性的依赖关系。由于这一途径在所有高等植物中都是保守的，阐明和理解它的作用机制将直接适用于农业上重要的作物，并将为我们提供必要的工具来改变植物的形态和生长模式。这项工作将在博士后、本科生和高中阶段提供科学培训，并将包括代表性不足的少数民族。这项提案还将产生用于K-12学生和教师教育外展的材料。

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.