CNGC-interacting calmodulin OsCaM1.1 regulates cytosolic Ca2+ signals and promotes tolerance to abiotic stresses in rice

Cytosolic calcium ion (Ca2+) signals are important for abiotic stress tolerance in plants; however, their generation and regulation remain poorly understood. Here, we show that the rice calmodulin (CaM) protein OsCaM1.1 regulates multiple aspects of Ca2+ signals and modulates abiotic stress tolerance and growth in rice. OsCaM1.1 increases stress tolerance to heat, chilling, salt, and drought, as demonstrated by both its loss-of-function mutants and its overexpression lines. It promotes Ca2+ influx and stomatal closure in response to heat, chilling, salt, and the hormone abscisic acid. OsCaM1.1 can physically interact with multiple Ca2+ channel cyclic nucleotide-gated channel (CNGC) proteins, and overexpression of OsCNGC16 rescued defects of both stress tolerance and stomatal closure in the OsCaM1.1 mutant, indicating that OsCaM1.1 regulates CNGC proteins for its stress tolerance function. Under non-stress conditions, OsCaM1.1 promotes Ca2+ oscillations in root hairs and enhances root hair elongation. It also maintains low basal cytosolic Ca2+ levels under non-stress conditions. These findings indicate that OsCaM1.1 is a regulator of both transient Ca2+ signals and resting or basal Ca2+ signals. OsCaM1.1 likely functions in stress tolerance and regulates transient Ca2+ signals through Ca2+ channel CNGC proteins.