Heterologous expression of rice annexin OsANN5 potentiates abiotic stress tolerance in transgenic tobacco through ROS amelioration

An earlier investigation showed that annexin OsANN5 of rice was expressed to high levels in various stress treatments. In the present study, we have investigated the molecular mechanism underlying stress responses of OsANN5 through heterologous expression in transgenic tobacco and E. coli. E. coli cells expressing OsANN5 showed improved growth under high salt and heat stress treatments. Transgenic tobacco plants overexpressing OsANN5 exhibited tolerance to salinity, drought and osmotic stress during seed germination and post-germinative stages. The transgenic plants showed increased accumulation of proline, reduced chlorosis and membrane damage as compared to the wild type plants. Higher expression of OsANN5 also resulted in efficient scavenging of reactive oxygen species through the modulation of anti-oxidant enzymes, superoxide dismutase and catalase under stress treatments. OsANN5 exhibited calcium binding activity and under salt stress, relocated from the peripheral regions to cytosol. This suggests that OsANN5 has multiple functions in rice growth and stress tolerance. Promoter analysis of OsANN5 revealed the presence of several cis-acting elements that are well known to be involved in hormonal and stress response regulation. The expression patterns of OsANN5 in the presence of ABA synthesis inhibitor, fluoridone and salinity stress revealed that upregulation of OsANN5 transcripts is regulated by both ABA-dependent and independent pathways. This indicates OsANN5 may play a role in cross-talk between ABA-dependent and independent pathways during the abiotic stress response.