Involvement of PpMYB306 in Pichia guilliermondii-induced peach fruit resistance against Rhizopus stolonifer

Antagonistic yeasts are promising agents for inducing host resistance against pathogens in harvested fruit, but the transcriptional regulatory mechanism involved remains unclear. In our study, Pichia guilliermondii treatment increased the enzyme activities and gene expression of cinnamate 4-hydroxylase (C4H), cinnamyl alcohol dehydrogenase (CAD), and peroxidase (POD) and maintained a higher lignin content in peach fruit after R. stolonifer infection. Transcriptome analysis revealed a total of 17 differentially expressed genes (DEGs) encoding MYB transcription factors (TFs); among them, the gene expression of PpMYB306 was downregulated by P. guilliermondii treatment. In addition, by binding to the promoters of PpC4H, PpCAD1, and PpPOD44, PpMYB306 negatively regulated lignin biosynthesis in peach fruit. Furthermore, transient overexpression of PpMYB306 in peach fruit decreased the expression of PpC4H, PpCAD1, and PpPOD44, reducing the lignin content and thus increasing the lesion diameter associated with soft rot. Taken together, these findings suggested that P. guilliermondii treatment inhibited PpMYB306-mediated the transcriptional repression of lignin biosynthesis-related genes in peach fruit after R. stolonifer infection, which contributed to maintaining a higher lignin content, thereby improving the disease resistance of peach fruit.