Post-doctoral research associate Oak Ridge National Laboratory Oak Ridge, Tennessee
Body of Abstract: In plants, a diverse array of secondary metabolites derives from the phenylpropanoids pathway. This includes molecules such as lignin, flavonoids and coumarins, that play essential roles in plant structure and defense, and are determinants for agronomic traits such as biomass recalcitrance and nutritional quality. Genome-wide association studies performed on a population of more than a thousand Populus trichocarpa natural variants uncovered an association between a gene encoding an isoform of 5-enolpyruvylshikimate 3-phosphate synthase (PtrEPSP-TF) and lignin content in woody tissues. Functional characterization of the gene revealed a dual role for that isoform. In addition to its canonical function in the shikimate pathway PtrEPSP-TF acquired a new function as transcriptional regulator of cell wall and lignin biosynthesis genes. Detailed analysis of the gene structure revealed that this isoform acquired an additional DNA-binding helix-turn-helix (HTH) motif in the N terminus, which is essential for conferring a transcription factor activity. In poplar, PtrEPSP-TF was shown to activate lignin biosynthesis through transcriptional regulation of a master regulator of cell wall formation. When introduced in rice, in which no dual function isoform of EPSP synthase was detected, PtrEPSP-TF induced lignification through regulation of five transcription factors. In this study, we investigate the function of some of these transcription factors in the regulation of lignin biosynthesis in another monocot species, switchgrass. Transgenic plants overexpressing one of the MYB transcription factors showed reduced stem lignin content, accompanied with an accumulation of secondary metabolites. This suggests that some of the regulators identified could play key roles in carbon partitioning, regulating carbon fluxes toward monolignols or flavonoids biosynthesis, two competing branches of the phenylpropanoids pathway. Besides expanding the fundamental knowledge on the molecular mechanisms underlying carbon sequestration into cell wall polymers such as lignin, this explores new strategies for engineering biomass properties for bioenergy applications.