Involvement of Ca2+ and CaM3 in Regulation of Thermotolerance in Lily (Lilium longiflorum)

Involvement of calcium (Ca2+) and different calmodulin (CaM) isoforms in heat shock (HS) signal transduction in lily (Lilium longiflorum) was investigated in this study. Application of CaCl2 enhanced the thermotolerance of lily, whereas treatment with calcium ion chelator EGTA and CaM antagonist trifluoperazine (TFP) lowered the thermotolerance. Besides, HS-induced expression of LlHsf1 and LlHsfA2 genes were up-regulated by CaCl2 and down-regulated by EGTA or TFP. These findings implied that Ca2+-CaM were involved in HS signal transduction in lily via HSF pathway. Subsequently, five LlCaM genes encoding three canonical CaM isoforms were isolated and characterized, among which the LlCaM3 expression was induced by heat and CaCl2 and correlated positively with thermotolerance of lily. Additionally, transient expression analysis determined LlCaM3 to be a cytoplasm and nucleus protein. Furthermore, overexpression of LlCaM3 in Arabidopsis (Arabidopsis thaliana) increased the transcript level of AtHsfA1a and AtHsp18.2 following HS and improved the thermotolerance of transgenic plants. Taken together, the results suggest that LlCaM3 is a key component in Ca2+-CaM HS signaling pathway in lily and may be in the upstream of HSF.