Cold‐induced calreticulin OsCRT3 conformational changes promote OsCIPK7 binding and temperature sensing in rice

Unusually low temperatures caused by global climate change adversely affect rice production. Sensing cold to trigger signal network is a key base for improvement of chilling tolerance trait. Here, we report that Oryza sativa Calreticulin 3 (OsCRT3) localized at the endoplasmic reticulum (ER) exhibits conformational changes under cold stress, thereby enhancing its interaction with CBL‐interacting protein kinase 7 (OsCIPK7) to sense cold. Phenotypic analyses of OsCRT3 knock‐out mutants and transgenic overexpression lines demonstrate that OsCRT3 is a positive regulator in chilling tolerance. OsCRT3 localizes at the ER and mediates increases in cytosolic calcium levels under cold stress. Notably, cold stress triggers secondary structural changes of OsCRT3 and enhances its binding affinity with OsCIPK7, which finally boosts its kinase activity. Moreover, Calcineurin B‐like protein 7 (OsCBL7) and OsCBL8 interact with OsCIPK7 specifically on the plasma membrane. Taken together, our results thus identify a cold‐sensing mechanism that simultaneously conveys cold‐induced protein conformational change, enhances kinase activity, and Ca 2+ signal generation to facilitate chilling tolerance in rice. Synopsis Cold sensors convert physical signals into protective responses. Here, an OsCRT3‐OsCIPK7 protein‐protein interaction senses cold through conformational changes which enhance their binding affinity. The plant‐specific calreticulin OsCRT3 is a positive regulator of chilling tolerance in rice. OsCRT3, as an ER‐localized protein, regulates changes in cytosolic calcium concentration to protect against cold stress. Conformational changes to OsCRT3 triggered by cold stress enhance its ability to bind to and stimulate kinase activity of OsCIPK7. A cold‐elicited Ca 2+ signal is sensed by the calcium sensor OsCBL7/8, which specifically interacts with OsCIPK7 on the plasma membrane. Graphical Abstract A plant‐specific calreticulin regulates cytosolic calcium levels and OsCIPK7 kinase activity to protect against cold stress.