CML20,an Arabidopsis Calmodulin-like Protein,Negatively Regulates Guard Cell ABA Signaling And Drought Stress Tolerance

Drought is one of the main abiotic stresses in restraining of plant growth and development,so as to affect the crop yields.To screen the plant drought responsive genes and elucidate their functional molecular mechanism will be essentially needed for development of water-efficient,high-yield and stress-tolerant modernized agriculture.Guard cells shrink in response to abscisic acid(ABA)and drought,which is caused by efflux of ions that in turn reduces stomatal aperture and improves the plant's ability to retain moisture.Cytosolic free calcium is an essential secondary messenger in guard cell ABA signaling,but the details of this regulatory pathway remain sketchy.Here,the calmodulin-like protein CML20,which has four EF-hand domains and calcium-binding activity in vitro,was found to be a negative regulator of ABA-induced stomatal movement in Arahidopsis.The guard cells of cml20 loss-of-function mutant plants were hypersensitive to both ABA-activated S-type anion currents,and ABA inhibited inward K~+ currents than those of wild type.Additional,due to smaller stomatal aperture,cml20 showed less water loss from the leaves than wild type.These phenotypes of CML20 overexpressing plants contrasted with wild type in the opposite direction.The cml20 guard cells' response to drought and ABA suggested that CML20 contributes in ABA signaling by regulating the reactive oxygen species.In cml20,the genes MYB2,RAB18,ERD10,COR47 and RD29A responded positively at the transcriptional level to drought stress or ABA treatment.The findings of this report implicate that,in Arabidopsis thaliana,CML20 acts as a negative regulator of both ABA-induced stomatal movement and drought stress-response.