Integrated Transcriptome and Metabolome Analysis Revealed That Flavonoid Biosynthesis May Dominate the Resistance of Zanthoxylum bungeanum against Stem Canker

Stem canker of Zanthoxylum bungeanum is a devastating disease that seriously affects the plantation and industrial development of Z. bungeanum due to a lack of effective control measures. The objective of this study was to screen out resistant Z. bungeanum varieties and further explore their resistance mechanisms against stem canker. Results showed that the most resistant and susceptible varieties were, respectively, Doujiao (DJ) and Fengxian Dahongpao (FD). Combining transcriptomic and metabolomic analyses, we found that the genes and metabolites associated with the phenylpropanoid metabolism, especially flavonoid biosynthesis, were highly significantly enriched in DJ following pathogen infection compared with that in FD, which indicated that the flavonoid metabolism may positively dominate the resistance of Z. bungeanum. This finding was further confirmed by quantitative real-time polymerase chain reaction analysis, through which higher expression levels of core genes involved in flavonoid metabolism in resistant variety were observed. Moreover, by analyzing the differences in the flavonoid content in the stems of resistant and susceptible varieties and the antifungal activities of flavonoids extracted from Z. bungeanum stems, the conclusion that flavonoid metabolism positively regulates the resistance of Z. bungeanum was further supported. Our results not only aid in better understanding the resistance mechanisms of Z. bungeanum against stem canker but also promote the breeding and utilization of resistant varieties.