Overexpression of an aquaporin gene PvPIP2;9 improved biomass yield, protein content, drought tolerance and water use efficiency in switchgrass (Panicum virgatum L.)

Abstract

Switchgrass (Panicum virgatum L.) is a prime candidate for non-grain-based bioenergy feedstock production. Improved drought tolerance and higher water use efficiency (WUE) are important for its successful field establishment and production, especially on marginal lands. Aquaporins are key channels and regulators for water transportation and maintenance of cellular water status. In this study, the functional role of an aquaporin gene, PvPIP2;9, in switchgrass was studied. Expression of PvPIP2;9 was regulated by diurnal oscillation and osmotic stress. Constitutive over-expressing PvPIP2;9 in switchgrass significantly improved its leaf length, plant height, aboveground biomass and biomass protein contents under both drought- and non-stressed conditions, and also resulted in higher cellulose content in drought-stressed transgenic than wild-type plants. Under 21 days of drought treatment, transgenic plants showed less electrolyte leakage rates, but higher relative water contents, photochemical efficiencies, chlorophyll contents and WUE, indicating that PvPIP2;9 positively regulated plant drought tolerance. Moreover, expression patterns of all 14 switchgrass PIP2 subfamily genes were checked during the drought treatment, and the result showed that over-expressing PvPIP2;9 also affected transcript levels of most other PIP2 genes. Together, this study showed that improved biomass yield, drought tolerance and higher WUE can be achieved by manipulating the expression of PvPIP2;9 and also suggested PIP2 subfamily genes were transcriptionally regulated in a coordinated manner, which can be used for potential targets for crop drought resistance breeding efforts.