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Drought and high salinity are environmental conditions that cause adverse effects on the growth and productivity of crops. Aquaporins are small integral membrane proteins that belong to the family of the major intrinsic proteins (MIPs), with members in animals, plants and microbes, where they facilitate the transport of water and/or small neutral solutes thereby affecting water balance. In this study we characterized two aquaporin genes namely, plasma membrane intrinsic protein (PIP2;7) and tonoplast intrinsic protein TIP1;3 from Jatropha curcas that are localised to the plasma membrane and vacuole respectively. Transgenic Arabidopsis thaliana lines over-expressing JcPIP2;7 and JcTIP1;3 under a constitutive promoter show improved germination under high salt and mannitol compared to control seeds. These transgenic plants also show increased root length under abiotic stress conditions compared to wild type Col-0 plants. Transgenic lines exposed to drought conditions by withholding water for 20 days, were able to withstand water stress and attained normal growth after re-watering unlike control plants which could not survive. Transgenic lines also had better seed yield than control under salt stress. Importantly, seed viability of transgenic plants grown under high salt concentration was 35%-45% compared to less than 5% for control seeds obtained from plants growing under salt stress. The effect of JcPIP2;7 and JcTIP1;3 on improving germination and seed viability in drought and salinity make these important candidates for genetic manipulation of plants for growth in saline soils.

Activating transcription factor 1 (ATF1) and the closely related proteins CREB (cyclic AMP resonse element binding protein) and CREM (cyclic AMP response element modulator) constitute a subfamily of bZIP transcription factors that play critical roles in the regulation of cellular growth, metabolism, and survival. Previous studies demonstrated that CREB is phosphorylated on a cluster of conserved Ser residues, including Ser-111 and Ser-121, in response to DNA damage through the coordinated actions of the ataxia-telangiectasia-mutated (ATM) protein kinase and casein kinases 1 and 2 (CK1/2). Here, we show that DNA damage-induced phosphorylation by ATM is a general feature of CREB and ATF1. ATF1 harbors a conserved ATM/CK cluster that is constitutively and stoichiometrically phosphorylated by CK1 and CK2 in asynchronously growing cells. Exposure to DNA damage further induced ATF1 phosphorylation on Ser-51 by ATM in a manner that required prior phosphorylation of the upstream CK residues. Hyperphosphorylated ATF1 showed a 4-fold reduced affinity for CREB-binding protein. We further show that PP2A, in conjunction with its targeting subunit B56gamma, antagonized ATM and CK1/2-dependent phosphorylation of CREB and ATF1 in cellulo. Finally, we show that CK sites in CREB are phosphorylated during cellular growth and that phosphorylation of these residues reduces the threshold of DNA damage required for ATM-dependent phosphorylation of the inhibitory Ser-121 residue. These studies define overlapping and distinct modes of CREB and ATF1 regulation by phosphorylation that may ensure concerted changes in gene expression mediated by these factors.