OsACA6, a P-type 2B Ca2+ ATPase functions in cadmium stress tolerance in tobacco by reducing the oxidative stress load

Main conclusion The present study demonstrates the first direct evidence of the novel role of OsACA6 in providing Cd (2+) stress tolerance in transgenic tobacco by maintaining cellular ion homeostasis and modulating ROS-scavenging pathway. Cadmium, a non-essential toxic heavy metal, interferes with the plant growth and development. It reaches the leaves through xylem and may become part of the food chain, thus causing detrimental effects to human health. Therefore, there is an urgent need to develop strategies for engineering plants for Cd2+ tolerance and less accumulation. The members of P-type ATPases family transport metal ions including Cd2+, and thus play important role an ion homeostasis. The present study elucidates the role of P-type 2B Ca2+ ATPase (OsACA6) in Cd2+ stress tolerance. The transcript levels of OsACA6 were up-regulated upon Cd2+, Zn2+ and Mn2+ exposure. Transgenic tobacco expressing OsACA6 showed tolerance towards Cd2+ stress as demonstrated by several physiological indices including root length, biomass, chlorophyll, malondialdehyde and hydrogen peroxide content. The roots of the transgenic lines accumulated more Cd2+ as compared to shoot. Further, confocal laser scanning microscopy showed that Cd2+ exposure altered Ca2+ uptake in OsACA6 transgenic plants. OsACA6 expression in tobacco also protected the transgenic plants from oxidative stress by enhancing the activity of enzymatic (SOD, CAT, APX, GR) and non-enzymatic (GSH and AsA) antioxidant machinery. Transgenic lines also tolerated Zn2+ and Mn2+ stress; however, tolerance for these ions was not as significant as observed for Cd2+ exposure. Thus, overexpression of OsACA6 confers Cd2+ stress tolerance in transgenic lines by maintaining cellular ion homeostasis and modulating reactive oxygen species (ROS)-scavenging pathway. The results of the present study will help to develop strategies for engineering Cd2+ stress tolerance in economically important crop plants.