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Background Inositol pyrophosphates (PP-InsPs) are high-energy derivatives of inositol, involved in different signalling and regulatory responses of eukaryotic cells. Distinct PP-InsPs species are characterized by the presence of phosphate at a variable number of the 6-carbon inositol ring backbone, and two distinct classes of inositol phosphate kinases responsible for their synthesis have been identified in Arabidopsis, namely ITPKinase (inositol 1,3,4 trisphosphate 5/6 kinase) and PP-IP5Kinase (diphosphoinositol pentakisphosphate kinases). Plant PP-IP5Ks are capable of synthesizing InsP8 and were previously shown to control defense against pathogens and phosphate response signals. However, other potential roles of plant PP-IP5Ks, especially towards abiotic stress, remain poorly understood. Results Here, we characterized the physiological functions of two Triticum aestivum L. (hexaploid wheat) PPIP5K homologs, TaVIH1 and TaVIH2. We demonstrate that wheat VIH proteins can utilize InsP7 as the substrate to produce InsP8, a process that requires the functional VIH-kinase domains. At the transcriptional level, both TaVIH1 and TaVIH2 are expressed in different wheat tissues, including developing grains, but show selective response to abiotic stresses during drought-mimic experiments. Ectopic overexpression of TaVIH2-3B in Arabidopsis confers tolerance to drought stress and rescues the sensitivity of Atvih2 mutants. RNAseq analysis of TaVIH2-3B-expressing transgenic lines of Arabidopsis shows genome-wide reprogramming with remarkable effects on genes involved in cell-wall biosynthesis, which is supported by the observation of enhanced accumulation of polysaccharides (arabinogalactan, cellulose, and arabinoxylan) in the transgenic plants. Conclusions Overall, this work identifies a novel function of VIH proteins, implicating them in modulation of the expression of cell-wall homeostasis genes, and tolerance to water-deficit stress. This work suggests that plant VIH enzymes may be linked to drought tolerance and opens up the possibility of future research into using plant VIH-derived products to generate drought-resistant plants.

Peaches are good source of nutrients and known for their taste and aroma. The highly perishable nature of the peaches tends to decay rapidly during transportation and storage is a serious constraint for efficient transportation and storage. Therefore, the effect of arabinoxylan (AX) and β-D-glucan stearic acid ester (SABG) composite coating material was examined for the postharvest storage quality of peach under storage at 22 ± 2 °C with 85% relative humidity (RH). Both, AX-SABG and shellac (1–2%) coatings significantly reduced the change in the quality attributes like weight loss (1.2–1.4 fold), respiration rate (1.1–1.2 fold), ripening index (1.3–1.5 fold) and firmness (1.3–1.5 fold) during 6 days storage as compared to the uncoated peaches. In addition, AX-SABG (1–2%) coating was more effective in retaining aroma volatiles and reducing disease incidence compared to shellac. Further, acute and chronic toxicological studies have shown no tissue related toxicity and mortality in mice. Our results suggest that AX-SABG as an edible coating has the potential to preserve the fruit quality during 6 days storage at 22 ± 2 °C and extend the postharvest shelf life of peach during storage.

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.

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