Integrated Transcriptome and Metabolome Analysis Reveals the Molecular Mechanism of Resistance (Youkang) and Susceptive (Tengjiao) <em>Zanthoxylum armatum</em> Cultivars Rust

Chinese pepper rust is a live parasitic fungal disease caused by Coleosporium zanthoxyli, which seriously affects the cultivation and industrial development of Z. armatum. Cultivating and planting resistant cultivars is considered the most economical and environmentally friendly strategy to control this disease. Therefore, the mining of excellent genes for rust resistance and analysis of the mechanism of rust resistance are the key strategies to achieve the targeted breeding of rust resistance. However, there is no relevant report on pepper rust resistance at present. The aim of the present study was to further explore the resistance mechanism of pepper by screening the rust-resistant germplasm resources in the early stage. Combined with the analysis of plant pathology, transcriptomics, and metabolomics, we found that the genes and metabolites related to phenylpropanoid metabolism were highly enriched in resistant varieties after pathogen infection, which indicated that phenylpropanoid metabolism might mediate the resistance of Z. armatum. This finding was further confirmed by real-time quantitative polymerase chain reaction analysis, which revealed that the expression levels of core genes involved in phenylpropane metabolism in disease-resistant varieties were high. In addition, the difference in flavonoid content in the leaves between resistant and susceptible varieties further supported the conclusion that the flavonoid pathway is one of the main pathways involved in resistance formation in Chinese pepper, and MeJA is involved in the formation of resistance. Our research results not only help to better understand the resistance mechanism of Z. armatum rust but also contribute to the breeding and utilization of resistant varieties.