Arabidopsis CaM3 inhibits nitric oxide accumulation and improves thermotolerance by promoting S-nitrosoglutathione reductase via direct binding

Calmodulin 3 (CaM3) is a key component of heat shock (HS) signal transduction in Arabidopsis (Arabidopsis thaliana). We previously reported that nitric oxide (NO) acts as an upstream signal of AtCaM3 in plant thermotolerance. In this study, we demonstrated the effect of AtCaM3 on NO accumulation in the tolerance of Arabidopsis plants to HS. In vivo and in vitro protein–protein interaction assays displayed a direct binding between AtCaM3 and S-nitrosoglutathione reductase (GSNOR), inducing an increased GSNOR activity and an inhibited NO level. The cam3 mutant seedlings exhibited a high internal NO accumulation under HS. A gsnor deficiency decreased the survival ratio of cam3 plants accompanied by an increased internal NO level. However, treatment with 2-phenyl-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide (cPTIO, a special NO scavenger) elevated the survival ratio of cam3 mutant seedlings under HS conditions. Collectively, these data suggest an interesting finding that AtCaM3 serves as a signal in plant thermotolerance by reducing excessive NO accumulation through the binding and promoting of GSNOR, suggesting a feedback inhibition between AtCaM3 and NO in thermotolerance.