OsSIRH2-23, a rice salt-induced RING finger protein H2-23, contributes to insensitivity to salinity stress

Abstract

Degradation of proteins via the 26 S proteasome system is an important step in stress-responsive signaling networks in plants. Here, we characterized the rice RING-type E3 ligase gene, OsSIRH2–23, (previously named OsRFPH2–23) induced by salinity. OsSIRH2–23 encodes a cellular protein with a C3H2C3-RING finger domain in its C-terminal region and has E3 ligase activity. OsSIRH2–23 expression was substantially higher in the aboveground parts than in the subterranean part. The OsSIRH2–23-EYFP fusion protein was localized in the nucleus, cytoplasm, and plasma membrane under normal conditions, but mainly the cytoplasm and plasma membrane under saline conditions. Additionally, an interacting partner, OsSalT, jacalin-like lectin domain-containing protein, was identified using yeast two-hybrid and bimolecular fluorescence assays, and an in vitro ubiquitination assay showed that OsSIRH2–23 ubiquitinated the OsSalT protein. To investigate the possible role of OsSIRH2–23 in salt stress responses, the phenotypes of wild type (WT), OsSIRH2–23-overexpressing and ossirh2–23 T-DNA insertion mutant rice plants were analyzed. OsSIRH2–23-overexpressing plants showed better insensitivity to salinity than WT and ossirh2–23. OsSIRH2–23-overexpressing plants had a lower Na+/K+ ratio and higher accumulation of proline than WT and ossirh2–23 plants. Furthermore, qRT-PCR data suggested that OsSIRH2–23-overexpressing plants showed salt insensitivity by reinforcing the expression of several rice transporters (OsHKT1;5, OsHKT2;1, OsSOS1, and OsNHX1) involved in Na+/K+ homeostasis and salt-induced genes (OsDREB2A and OsNAC1) under salt stress conditions. Thus, these results provide experimental evidence that OsSIRH2–23 is an important regulator of Na+ and K+ regulation and plays a critical role in salt insensitivity, possibly by modulating the expression of transporters and salt-responsive genes.