PpMYB44 positively affects salicylic acid biosynthesis in Pichia guilliermondii-induced peach fruit resistance against Rhizopus stolonifer

Antagonistic yeast induces postharvest disease resistance and delays fruit decay. Salicylic acid (SA), a signal molecule, is required for activating induced disease resistance in various harvested fruit. However, there is limited information about the transcriptional regulatory mechanism of SA biosynthesis in response to Rhizopus stolonifer in peaches. Our results showed that Pichia guilliermondii application promoted SA accumulation accompanied by increasing SA biosynthetic enzyme activity of PAL and ICS and upregulating transcripts of SA synthesis-related genes and defense genes, including PpPAL1, PpPAL2, PpICS1, PpICS2, PpCM1, PpCM2, PpCM3, PpBA2H, PpSARD1, PpCBP60g, PpPR1, PpPR2, and PpPR5. In addition, an R2R3 MYB transcription factor, PpMYB44, was induced in P. guilliermondii-peach fruit in response to fungal disease, and PpMYB44 was identified to mediate SA synthesis by binding to the promoters of PpPAL1 and PpSARD1. Furthermore, the transient overexpression of PpMYB44 in peach fruit reduced disease incidence and severity, upregulated the expression of SA synthesis-related genes (PpPAL1 and PpSARD1) and enhanced SA accumulation. Silencing of PpMYB44 in peach fruit increased disease incidence and severity, downregulated the transcript levels of PpPAL1 and PpSARD1, and decreased SA accumulation. Thus, the study indicates that PpMYB44 regulates yeast-induced disease resistance by increasing the SA content in peaches.