Cyclic nucleotide-gated ion channel 6 mediates thermotolerance in Arabidopsis seedlings by regulating nitric oxide production via cytosolic calcium ions.

BACKGROUND

We previously reported the involvement of nitric oxide (NO) and cyclic nucleotide-gated ion channel 6 (CNGC6) in the responses of plants to heat shock (HS) exposure. To elucidate their relationship with heat tolerance in Arabidopsis thaliana, we examined the effects of HS on several groups of seedlings: wild type, cngc6, and cngc6 complementation and overexpression lines.

RESULTS

After HS exposure, the level of NO was lower in cngc6 seedlings than in wild-type seedlings but significantly elevated in the transgenic lines depending on CNGC6 expression level. The treatment of seeds with calcium ions (Ca) enhanced the NO level in Arabidopsis seedlings under HS conditions, whereas treatment with EGTA (a Ca chelator) reduced it, implicating that CNGC6 stimulates the accumulation of NO depending on an increase in cytosolic Ca ([Ca]). This idea was proved by phenotypic observations and thermotolerance testing of transgenic plants overexpressing NIA2 and NOA1, respectively, in a cngc6 background. Western blotting indicated that CNGC6 stimulated the accumulation of HS proteins via NO.

CONCLUSION

These data indicate that CNGC6 acts upstream of NO in the HS pathway, which improves our insufficient knowledge of the initiation of plant responses to high temerature.