Functional Analysis of B3 Domain Transcription Factors

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0322005McCartyIn all likelihood, plants and animals evolved multicellular structures independently. Plant genomes encode a remarkable number of DNA binding proteins that have no obvious homologs in other organisms. In many cases, these plant specific regulatory genes have been implicated in plant specific signaling pathways. The implication is that recruitment of novel transcription factors has played a major role in the independent evolution of plant development. One important family of plant specific transcription factors are identified as proteins containing the highly conserved B3 DNA binding domain. Four major sub-families of B3 domain proteins are identified in the Arabidopsis genome (VP1/ABI3, ARF, RAV and VPL groups). The ARF and VP1/ABI3 groups have been implicated in auxin and abscisic acid (ABA) hormone signaling pathways of plants, respectively. The functions of the RAV and VPL families are unknown. This project focuses on analyzing the functions of genes in the VP1/ABI3, RAV and VPL families. A common theme among the B3 proteins is a bivalent structure coupling B3 to autonomous protein interaction domains (VP1/ABI3 and ARF's) or to a second DNA binding domain (RAV). A key long term goal is to understand how interactions of DNA binding (B3) and protein-protein interaction (COAR) domains of the VP1 protein give rise to the extraordinary complexity of VP1/ABI3 regulated gene expression observed in the developing seed. The extensive genetics and resources available for Arabidopsis will be applied to analysis of VP1 mutants that discriminate B3 dependent and B3 independent regulatory functions. One approach will be to create mutant forms of VP1 that perturb B3 and its interaction with COAR and new mutations in other genes that specifically affect B3 regulated functions. The second objective will address the contribution of protein-protein interactions mediated by the COAR domain. Finally, the current model for VP1 function raises analogous questions concerning the role of B3 domains in other transcription factor families including the ARF, RAV and VPL families. The third objective focuses on developing tools for analysis of the RAV and VPL families of B3 transcription factors.