Identifying the role of Casparian strip membrane proteins in rice under salinity stress

Casparian strip (CS) is a specialized structure in endodermal cell layer of plant roots and is critical for regulating hydro-mineral transport and thus plant growth and stress responses. CS are synthesized and stabilized by a specialized class of proteins called CS-membrane-domain-proteins, the CS membrane proteins (CASPs) (CASPs). CASPs have been identified in various crops; however, such studies on Indica rice cultivars remain limited. This study was conducted to identify and characterize putative CASPs in Indica rice varieties, and their influence on expression patterns of key genes under salinity stress. The genome-wide screening revealed five putative orthologs in the Indica genome, three of them were confirmed as stable and functional CASPs through Eggnogg, Protparam, gene structure and domain architecture analysis. Cis-regulatory element analysis showed abscisic acid-responsive element (ABRE) and anaerobic responsive element (ARE) promoter within the promoter region, indicating their roles in regulating plant hormones, stress-responses, and influencing developmental processes. Subcellular localization confirmed their presence on plasma membrane. Three-dimensional structures prediction showed that all CASPs have four transmembrane architectures. To analyze responses under salinity stress, two Indica rice varieties differing in salinity tolerance abilities were studied for their responses to salinity stress including reactive oxygen species generation, lipid peroxidation, and responsive antioxidant enzyme activities. Varietal and stress-responsive differential enzyme activity was seen particularly for peroxidases, which are known to be involved in CS formation. Histochemical visualization for the development of CS using propidium iodide diffusion confirmed the varietal difference under salinity stress. Differential qRT-PCR-based gene expression of identified genes further confirmed the role of CS under salinity stress.