Abstract
BACKGROUND: Flower blight is a fungal disease that significantly compromises the ornamental value of Rhododendron petals. However, the molecular mechanisms underlying the interaction between Rhododendron petals and pathogens remain poorly understood. To investigate the defense responses of Rhododendron hybridum petals to pathogenic infection, this study employed transcriptomic and widely targeted metabolomic approaches to analyze constitutive metabolites differences between the resistant cultivar Rhododendron hybridum 'Yangmeihong' (YMH) and the susceptible cultivar 'Xiaotaohong' (XTH), as well as changes in gene expression and metabolite accumulation following infection with Neopestalotiopsis clavispora. RESULTS: A total of 144 constitutive metabolites were identified in YMH petals, whereas 131 were upregulated in XTH petals, suggesting these metabolites may serve as part of the first line of defense during early pathogen infection. At 2 days post-inoculation (dpi), differentially expressed genes (DEGs) in YMH were predominantly enriched in pathways related to amino acid metabolism, central carbon and energy metabolism, nucleotide and sugar metabolism, defense metabolism, and photosynthetic metabolism. In contrast, DEGs in XTH were enriched in pathways secondary metabolite biosynthesis, antioxidant and redox metabolism, and cell structure and motility pathways. Overall, 612 metabolites were identified across both cultivars. Among them, 38 differentially accumulated metabolites (DAMs) were specifically induced in XTH, while 28 were specifically induced in YMH. Integrated transcriptomic and metabolomic analysis revealed that the plant hormone signal transduction pathway likely plays distinct roles in mediating the immune responses of the two cultivars to pathogen infection. CONCLUSIONS: These findings enhance our understanding of the moleculer mechanisms governing the interaction between Rhododendron petals and pathogens and provide new insights into the genetic and metabolic basis of disease resistance in Rhododendron.