Guard-cell Targeted Overexpression of Arabidopsis Hexokinase 1 May Improve Water Use Efficiency in Field-Grown Tobacco Plants

Abstract

Water deficit currently acts as one of the largest limiting factors for agricultural productivity worldwide. Additionally, limitation by water scarcity is projected to continue in the future with the further onset of effects of global climate change. As a result, it is critical to develop or breed for crops that have increased water-use efficiency and that are more capable of coping with water-scarce conditions. However, increased intrinsic water-use efficiency (iWUE) typically comes with a trade-off to CO2 assimilation as all gas exchange is mediated by stomata, through which CO2 enters the leaf while water vapor exits. Previously, promising results were shown about using guard-cell targeted overexpression of hexokinase to increase iWUE without incurring a penalty to photosynthetic rates or biomass production. Here, two homozygous transgenic lines expressing AtHXK1 constitutively (35SHXK2 and 35SHXK5) and a line that had guard-cell targeted overexpression of AtHXK1 (GCHXK2) were evaluated relative to wild type (WT) for traits related to photosynthesis and yield. In this study significantly better iWUE was found in GCHXK2 relative to WT without negatively impacting CO2 assimilation, although results were dependent upon leaf age and proximity of precipitation event to gas exchange measurement.