Genome-wide expressional and functional analysis of calcium transport elements during abiotic stress and development in rice

Ca2+ homeostasis is required to maintain a delicate balance of cytosolic Ca2+ during normal and adverse growth conditions. Various Ca2+ transporters actively participate to maintain this delicate balance especially during abiotic stresses and developmental events in plants. In this study, we present a genome- wide account, detailing expression profiles, subcellular localization and functional analysis of rice Ca2+ transport elements. Exhaustive in silico data mining and analysis resulted in the identification of 81 Ca2+ transport element genes, which belong to various groups such as Ca2+-ATPases (pumps), exchangers, channels, glutamate receptor homologs and annexins. Phylogenetic analysis revealed that different Ca2+ transporters are evolutionarily conserved across different plant species. Comprehensive expression analysis by gene chip microarray and quantitative RT-PCR revealed that a substantial proportion of Ca2+ transporter genes were expressed differentially under abiotic stresses (salt, cold and drought) and reproductive developmental stages (panicle and seed) in rice. These findings suggest a possible role of rice Ca2+ transporters in abiotic stress and development triggered signaling pathways. Subcellular localization of Ca2+ transporters from different groups in Nicotiana benthamiana revealed their variable localization to different compartments, which could be their possible sites of action. Complementation of Ca2+ transport activity of K616 yeast mutant by Ca2+-ATPase OsACA7 and involvement in salt tolerance verified its functional behavior. This study will encourage detailed characterization of potential candidate Ca2+ transporters for their functional role in planta.