Progress in the participation of Ca2+–calmodulin in heat shock signal transduction

A novel heat shock (HS) signal transduction pathway in plants for the participation of Ca2+–calmodulin (CaM) in HS signal transduction was identified. HS induces a rapid increase in intracellular free calcium ion levels ([Ca2+]i), and the involvement of phospholipase C-inositol 1,4,5-trisphosphate is one of the factors leading to elevation in [Ca2+]i induced by HS. HS also increases the expression of the CaM gene and the accumulation of the CaM protein. The CaM isoform, AtCaM3, in Arabidopsis is a key member in the HS signal transduction pathway. AtCaM3 regulates the activity of CaM-binding protein kinase (AtCBK3) or protein phosphatase (AtPP7), promoting the activation of the HS transcription factor, AtHSFA1a, by phosphorylation/dephosphorylation and the expression of heat shock protein genes, then improving heat tolerance in plants.