Gene Expression Analysis in Response to Vernalization in Chinese Cabbage (Brassica rapa L.)

Chinese cabbage (Brassica rapa L. var. pekinensis) is an economically and agriculturally significant leafy vegetable that is extensively cultivated throughout the world. Vernalization is exposure to prolonged cold that alters gene expression and accelerates a transition from the vegetative to reproductive phase. Premature bolting caused by exposure to cold inhibits head production and reduces the yield of Chinese cabbage, and developing a late bolting line is important for breeding. Therefore, it is critical to identify the genes showing differential expression patterns during cold treatment in Chinese cabbage. However, there are few studies on the transcriptome profiling of different durations of cold treatments in Chinese cabbage. Here, we analyzed the gene expression profiles in a Chinese cabbage inbred line, RJKB-T24, given different durations of cold treatments using RNA sequencing. Differentially expressed genes (DEGs) between non-vernalized and vernalized samples tended to be downregulated, and some genes involved in the flowering pathway (including BrFLC and BrMAF genes) were downregulated following cold treatment. Functional enrichment analysis indicated that some DEGs were involved in the stress response and hormone signaling pathways. For genes involved in the FRI-containing complex, a known activator of FLC in Arabidopsis thaliana, only BrFRL1 showed changes in expression. In contrast to A. thaliana, BrVIP and BrVRN genes showed different expression patterns between paralogs during cold treatment, suggesting that Chinese cabbage’s flowering pathway is somehow different and more complex than in A. thaliana. These outcomes provide significant insights into the genetic control of bolting and flowering that occur during the vernalization of Chinese cabbage.