Mesophyll-specific overexpressing ofSvHXK6gene improves water use efficiency without yield loss in C4Setaria viridis

Abstract

AbstractHexokinases (HXK) were the first sugar signalling proteins identified in plants and are well known for their feedback regulation of photosynthetic gene expression. In some C3plants, HXKs have been found to regulate stomatal function. However, the role of HXK in C4photosynthesis, which is inherently more water use efficient than C3metabolism, remains poorly understood. Here, we report on the first tissue-specific modification of HXK in a C4plant.SvHXK6was expressed in the model C4grassSetaria viridisunder the control of theZmPEPCpromoter (ZmPEPCpro), which directs expression in the leaf mesophyll tissue. ThreeS. viridistransgenic lines with increased abundance ofSvHXK6transcripts in the leaf tissue showed significant reduction in stomatal conductance with minimal effects on leaf CO2assimilation rate. Consequently, the transgenic lines had higher leaf-level water use efficiency relative to the control (wild-type and null) plants. Overexpression ofSvHXK6had no effect on shoot biomass or seed yield of theS. viridisplants. Our study shows conserved function of HXK in regulating stomatal conductance in a C4grass, demonstrating possible widespread utility in improving water use efficiency in C4as well as C3species.