The Physiological Basis of Drought Stress Responsiveness of Switchgrass Genotypes with Altered Cell Wall Metabolism

PANAHABADI R; MONTEOLIVA MI; HUGHES J; NONAVINAKERE CHANDRAKANTH N; MCCARTHY HR; BARTLEY LE

Savanna, Georgia

Congreso; Plant biology 2023; 2023

ASPB

Background. Switchgrass is a promising species for production of lignocellulosic biofuels, but the conversion efficiency depends on the composition and structure of the cell walls, especially lignin content. MYB4 is a negative regulator of lignin biosynthesis, whose overexpression 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-PvMYB4 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, Ox-MYB4 overexpression caused a decrease in switchgrass stem lignin (14%) and a decrease in para-coumaric acid (pCA) in lignin (23%) and in xylan (28%), consistent with previous results (Baxter et al., 2015, BioEnergy Res 8:910). The engineered line showed no effects on amounts of cellulose or ferulic acid (FA) in lignin, but a 12% decrease in on FA on xylan. Although photosynthesis increased by 11% in transgenic plants, dry biomass was decreased by 70%, 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 significant lignin changes in plants, including a decrease in lignin in WT and increase in the Ox-MYB4 line; however, most other  cell wall components were not significant under drought conditions.​Conclusions. Although the transgenic produced less biomass, the genotype is more resistance to drought.