Associate Professor (Compressed) Washington State University Pullman, Washington
Body of Abstract: Background. Switchgrass is a promising species for production of lignocellulosic biofuels and conversion efficiency depends on the composition and structure of the cell walls, especially lignin content. MYB4 is a negative regulator of lignin biosynthesis, whose over expression results in plants with significant improvements in enzymatic digestibility of cellulose for conversion to biofuels. At the same time, these changes may have unintended consequences for plant performance, particularly hydraulic function, as there is generally a positive correlation between tissue lignin content and drought resistance. In this study, we characterized cell wall and physiological responses of a Ubipro-PvMY4 overexpression transgenic switchgrass line and its untransformed wild type (WT) for physiological and cell wall responses to water restriction applied during the internode elongation stage of development in large mesocosms in the greenhouse.
Results. Under well-watered conditions relative to WT, over MYB4 over expression caused a decrease in switchgrass stem lignin (14%) and a decrease in para-coumaric acid (pCA) on lignin (20%) and on xylan (29%), consistent with previous results (Baxter et al., 2015, BioEnergy Res8:910). The engineered line showed no effects on amounts of cellulose or ferulic acid (FA) on lignin, but a 16% decrease in on FA on xylan. Dry biomass was decreased by 70% in transgenic, but photosynthesis has increased by 11%, which is probably due to the reduction of lignin. Water restriction significantly decreased WT shoot dry weight, root+shoot dry weight, photosynthesis, and water potential; while the transgenic appeared to be unaffected. Also, drought caused a significant cell wall changes in WT, including a decrease in lignin and cellulose and an increase in pCA on lignin and in total pCA, while cell wall changes in the MYB4 line were not significant.
Conclusions. Although the transgenic has produces less biomass and dry weight the genotype is more resistance to drought