CIPK9 targets VDAC3 and modulates oxidative stress responses in Arabidopsis

Calcium (Ca²⁺ ) is widely recognized as a key second messenger in mediating various plant adaptive responses. Here we show that calcineurin B-like interacting protein kinase CIPK9 along with its interacting partner VDAC3 identified in the present study are involved in mediating plant responses to methyl viologen (MV). CIPK9 physically interacts with and phosphorylates VDAC3. Co-localization, co-immunoprecipitation, and fluorescence resonance energy transfer experiments proved their physical interaction in planta. Both cipk9 and vdac3 mutants exhibited a tolerant phenotype against MV-induced oxidative stress, which coincided with the lower-level accumulation of reactive oxygen species in their roots. In addition, the analysis of cipk9vdac3 double mutant and VDAC3 overexpressing plants revealed that CIPK9 and VDAC3 were involved in the same pathway for inducing MV-dependent oxidative stress. The response to MV was suppressed by the addition of lanthanum chloride, a non-specific Ca²⁺ channel blocker indicating the role of Ca²⁺ in this pathway. Our study suggest that CIPK9-VDAC3 module may act as a key component in mediating oxidative stress responses in Arabidopsis.