Comparative transcriptomic and biochemical analyses reveal candidate regulatory genes associated with early drought response signatures in contrasting rapeseed (Brassica napus) cultivars

Drought stress triggers complex and multilayered physiological, biochemical, and molecular responses contributing to plant stress adaptation mechanisms. In this study, we performed comparative transcriptomic and biochemical analyses between drought-tolerant and drought-sensitive rapeseed (Brassica napus) cultivars to identify candidate early response regulatory genes and molecular pathways associated with enhanced response to drought at the seedling stage. Under drought stress, the tolerant cultivar exhibited higher relative water content, greater proline accumulation, elevated antioxidant enzyme activities, and reduced membrane damage compared to the sensitive cultivar. Transcriptomic profiling revealed distinct early-response gene expression signatures between the cultivars. The cultivar-specific expression patterns of the candidate regulatory genes encoding transcription factors (DREB2A, ABI5, NAC019, ZAT10, MYB15, MYB44), protein kinases (SRK2E, SRK2I), calmodulin-like proteins (CML37, CML40), components of the ubiquitin-proteasome system (RDUF2, PUB23), along with drought-responsive effector genes (NCED3, RD29B, HAI1) may facilitate early activation of abscisic acid (ABA) and calcium signaling pathways, enhance activities of antioxidant enzymes and reactive oxygen species (ROS) detoxification, promote proline accumulation, and potentially improve the efficiency of protein degradation and turnover in the drought-tolerant cultivar. Together, these findings provide valuable insights into candidate genes and regulatory pathways associated with enhanced early drought responses in rapeseed, offering potential targets for genetic improvement through molecular breeding technologies.