The C2 domain-containing and Ca²⁺-binding protein OsERG1 interferes with OsPYL10-OsPP2C09 module to negatively...

In plants, C2 domain-containing proteins (C2DPs) constitute a large Ca²⁺-binding family involved in development and abiotic stress response. However, how it regulates the abscisic acid (ABA) signaling under chilling in rice is largely unknown. Here, we identified OsERG1, encoding a small C2 domain protein with binding Ca²⁺ in vitro, was induced obviously by cold stress and negatively regulated chilling tolerance in rice seedlings. An ABA receptor OsPYL10 was screened out from a yeast two-hybrid (Y2H) cDNA library using OsERG1 as bait. Furthermore, OsERG1 specifically interacted with OsPYL10 in both Ca²⁺- and ABA-dependent manners in vitro and in vivo. Moreover, both OsERG1 and OsPP2C09 interacted with the CL2 loop of OsPYL10 in the Y2H assay; OsERG1 was able to compete with OsPP2C09 for the interaction with OsPYL10 in the competitive in vitro pull-down assay. In addition, overexpression of OsERG1 and ospyl10 mutation showed a similar hyposensitive response of shoot growth to ABA application during the germination stage, suggesting the interrupting role of OsERG1 in the OsPYL10-OsPP2C09 module in rice. RNA-seq analysis confirmed that OsERG1 and OsPYL10 differentially regulated the expression of candidate genes in the ABA biosynthesis and ABA signaling, including OsNAC5, OsbZIP62, and OsbZIP46 under chilling. These findings provide the regulatory role of OsERG1 to the OsPYL10-OsPP2C09 module, and reveal new insight into the mechanism of chilling stress signaling and response in rice seedlings.