Calcium-dependent protein kinase CPK32 mediates calcium signaling in regulating Arabidopsis flowering time

Appropriate flowering time is critical for the reproductive success of plant species. Emerging evidence indicates that calcium may play an important role in the regulation of flowering time. However, the underlying molecular mechanisms remain unclear. In this study, we demonstrate that calcium-dependent protein kinase 32 (CPK32) regulates flowering time by affecting the alternative polyadenylation of FLOWERING CONTROL LOCUS A (FCA) and altering the transcription of FLOWERING LOCUS C (FLC), a central repressor of flowering time. The knockdown of CPK32 results in an obvious late flowering phenotype and dramatically enhanced FLC transcription. CPK32 interacts with FCA, and phosphorylates the serine592 of FCA in a Ca2+-dependent manner. Moreover, the ratio of abundance of the FCA transcripts (FCA-D and FCA-P) changes significantly in the cpk32 mutant, which subsequently affects FLC expression and consequently regulates floral transition. The present evidence demonstrates that CPK32 modulates flowering time by regulating FCA alternative polyadenylation and consequent FLC expression.