PLATZ2 negatively regulates salt tolerance in Arabidopsis seedlings by directly suppressing the expression of the CBL4/SOS3 and CBL10/SCaBP8 genes

Although the salt overly sensitive (SOS) pathway plays essential roles in conferring salt tolerance in Arabidopsis thaliana, the regulatory mechanism underlying SOS gene expression remains largely unclear. In this study, AtPLATZ2 was found to function as a direct transcriptional suppressor of CBL4/SOS3 and CBL10/SCaBP8 in the Arabidopsis salt stress response. Compared with wild-type plants, transgenic plants constitutively overexpressing AtPLATZ2 exhibited increased sensitivity to salt stress. Loss of function of PLATZ2 had no observed salt stress phenotype in Arabidopsis, while the double mutant of PLATZ2 and PLATZ7 led to weaker salt stress tolerance than wild-type plants. Overexpression of AtPLATZ2 in transgenic plants decreased the expression of CBL4/SOS3 and CBL10/SCaBP8 under both normal and saline conditions. AtPLATZ2 directly bound to A/T-rich sequences in the CBL4/SOS3 and CBL10/SCaBP8 promoters in vitro and in vivo, and inhibited CBL4/SOS3 promoter activity in the plant leaves. The salt sensitivity of #11 plants constitutively overexpressing AtPLATZ2 was restored by the overexpression of CBL4/SOS3 and CBL10/SCaBP8. Salt stress-induced Na+ accumulation in both the shoots and roots was more exaggerated in AtPLATZ2-overexpressing plants than in the wild type. The salt stress-induced Na+ accumulation in #11 seedlings was also rescued by the overexpression of CBL4/SOS3 and CBL10/SCaBP8. Furthermore, the transcription of AtPLATZ2 was induced in response to salt stress. Collectively, these results suggest that AtPLATZ2 suppresses plant salt tolerance by directly inhibiting CBL4/SOS3 and CBL10/SCaBP8, and functions redundantly with PLATZ7.