Comparative Transcriptomics and Proteomics Analyses of Leaves Reveals a Freezing Stress-Responsive Molecular Network in Winter Rapeseed (Brassica rapa L.)

Winter rapeseed is susceptible to low temperature during winter in Northwest China, which could lead to a severe reduction of crop production. The freezing temperature could stress the whole plant, especially the leaf, and ultimately harm the survival rate of winter rapeseed. However, the molecular mechanism underlying freezing tolerance is still unclear in winter rapeseed. In this study, a comprehensive investigation of winter rapeseed freezing tolerance was conducted at the levels of transcript, protein, and physiology and biochemistry, using a pair of freezing-sensitive and freezing-resistant cultivars NQF24 and 17NTS57. There were 4,319 unique differentially expressed genes (DEGs) and 137 unique differentially abundant proteins (DAPs) between two cultivars identified in leaf under freezing stress. Function enrichment analysis showed that most of the enriched DEGs and DAPs were involved in plant hormone signal transduction, alpha-linolenic/linoleic acid metabolism, peroxisome, glutathione metabolism, fatty acid degradation, and secondary metabolite biosynthesis pathways. Based on our findings, it was speculated that freezing tolerance formation is caused by increased signal transduction, enhanced biosynthesis of protein, secondary metabolites, and plant hormones, elevated energy supply, greater reactive oxygen species scavenging, and lower lipid peroxidation as well as stronger cell stability in leaf under freezing stress. These results provide a comprehensive profile of leaf response under freezing stress, which have potential to be used as selection indicators of breeding programs to improve freezing tolerance in rapeseed.