The calcium-dependent protein kinases AtCPK4,5,6,11,12 function as positive regulators of thermomorphogenesis in Arabidopsis thaliana

Abstract

CALCIUM-DEPENDENT PROTEIN KINASES (CDPKs/CPKs) are central components in plant signaling networks, orchestrating growth, development, and stress responses. However, their functions in thermomorphogenesis-an essential thermal-adaptation response-particularly their coordination with the core transcription factors PHYTOCHROME-INTERACTING FACTORs 4 and 7 (PIF4 and PIF7), remains elusive. Here we show that AtCPK4/5/6/11/12 physically interact with PIF4 and PIF7. AtCPK4/5/6/11/12 multi-mutants-including triple (cpk4-1cpk5-1cpk6-3 and cpk5-1cpk6-3cpk11-2) and quadruple (cpk4-1cpk5-1cpk6-3cpk11-2) lines-exhibit shortened hypocotyls at 28 °C, indicating a positive role of AtCPK4/5/6/11/12 in thermomorphogenesis. High ambient temperature enhances protein stability of PIF4. Paradoxically, CPKs attenuate PIF4-mediated transcriptional activation in reporter assays, suggesting that CPKs may differentially influence PIF4 at the levels of protein stability and transcriptional activity to fine-tune thermomorphogenesis. RNA-seq analysis further reveals that AtCPK4/5/6/11/12 and PIF4 coordinately regulate a subset of thermomorphogenesis- and cell elongation-related genes. These results highlight a previously uncharacterized CPK4/5/6/11/12-PIF4/7 regulatory module that integrates warm temperature with transcriptome reprogramming in Arabidopsis, providing insights into the regulatory coordination between calcium signaling and thermomorphogenesis.

Keywords: CPK; PIF4/PIF7; Thermomorphogenesis.