Heterogeneous Expression of Plasma-membrane-localised OsOSCA1.4 Complements Osmotic Sensing Based on Hyperosmolality and Salt Stress in Arabidopsis Osca1 Mutant

In plants, both hyperosmolality and salt stress induce cytosolic calcium increases within seconds, referred to as the hyperosmolality-induced [Ca] increases, OICI, and salt stress-induced [Ca] increases, SICI. Previous studies have shown that Arabidopsis reduced hyperosmolality-induced [Ca] increase 1 (OSCA1.1) encodes a hyperosmolality-gated calcium-permeable channel that mediates OICI in guard cells and root cells. Multiple OSCA members exist in plants; for example, Oryza sativa has 11 OsOSCAs genes, indicating that OSCAs have diverse biological functions. Here, except for OsOSCA4.1, ten full-length OsOSCAs were separately subcloned, in which OsOSCA1.4 was exclusively localised to the plasma membrane and other nine OsOSCAs-eYFP co-localised with an endoplasmic reticulum marker in Arabidopsis mesophyll protoplasts. OsOSCA1.4 was further identified as a calcium-permeable ion channel that activates an inward current after receiving an osmotic signal exerted by hyperosmolality or salt stress, and mediates OICI and SICI in human embryonic kidney 293 (HEK293) cells. Moreover, overexpression of OsOSCA1.4 in Arabidopsis osca1 mutant complemented osmotic Ca signalling, root growth, and stomatal movement in response to hyperosmolality and salt stress. These results will facilitate further study of OsOSCA-mediated calcium signalling and its distinct roles in rice growth and development.