A comparative transcriptome analysis of freezing stress responses in early-maturing rapeseed (Brassica napus L.) seedlings.

Rapeseed (Brassica napus L.) is one of most vital oil crops in China, and its cultivation in southern regions is crucial for national edible oil security. However, delayed sowing in southern rice-rapeseed rotation systems exposes seedlings to subzero freezing events, which can cause severe foliar wilting, root injury, and mortality, thereby limiting overwintering survival and yield potential. To address this challenge, enhancing varietal cold tolerance is essential. This study evaluated two early-maturing rapeseed germplasms YLS145 (cold-sensitive) and YLS449 (cold-tolerant) under -4°C freezing treatment for 5 h at the three-leaf stage. The survival rate of the cold-tolerant germplasm YLS449 was significantly higher than that of the cold-sensitive germplasm YLS145, attributable to the rapid response of its antioxidant system. Transcriptome analysis indicated that freezing stress primarily impairs rapeseed physiology by disrupting the photosynthetic system and redox homeostasis. The YLS449 likely activates CBFs centered regulatory network through cold sensing, integrating Reactive Oxygen Species (ROS), circadian, calcium, and hormone signals (jasmonic acid (JA) and abscisic acid (ABA)) into a complex signaling network that enhances freezing tolerance. These findings establish a molecular foundation for cold adaptation mechanisms in early-maturing B. napus.