Energy sensing OsSnRK1b and its regulator OsCTK1 promote chilling-induced stomatal closure and chilling tolerance in rice

Plants employ diverse physiological strategies for cold tolerance. Here we report an important role of low energy response and stomatal closure control in chilling tolerance through the study of SNF1-Related Kinase 1 (OsSnRK1) and its regulator Chilling Tolerance Kinase 1 (OsCTK1) in rice. OsSnRK1b, an isoform of OsSnRK1 alpha subunit, is found to have an evolutionarily conserved function in low energy response. It is positively regulated by OsCTK1 at the protein stability level through phosphorylation. Both OsCTK1 and OsSnRK1b promote chilling-induced stomatal closure and chilling tolerance, shown by slower stomatal closure and lower survival rate after chilling exposure in their respective loss of function mutants. Transcriptome analysis revealed that chilling induces low energy response which is largely dependent on OsSnRK1b. Overexpression of OsSnRK1b enhanced chilling induced stomatal closure response and promoted chilling tolerance in an OsCTK1-dependent manner. Furthermore, both OsCTK1 and OsSnRK1b promote expression of stress response gene Abscisic Acid Insensitive 5 (OsABI5) and inhibit accumulation of growth-associated ribosome protein OsRPS6 under chilling conditions. The function of CTK1 and SnRK1 in chilling tolerance, stomatal control, and growth inhibition are also observed in Arabidopsis and maize, indicating a conserved role of energy signaling in chilling tolerance and a contribution of stomatal aperture control to chilling tolerance in plants.