Wheat inositol pyrophosphate kinase TaVIH2-3B modulates cell-wall composition for drought tolerance in Arabidopsis

Abstract

Inositol pyrophosphates (PPx□InsPs) are of key interest, since they are known to participate in multiple physiological processes from lower eukaryotes to humans. However, limited knowledge is available for their role in plants and especially in crops. In this study, two diphosphoinositol pentakisphosphate kinase PPIP5K wheat homologs, TaVIH1 and TaVIH2 were identified and characterized for their spatio-temporal expression along with their physiological functions. The biochemical assay demonstrated the presence of active VIH-kinase domains as evident from the InsP6 phosphorylation activity. The yeast complementation assays showed differential function, where only TaVIH2-3B was capable of rescuing the growth defects of yeast vip1Δ genotype. Reporter assays with TaVIH2-promoter in Arabidopsis displayed strong GUS expression in response to dehydration stress and Pi-starvation with similar observations noted at the transcriptional level. In an attempt to identify VIH2 function, a yeast two hybrid screen of wheat library resulted in the identification of multiple interacting proteins primarily associated with cell-wall. One such interactor of wheat VIH2-3B was identified to be a Fasciclin-like arabinogalactan protein (FLA6) that was confirmed by pull-down assay. Systematic analysis of transgenic Arabidopsis overexpressing TaVIH2-3B protein showed robust growth and enhanced relative water content when compared to controls. Biochemical analysis of their cell-wall components in the shoots resulted in increased accumulation of polysaccharides such as cellulose, arabinogalactan and arabinoxylan, whereas Atvih2-3 mutant showed decrease in some of these components. Overall, our results provide novel insight into the functional role of inositol pyrophosphate kinases that modulate cell-wall components so as to provide tolerance towards the dehydration stress.