Abiotic stress results in massive loss of crop productivity throughout the world. Because of our limited knowledge of the plant defense mechanisms, it is very difficult to exploit the plant genetic resources for manipulation of traits that could benefit multiple stress tolerance in plants. To achieve this, we need a deeper understanding of the plant gene regulatory mechanisms involved in stress responses. Understanding the roles of different members of plant gene families involved in different stress responses, would be a step in this direction. Arabidopsis, which served as a model system for the plant research, is also the most suitable system for the functional characterization of plant gene families. Annexin family in Arabidopsis also is one gene family which has not been fully explored. Eight annexin genes have been reported in the genome of Arabidopsis thaliana. Expression studies of different Arabidopsis annexins revealed their differential regulation under various abiotic stress conditions. AnnAt8 (At5g12380), a member of this family has been shown to exhibit ~433 and ~175 fold increase in transcript levels under NaCl and dehydration stress respectively. To characterize Annexin8 (AnnAt8) further, we have generated transgenic Arabidopsis and tobacco plants constitutively expressing AnnAt8, which were evaluated under different abiotic stress conditions. AnnAt8 overexpressing transgenic plants exhibited higher seed germination rates, better plant growth, and higher chlorophyll retention when compared to wild type plants under abiotic stress treatments. Under stress conditions transgenic plants showed comparatively higher levels of proline and lower levels of malondialdehyde compared to the wild-type plants. Real-Time PCR analyses revealed that the expression of several stress-regulated genes was altered in AnnAt8 over-expressing transgenic tobacco plants, and the enhanced tolerance exhibited by the transgenic plants can be correlated with altered expressions of these stress-regulated genes. Our findings suggest a role for AnnAt8 in enhancing abiotic stress tolerance at different stages of plant growth and development.

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GhNAC4 transcription factor from cotton localizes to vascular bundles and is highly upregulated by phytohormones and environmental stresses.

The current study on putative rice annexin OsAnn5 was tried to know its functional role in the abiotic stress tolerance. For this an in silico analysis of its protein sequence and upstream region was carried out. This results in identification of several probable potential sites for posttranslational modifications and cis-elements respectively. We have studied the effect of OsAnn5 in the amelioration of abiotic stress tolerance through heterologous expression in transgenic tobacco and E.coli. It is observed that OsAnn5 over expression leads to enhanced tolerance to abiotic stress through efficient scavenging of the ROS and balanced expression of SOD and CAT antioxidant enzymes in both the systems, under stress treatments. Fluorescent signal for transiently expressed EGFP:OsANN5 fusion protein was localized in the peripheral region of the onion epidermal cells under salt stress treatment. Expression analysis of OsAnn5 under ABA synthesis inhibitor, fluridone and salinity stress revealed that OsAnn5 appears to act through an ABA-independent pathway under salt stress and in support to this 35S:OsAnn5 transgenics seedlings exhibited less sensitivity to externally applied ABA.