Energy-sensing kinase OsSnRK1b and its regulator OsCTK1 promote chilling-induced stomatal closure and cold tolerance.

Low temperatures can present a major challenge to plant growth and development. Here we report that low energy response and stomatal closure are two important responses for plant cold tolerance. The rice SNF1-Related Kinase 1b (OsSnRK1b) has an evolutionarily conserved function in low energy response. Its protein abundance is positively regulated by a cold tolerance regulator Chilling Tolerance Kinase 1 (OsCTK1) through phosphorylation. Both OsCTK1 and OsSnRK1b promote chilling-induced stomatal closure and chilling tolerance, while overexpression of OsSnRK1b enhances stomatal closure and chilling tolerance in an OsCTK1-dependent manner. In addition, chilling induces low energy response which is largely dependent on OsSnRK1b. Both OsCTK1 and OsSnRK1b are required for the induction of stress response gene Abscisic Acid Insensitive 5 (OsABI5) and the inhibition of growth-associated processes under chilling. CTK1 homologs in Arabidopsis and maize also positively regulate cold tolerance and cold induced stomatal closure, indicating a conserved role of low energy response and stomatal aperture control in plant cold tolerance.