Classification of Calcium-Dependent Protein Kinases and Their Transcriptional Response to Abiotic Stresses in Halophyte Nitraria sibirica

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Calcium-dependent protein kinases (CDPKs) are key Ca2+ sensors in plants, mediating responses to abiotic stresses via phosphorylation signaling. In the halophyte Nitraria sibirica, which thrives in saline soils, we identified 19 CDPK genes (NsCDPKs) and classified them into four canonical angiosperm clades, highlighting conserved functional modules. Promoter analysis revealed diverse cis-acting elements responsive to light, hormones (ABA, MeJA, auxin, GA, SA), and abiotic stresses (drought, cold, wounding), along with numerous MYB binding sites, suggesting complex transcriptional regulation. Transcriptome profiling under salt stress (100 and 400 mM NaCl) showed induction of most NsCDPKs, with several genes significantly upregulated in roots and stems, indicating coordinated whole-plant activation. These salt-responsive NsCDPKs were also upregulated by cold but repressed under PEG-simulated drought, indicating stress-specific regulatory patterns. Fifteen MYB transcription factors, differentially expressed under salt stress, were predicted to interact with NsCDPK promoters, implicating them as upstream regulators. This study identified a potential salt- and cold-responsive CDPK regulatory module and a MYB-mediated transcriptional hierarchy in N. sibirica, providing insights into the molecular mechanisms of salinity adaptation and highlighting candidate genes that could be explored for improving salt tolerance in crop species.