Cold stress is one of the major factors that limiting rice production and geographical distribution. Elucidating the molecular mechanisms of cold signal transduction is the base of molecular design breeding. Our study found that Oryza sativa Calreticulin 3 (OsCRT3) exhibits conformational changes under cold stress, thereby enhancing its interaction with CBL-interacting protein kinase 7 (OsCIPK7) to sense cold. OsCRT3 localizes at the ER and mediates increases in cytosolic calcium levels under cold stress. Cold stress triggers secondary structural changes of OsCRT3 and enhances its binding affinity with OsCIPK7, which finally boosts its kinase activity (EMBO J, 2023).
We also identified a receptor like kinase CTPK1 (Cold tolerance protein kinase1) that could interact with OsCRT3. CTPK1 negatively regulates rice chilling tolerance at seedling stage. CTPK1 is activated by cold stress via extracellular hydrogen peroxide. Besides, CTPK1 interacts and phosphorylates receptor like cytoplasmic kinase OsRLCK to transduce the cold signal from the membrane to the cytoplasm. OsRLCK is localized at plasma membrane via palmitoylation.The key phosphorylation site of OsRLCK phosphorylated by CTPK1 was identified. Genome evolution analysis suggests that CTPK1 might originate from Chinese O. Rufipogon and a natural variation affects the kinase activity of CTPK1.
Taken together, our results identify a cold-sensing mechanism that simultaneously conveys cold-induced protein conformational change, enhances kinase activity, and Ca2+ signal generation to facilitate chilling tolerance in rice. Besides, we also reveal that cold induced extracellular hydrogen peroxide as a signal to balance plant growth and stress response, offering valuable insights for breeding of cold-tolerant rice varieties.