AP2C1 dephosphorylates CIPK9 to negatively regulate its function in controlling root growth and seedling development under low-K+ conditions in Arabidopsis.

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Voltage-dependent anion channels (VDACs) are conserved proteins of the mitochondria. We have functionally compared Arabidopsis VDACs using Saccharomyces cerevisiae Dpor1 and M3 yeast system. VDAC (1, 2, and 4) were able to restore Dpor1 growth in elevated temperature, in oxidative and salt stresses, whereas VDAC3 only partially rescued Dpor1 in these conditions. The ectopic expression of VDAC (1, 2, 3, and 4) in mutant yeast recapitulated the mitochondrial membrane potential thus, enabled it to maintain reactive oxygen species homeostasis. Overexpression of these VDACs (AtVDACs) in M3 strain did not display any synergistic or antagonistic activity with the native yeast VDAC1 (ScVDAC1). Collectively, our data suggest that Arabidopsis VDACs are involved in regulating respiration, reactive oxygen species homeostasis, and stress tolerance in yeast.

Just like animals, plants also contain haemoglobins (known as phytoglobins in plants). Plant phytoglobins (Pgbs) have been categorized into 6 different classes, namely, Phytogb0 (Pgb0), Phytogb1 (Pgb1), Phytogb2 (Pgb2), SymPhytogb (sPgb), Leghaemoglobin (Lb), and Phytogb3 (Pgb3). Among the 6 Phytogbs, sPgb and Lb have been functionally characterized, whereas understanding of the roles of other Pgbs is still evolving. In our present study, we have explored the function of 2 rice Pgbs (OsPgb1.1 and OsPgb1.2). OsPgb1.1, OsPgb1.2, OsPgb1.3, and OsPgb1.4 displayed increased level of transcript upon salt, drought, cold, and ABA treatment.The overexpression (OX) lines of OsPgb1.2 in Arabidopsis showed a tolerant phenotype in terms of better root growth in low potassium (K + ) conditions. The expression of the known K + gene markers such as LOX2, HAK5, and CAX3 was much higher in the OsPgb1.2 OX as compared to wild type. Furthermore, the OsPgb1.2 OX lines showed a decrease in reactive oxygen species (ROS) production and conversely an increase in the K + content, both in root and shoot, as compared to wild type in K + limiting condition. Our results indicated the potential involvement of OsPgb1.2 in signalling networks triggered by the nutrient deficiency stresses.

Calcium (Ca 2+ ) 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 Ca 2+ channel blocker indicating the role of Ca 2+ in this pathway. Our study suggest that CIPK9-VDAC3 module may act as a key component in mediating oxidative stress responses in Arabidopsis.

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