Abstract:
Drought is a major threat to plant growth and crop productivity. Calcium-dependent protein kinases (CDPKs, CPKs) are
believed to play important roles in plant responses to drought stress. Here, we report that Arabidopsis thaliana CPK8
functions in abscisic acid (ABA)- and Ca2+-mediated plant responses to drought stress. The cpk8 mutant was more sensitive
to drought stress than wild-type plants, while the transgenic plants overexpressing CPK8 showed enhanced tolerance to
drought stress compared with wild-type plants. ABA-, H2O2-, and Ca2+-induced stomatal closing were impaired in cpk8
mutants. Arabidopsis CATALASE3 (CAT3) was identified as a CPK8-interacting protein, confirmed by yeast two-hybrid,
coimmunoprecipitation, and bimolecular fluorescence complementation assays. CPK8 can phosphorylate CAT3 at Ser-261
and regulate its activity. Both cpk8 and cat3 plants showed lower catalase activity and higher accumulation of H2O2 compared
with wild-type plants. The cat3 mutant displayed a similar drought stress-sensitive phenotype as cpk8 mutant. Moreover, ABA
and Ca2+ inhibition of inward K+ currents were diminished in guard cells of cpk8 and cat3 mutants. Together, these results
demonstrated that CPK8 functions in ABA-mediated stomatal regulation in responses to drought stress through regulation of
CAT3 activity.
