Functional validation of a small GTP binding Protien PgRab7 in rice for abiotic stress tolerance

Abstract

Small GTP-binding proteins are ubiquitous among eukaryotes. In plants Rab proteins form the largest family of the small GTPases. They are involved in a wide variety of cellular processes in eukaryotic cells including, signal transduction, cell proliferation, vesicular transport and cytoskeletal organization. Very little information exists on the role of intracellular vesicle trafficking in tolerance with reference to environmental stresses particularly abiotic stress in plants. The present study was therefore undertaken to functionally characterize the role of PgRab7 a small GTP-binding protein from Pennisetum glaucum, a relatively drought-stress tolerant food grain crop, in different abiotic stresses with particular reference to salinity and drought stress. The amino acid sequence of OsRab7 and PgRab7 proteins showed 92.3 % identity and the protein structures are also highly similar. Rice has four orthologs of Rab7 distributed on only 2 chromosomes. The transgenic rice plant overexpressing PgRab7 were developed and confirmed by PCR and Western blot analysis. Measurement of different photosynthetic parameters of WT and transgenic plants under control conditions suggest that transgenic plants have better photosynthesis efficiency than WT. Leaf disc senescence assay and T2 seed germination assay under NaCl stress showed that transgenic plants have better tolerance towards salinity stress than WT. Transgenic lines growing throughout in 200 mM salinity stress and two months old transgenic plants provided with 200 mM NaCl stress upto seed harvest showed that transgenic plants have better tolerance capacity at vegetative stage as compared to WT but showed yield penalty as tested by seed weights. The better tolerance at vegetative stage may be due to high chlorophyll level and better photosynthetic efficiency. The mechanism of tolerance of transgenic lines to salinity stress may be due to increase in vacuolar volume, intact chloroplast, less oxidative stress, less Na+ penetration to root cell and high K+/ Na+ ratio.