Translocation of PpNPR1 is required for β-aminobutyric acid-triggered resistance against Rhizopus stolonifer in peach fruit

This study attempted to determine the transcriptomic responses of peach fruit to beta-aminobutyric acid (BABA) elicitation and Rhizopus stolonifer inoculation and to identify the key differentially expressed genes (DEGs) and significantly enriched pathways between BABA + inoculation-versus-control and inoculation-versus-control pairwise comparisons. Furthermore, the regulatory linkage between the critical DEGs and their interacting proteins was investigated based on the expression of pathogenesis-related (PR) genes in the BABA-treated samples. The results showed that the transcription factor PpTGA1 possessed the highest degree in the protein-protein interaction (PPI) network and was identified as a critical DEG. PpTGA1 could directly interact with the significantly expressed PpNPR1 gene in the nucleus through the salicylic acid (SA)-dependent signalling pathway, eventually leading to high transcript levels of PpPR1 and PpPR1-like. In addition, an increased generation of redox signalling molecules (nitric oxide (NO) and SA) was accompanied by an obvious effect on the suppression of Rhizopus rot in peaches pretreated with BABA and subsequent R. stolonifer challenge. Thus, BABA elicitation and subsequent R. stolonifer inoculation positively modulated the intercellular redox state and consequently induced the translocation of the product of the highly expressed PpNPR1 gene to the nucleus, where it interacts with PpTGA1 and eventually strengthens defence-related gene expression and disease resistance.