Transcriptome Response of <i>Rosa roxburghii</i> Fruit to Top-Rot Disease and Functional Analysis of <i>RrHSP18.1</i> in Top-Rot Disease Resistance

Top-rot disease (TRD) in <i>Rosa roxburghii</i> fruit is caused by <i>Colletotrichum fructicola</i>. TRD has emerged as a significant concern due to its frequent occurrence and causing substantial economic losses. To understand the transcriptome response to TRD infection and identify candidate genes involved in TRD resistance, four critical time points (0, 24, 72, and 120 h postinoculation) for fruit tissues inoculated with the TRD pathogen were selected for RNA sequencing. A total of 1,890 differentially expressed genes were identified from the transcriptome data, including 1,051 upregulated and 839 downregulated genes. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses revealed that they were primarily involved in oxidoreductase activity and the synthesis and metabolism of secondary metabolites. Many putative transcription factor families, such as MYB, bHLH, AP2-EREBP, NAC, and WRKY, were also identified as being positively responsive to TRD infestation. Among the upregulated genes, <i>RrHSP18.1</i> exhibited the strongest response to TRD. Transient overexpression and gene silencing demonstrated that <i>RrHSP18.1</i> positively regulated TRD resistance in <i>R. roxburghii</i> fruit, partially through promoting the expression of antioxidant-related genes and enhancing their enzyme activities. Collectively, the results facilitated a better understanding of the transcriptional response to TRD and offered candidate genes for developing an <i>R. roxburghii</i> germplasm resource with improved TRD resistance.