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 de-hydrogenase (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 con-tent, thereby improving the disease resistance of peach fruit.

Automated summary

Antagonistic yeasts, such as Pichia guilliermondii, can enhance the disease resistance of harvested fruit by regulating the transcription of lignin biosynthesis genes. In this study, P. guilliermondii treatment increased the activities and expression of C4H, CAD, and POD enzymes, as well as the lignin content in peach fruit infected with R. stolonifer. Transcriptome analysis revealed that PpMYB306, a MYB transcription factor, negatively regulated the expression of lignin biosynthesis genes by binding to their promoters. Overexpression of PpMYB306 decreased lignin content and increased the susceptibility of peach fruit to soft rot. Overall, these findings highlight the importance of P. guilliermondii treatment in enhancing disease resistance in peach fruit through the regulation of lignin biosynthesis.