Comparative Transcriptome Profiling Reveals Differential Defense Responses of Resistant and Susceptible <i>Phalaenopsis</i> to <i>Dickeya fangzhongdai</i>

Soft rot caused by <i>Dickeya fangzhongdai</i> is a destructive disease in <i>Phalaenopsis</i> production that seriously impacts the quality and yield of <i>Phalaenopsis</i>. To explore the molecular mechanisms underlying disease resistance, transcriptome analysis was conducted on resistant and susceptible <i>Phalaenopsis</i> varieties. By comparing the transcriptomes of the resistant variety ‘ES L20’ and the susceptible variety ‘Zishuijing’ after <i>D. fangzhongdai</i> infection, Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analyses were performed. The results revealed that the differentially expressed genes were mainly enriched in pathways related to plant–pathogen interaction, plant hormone signal transduction, and the phenylpropanoid biosynthetic pathway. In the resistant variety ‘ES L20’, some genes in the Ca²⁺ pathway, PAMP-triggered immunity pathway, and Effector-triggered immunity pathway were significantly up-regulated. Analysis of the transcriptome levels of genes in the phytohormone-related pathways showed that genes associated with IAA (indole-3-acetic acid), salicylic acid, and jasmonic acid signal transduction pathways were all up-regulated in the resistant variety after inoculation. Furthermore, the analysis of genes in the phenylpropanoid biosynthesis pathway demonstrated significant up-regulation in the resistant variety. The determination of lignin content validated this result, confirming the crucial role of lignin synthesis in <i>Phalaenopsis</i> defense against soft rot. These findings suggest that the differentially expressed genes in phytopathogenic interaction pathways, along with those involved in hormone-related and lignin synthesis pathways, play important roles in <i>Phalaenopsis</i> resistance to soft rot. This study provides valuable insights into the molecular basis of <i>Phalaenopsis</i> resistance to soft rot and may contribute to the development of effective disease control strategies.