Transcriptomic analysis reveals differential transcriptional regulation underlying Citrus Bacterial Canker (CBC) tolerance in Citrus sinensis.

The sustainable development of the citrus industry is greatly affected by citrus canker, an important bacterial disease. To explore the transcriptional regulatory mechanism of citrus resistance to canker disease, this study used the susceptible Citrus sinensis cv. 'Newhall' and its citrus canker-resistant bud mutation variety 'Longhuitian' (LHT) as materials. Through analysing the variances in leaf phenotypes between Newhall and LHT, as well as the variations in their transcriptional expression under Xanthomonas citri subsp. citri (Xcc) inoculation, our study concluded that LHT displays markedly greater resistance to Xcc compared to Newhall. Additionally, the spongy parenchyma of LHT leaves is significantly thicker than that of Newhall, and the stomatal number is significantly higher in LHT leaves, while the length and width of individual stomata in LHT leaves are significantly smaller than those in Newhall. RNA-seq analysis indicates that the differentially expressed genes between LHT and Newhall are involved in biotic stress-related biological processes, secondary metabolite biosynthesis, as well as phytohormone signalling pathways. Furthermore, significant differences were observed in reactive oxygen metabolism and phenylalanine metabolism pathways. The findings of our study provide data support for a deeper understanding of the citrus-Xcc interactions and offer valuable clues for unravelling citrus resistance to citrus canker.