Transcriptome and Metaproteome Analysis of Rhododendron hybridum Leaf Defense Responses to Neopestalotiopsis clavispora Infection

Brown leaf spot, a severe fungal disease in Rhododendron, substantially impairs its ornamental and economic value. However, the molecular mechanisms governing the interaction between Rhododendron leaves and the pathogen are still poorly understood. In this study, the less susceptible Rhododendron hybridum ‘Yangmeihong’ (YMH) and the highly susceptible R. hybridum ‘Xiaotaohong’ (XTH) leaves were selected for transcriptomic and widely targeted metabolomic analyses. We compared constitutive metabolite profiles prior to inoculation as well as differentially expressed gene (DEGs) and differentially accumulated metabolites (DAMs) at two days post-inoculation (dpi) with Neopestalotiopsis clavispora. Results showed that YMH leaves exhibited 273 upregulated constitutive metabolites, whereas XTH had only 46. After infection, DEGs in YMH leaves were significantly enriched in pathways including flavonoid biosynthesis and glycerolipid metabolism, while XTH showed enrichment in vitamin B6 metabolism and glutathione metabolism. Metabolomic analysis identified 788 metabolites at 2 dpi, with YMH accumulating 49 DAMs and XTH accumulating 115 DAMs. Integrated transcriptomic and metabolomic analyses further revealed distinctions in reactive oxygen species (ROS) scavenging mechanisms between the two cultivars. These findings offer valuable insights for developing disease-resistant breeding and control strategies in Rhododendron.