Título:MYB46-Mediated Transcriptional Regulatory Program is a Gatekeeper of Secondary Wall Biosynthesis
Palestrante:Kyung-Hwan Han -  Michigan State University
Data:09.05.16
Hora:11h
Local:SALA 132 - DEPTO. BOTÂNICA - IB/USP

Short abstract:
The secondary cell wall is a defining feature of xylem cells and allows them to resist both gravitational forces and the forces of the tension associated with the transpirational pull on their internal columns of water. Also, secondary walls constitute the majority of plant biomass, which is of primary importance to humans as fiber, pulp for paper manufacture, and as an environmentally cost-effective renewable source of energy. Formation of secondary wall requires coordinated transcriptional regulation of the genes involved in the biosynthesis of major secondary wall components (e.g., cellulose, hemicellulose, and lignin). Complex transcriptional networks appear to be involved in the coordinated regulation of secondary wall biosynthesis, including several MYB transcription factors. Transcription factor MYB46 and its paralog, MYB83, have been shown to function as a master switch for the secondary wall biosynthetic program in Arabidopsis thaliana. Overexpression of MYB46/MYB83 results in ectopic deposition of secondary walls in the cells that are normally parenchymatous, while suppression of its function reduces secondary wall thickening. Recently, we have discovered that MYB46 directly regulates the expression of all of the three cellulose synthases (CESA4, CESA7 and CESA8) that are necessary for secondary wall in Arabidopsis plants. We then demonstrated that MYB46 is not only direct regulator but also an obligate component of the transcriptional regulatory complex for functional expression of the three secondary wall-associated CESAs. Furthermore, we obtained experimental evidence that MYB46 also directly regulates key genes in hemicellulose and lignin biosynthesis. Based these observations, we hypothesize that MYB46 activates its target genes in multiple layers of the transcriptional network, which results in coordinated regulation of the biosynthesis of secondary walls. We are testing this hypothesis by identifying and functionally characterizing the components of the MYB46-mediated transcriptional regulatory network. Understanding of the regulatory program may lead to better strategies to biotechnologically control and uncouple the biosynthetic pathways for the three major components and, hence, pathway-specific engineering of biomass quality and quantity.