| Plant MYB transcription factors show structural similarity to the oncogenic MYB protein first described in the avian myeloblastoma virus. MYB transcription factors play an important role in multiple aspects of plant development, including the production of anthocyanin, seed coat mucilage, root hairs, and trichomes. In Arabidopsis thaliana over one hundred genes encoding MYB-like family members have been identified.In this thesis, the discovery of several new MYB family members is described. These genes lie in tandem on Chromosome 2, and are members of the CAPRICE-LIRE MYB subfamily of transcriptional regulators. Similar to other CAPRICE-LIRE MYBS, the new MYB genes described herein contain a single myb DNA binding domain and lack an acidic activation domain. RT-PCR experiments confirm that all three genes are transcribed. Quite unexpectedly, chimeric RT-PCR products were found which suggest that two of the three CAPRICE-LIRE Chromosome 2 (CPLCH2) MYBS are capable of undergoing intergenic splicing.Sequence data suggested that the new CAPRICE-LIKE MYBs, along with the closely related TRY gene, act as transcriptional repressors rather than as transcriptional activators. To test the biological function of the CPLCH2 genes in vivo, multiple experiments were performed. Temporal-spatial expression patterns of the three CPLCH2 MYB genes were studied through RT-PCR, as well as through examination of plants transformed with a GUS reporter gene driven by putative promoter sequence from each MYB. Other experiments included phenotypic examination of T-DNA insertional mutants, as well as in planta overexpression studies. It was found that plants homozygous for a T-DNA insertion in intron 2 of MYB2 develop ectopic trichomes on the petioles of first leaves, and transgenic plants overexpressing any of the CPLCH2 MYB genes as GFP fusions are glabrous. Yeast two-hybrid assays confirm that all three CPLCH2 MYB proteins are capable of binding to GL3 protein. Taken together, these results suggest that the three new CAPRICE-LIKE Chromosome 2 family members play an important role in trichome development. It is hypothesized that the proteins encoded by these three genes act to prevent specific cells from developing into trichomes. |
