OsSARD1 Orchestrates the Ca²⁺/OsCaM1‐Guided Transcriptional Regulation of <i>OsDREB1A</i>/<i>1B</i>/<i>1H</i> Regulons Under Chilling in Rice

The Ca²⁺/calmodulins (CaMs) mediate the signalling in chilling in plants. However, how SAR Deficient 1 (SARD1), a Ca²⁺/CaMs-regulated CALMODULIN-BINDING PROTEIN 60 (CBP60) family protein, regulates the CBF/DREB1 regulon in the chilling response remains unknown in rice. Here, transgenics experiments identified the positive regulation of OsSARD1, OsCaM1-1 and OsDREB1A/1B/1H to chilling in rice seedlings. Furthermore, the in vitro and in vivo interaction assays demonstrated that OsSARD1 was specifically interacted with OsCaM1 in the nucleus of rice cells. OsCaM1 guided the transcriptional activation of OsSARD1 to the downstream targets OsDREB1A/1B/1H through binding to the GAAATTT motif of their promoters in chilling. Genome-wide transcriptomic screening revealed that OsSARD1 and OsDREB1 coregulated 135 cold-regulated (COR) genes with the C-repeat/dehydration-responsive (CRT/DRE) motif in their promoters. These new results indicate that OsCaM1 can interact with and enhance the transcriptional activity of OsSARD1 to the downstream targets OsDREB1A/1B/1H, thus regulating the DREB1s regulons in chilling. Therefore, our findings reveal a novel OsCaM1-OsSARD1-OsDREB1A/1B/1H module in chilling response and a promising genetic engineering application for chilling tolerance in rice.