Comprehensive analysis of calcium-dependent protein kinase genes reveals the potential role of PeCDPK32 in lignin biosynthesis of Phyllostachys edulis

Calcium-dependent protein kinases (CDPKs/CPKs) represent a specialized class of Ca²⁺ sensor proteins that decode intracellular calcium fluctuations and translate these signals into phosphorylation cascades, ultimately modulating downstream gene expression. Despite their established roles in model plant species, the functional characterization of CDPKs in moso bamboo (Phyllostachys edulis) - particularly their involvement in the lignification process of this economically important non-timber forest species - remains largely unexplored. In this study, we identified 50 PeCDPK genes through genome-wide analysis and conducted comprehensive characterization of their phylogenetic relationships, conserved domain architectures, gene structure organization, syntenic conservation patterns, and cis-regulatory element composition. Expression profiling demonstrated both tissue-specific patterns and a striking correlation between PeCDPK32 expression and lignification progression in developing bamboo shoots, as confirmed by integrated transcriptomic and qRT-PCR analyses. Through yeast two-hybrid screening, 50 proteins interacting with PeCDPK32 were identified, including the calmodulin-binding protein PeCML4 and the lignin-biosynthetic peroxidase PePRX2. Subcellular localization analysis demonstrated that both PeCDPK32 and PePRX2 localized to the endoplasmic reticulum (ER). Transient overexpression of PeCDPK32 in Nicotiana benthamiana significantly enhanced PePRX2 enzymatic activity, while stable transformation in P. edulis calli promoted lignin biosynthesis. Two autophosphorylation sites on PeCDPK32 were identified by IP-MS analysis. This study presents a systematic genomic and functional characterization of the CDPK gene family in P. edulis, identifying PeCDPK32 as a central regulator of lignin biosynthesis that modulates the lignification pathway through its interaction with key enzymes in the lignification pathway.