Transcript expression profiling of annexin genes in Oryza sativa group Indica cv. IR64 under osmotic stress
Environmental stresses severely affect crop survival, growth and grain yield, creating an urgent need to develop stress-tolerant varieties to sustain agricultural productivity. Abiotic stress signals often induce rapid fluctuations in cytosolic calcium levels, which are decoded by calcium-binding proteins to activate downstream signaling pathways. Annexins constitute a diverse multigene family of calcium-responsive proteins that play important roles across the eukaryotic kingdom. In plants, several annexin homologues have been identified. High concentrations of sodium chloride (NaCl), D-mannitol and polyethylene glycol (PEG) are commonly used to impose osmotic stress and simulate drought- or salinity-like conditions. To elucidate the role of rice annexins under osmotic stress, their expression profiles were analyzed in Oryza sativa group Indica cv. IR64 using endpoint RT-PCR. Ten-day-old seedlings were exposed to varying concentrations of NaCl, D-mannitol and PEG. RNA was isolated at two time points during a time-course experiment. Semi-quantitative RT-PCR was employed to examine the expression of seven annexin genes. The results revealed distinct and differential expression patterns among the annexin genes across treatments, indicating gene-specific responses to different osmotic stress conditions during early seedling development. Collectively, these findings suggest that annexins may play important regulatory roles in mediating osmotic stress responses in rice.