Investigating the Response Mechanism of Weeping Forsythia to Stem Rot Caused by <i>Phomopsis velata</i> Using Transcriptomics

<i>Forsythia</i> <i>suspensa</i> is an important ornamental horticultural plant, and its fruit is a traditional Chinese medicine used for treating inflammation and pyrexia. <i>Phomopsis velata</i> is a pathogen causing stem rot disease in <i>F</i>. <i>suspensa</i>. In this study, we investigated the host-response mechanism of healthy forsythia plants inoculated with <i>P</i>. <i>velata</i> by evaluating physiological indexes, hormone content, and gene expression levels 5, 10, and 15 days postinoculation. After inoculation with <i>P</i>. <i>velata</i> on forsythia branches, the symptoms of stem rot disease appeared. The activity of physiological indexes and hormone content were significantly changed. Compared with the control groups, 1,112 genes were significantly changed at transcriptional levels in treatment groups. The results of Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analysis showed that differently expressed genes were mainly enriched in plant-pathogen interaction, plant hormone signal transduction, the MAPK signaling pathway, and the peroxidase pathway. The plant-pathogen interaction pathway exhibited the most enriched differentially expressed genes. Our study has identified <i>CaMCML</i>, <i>FLS2</i>, <i>EIX1/2</i>, <i>BAK1</i>, and other related protein receptors. This study elucidates the molecular defense mechanisms of <i>F</i>. <i>suspensa</i> in response to <i>P</i>. <i>velata</i> infection, providing a theoretical foundation for the effective management of stem rot disease in this species.