Overexpression of the phosphatidylinositol synthase gene from Zea mays in tobacco plants alters the membrane lipids composition and improves drought stress tolerance

Phosphatidylinositol (PtdIns) is an important lipid because it serves as a key membrane constituent and is the precursor of the inositol-containing lipids that are found in all plants and animals. It is synthesized from cytidine-diphosphodiacylglycerol (CDP-DG) and myo-inositol by PtdIns synthase (PIS). We have previously reported that two putative PIS genes from maize (Zea mays L.), ZmPIS and ZmPIS2, are transcriptionally up-regulated in response to drought (Sui et al., Gene, 426: 47-56, 2008). In this work, we report on the characterization of ZmPIS in vitro and in vivo. The ZmPIS gene successfully complemented the yeast pis mutant BY4743, and the determination of PIS activity in the yeast strain further confirmed the enzymatic function of ZmPIS. An ESI-MS/MS-based lipid profiling approach was used to identify and quantify the lipid species in transgenic and wildtype tobacco plants before and after drought treatment. The results show that the overexpression of ZmPIS significantly increases lipid levels in tobacco leaves under drought stress compared to those of wild-type tobacco, which correlated well with the increased drought tolerance of the transgenic plants. Further analysis showed that, under drought stress conditions, ZmPIS overexpressors were found to exhibit increased membrane integrity, thereby enabling the retention of more solutes and water compared with the wild-type and the vector control transgenic lines. Our findings give us new insights into the role of the ZmPIS gene in the response of maize to drought/osmotic stress and the mechanisms by which plants adapt to drought stress.