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.

Aldehyde dehydrogenase (ALDH) carries out oxidation of toxic aldehydes using NAD⁺/NADP⁺ as cofactors. In the present study, we performed a genome-wide identification and expression analysis of genes in the ALDH gene family in Brassica rapa. A total of 23 ALDH genes in the superfamily have been identified according to the classification of ALDH Gene Nomenclature Committee (AGNC). They were distributed unevenly across all 10 chromosomes. All the 23 Brassica rapa ALDH (BrALDH) genes exhibited varied expression patterns during treatments with abiotic stress inducers and hormonal treatments. The relative expression profiles of ALDH genes in B. rapa showed that they are predominantly expressed in leaves and stem suggesting their function in the vegetative tissues. BrALDH7B2 showed a strong response to abiotic stress and hormonal treatments as compared to other ALDH genes; therefore, it was overexpressed in heterologous hosts, E. coli and yeast to study its possible function under abiotic stress conditions. Over-expression of BrALDH7B2 in heterologous systems, E. coli and yeast cells conferred significant tolerance to abiotic stress treatments. Results from this work demonstrate that BrALDH genes are a promising and untapped genetic resource for crop improvement and could be deployed further in the development of drought and salinity tolerance in B. rapa and other economically important crops.

CBL interacting protein kinases play important roles in adaptation to stress conditions. In the present study, we isolated a CBL-interacting protein kinase homolog(AdCIPK5)from a wild peanut (Arachis diogoi) with similarity toAtCIPK5of Arabidopsis. Expression analyses in leaves of the wild peanut showedAdCIPK5induction by exogenous signaling molecules including salicylic acid, abscisic acid and ethylene or abiotic stress factors like salt, PEG and sorbitol. The recombinant AdCIPK5-GFP protein was found to be localized to the nucleus, plasma membrane and cytoplasm. We overexpressedAdCIPK5in tobacco plants and checked their level of tolerance to biotic and abiotic stresses. While wild type and transgenic plants displayed no significant differences to the treatment with the phytopathogen,Phytophthora parasiticapvnicotianae, the expression ofAdCIPK5increased salt and osmotic tolerance in transgenic plants. Analysis of different physiological parameters revealed that the transgenic plants maintained higher chlorophyll content and catalase activity with lower levels of H₂O₂and MDA content during the abiotic stress conditions.AdCIPK5overexpression also contributed to the maintenance of a higher the K⁺/Na⁺ratio under salt stress. The enhanced tolerance of transgenic plants was associated with elevated expression of stress-related marker genes;NtERD10C,NtERD10D,NtNCED1,NtSus1,NtCATandNtSOS1. Taken together, these results indicate that AdCIPK5 is a positive regulator of salt and osmotic stress tolerance.