Transcriptomic analysis of resistant and susceptible cabbage lines reveals differential expressions and candidate genes involved in cabbage early responses to black rot

Cabbage (Brassica oleraceavar. capitata) is one of the most important cruciferous leafy vegetable crops and is widely cultivated all over the world. Its yield and quality are often affected by diseases such as cabbage black rot. 2R is a cabbage line that is newly resistant to black rot, which was created by radiation mutagenesis and backcross transfer. However, the underlying molecular bases and mechanisms of early-phase response of different resistant cabbage lines against black rot infections remain unknown. Here, we completed a comprehensive transcriptome profile analysis between resistant (2R) and susceptible (2T) cabbage lines after black rot inoculations. The results showed that the typical V-shaped lesions were found in inoculated plants after 15 days, and the symptoms in the susceptible cabbage lines (2T) were significant severe than that of the resistant 2R line. A total of 10,030 differentially expressed genes (DEGs) were identified, of which 384 DEGs were found to overlap in resistant and susceptible cabbage lines after black rot infections, suggesting those DEGs may play more important roles in cabbage early responses to black rot infections. We ranked the expression levels of DEGs among the four comparison sets of resistant and susceptible cabbage lines and, interestingly, found the top ten differential expression genes contained NBS-LRR genes, protein kinase genes and expansin genes. These findings provide a comprehensive differential transcriptome profile between resistant and susceptible cabbage lines and indicate some genes play key roles in the regulation of early response to black rot infections, which will help to understand the molecular resistance of cabbage against these infections.