The knockout of tobacco NtCBL10 inhibits leaf Cl- accumulation and leads to light-dependent necrosis & light-independent chlorosis under salt stress

CBL10 was shown to be a key gene for salt tolerance in Arabidopsis thaliana. In this study, we evaluated the role of CBL10 in the tobacco salt tolerance response by characterizing the gene editing-induced loss-of-function knockout mutants of the two NtCBL10 homeologous genes NtCBL10A and NtCBL10B. The importance of NtCBL10 for the response to salinity was evidenced by the salt supersensitivity of the Nt-cbl10a10b double mutants, with fast-developing chlorosis and severe necrotic lesions on leaves. Stomatal conductance and photochemical efficiency of photosystem 2 (PhiPS2) of the Nt-cbl10a10b double mutant were significantly inhibited already at a very early stage of the salt stress response. Leaf Na+ concentrations were not much affected in these plants, but the Cl- content of the Nt-cbl10a10b double mutants was significantly lower than that of wild-type plants, which is the first report of CBL10 in the regulation of Cl- homeostasis. Interestingly, the necrosis phenotype of Ntcbl10a10b double mutants was dependent on light, while the chlorosis phenotype of Nt-cbl10a10b double mutants was light-independent. Different from the previous studies that focus on the role of CBL10 in Na+ homeostasis regulation, this study indicates that NtCBL10 is a key component in regulating multiple aspects of ion homeostasis under salt stress.