PpTGA1 Integrates the Salicylic Acid and Jasmonic Acid Signalling Networks to Enhance Resistance to Bacterial Spot Disease in Peach

Salicylic acid (SA) and jasmonic acid (JA) play critical roles in regulating plant disease resistance. However, the underlying molecular mechanisms of their coordinated action against pathogens in woody plants, particularly in peach (Prunus persica), are unknown. In this study, we demonstrate that SA and JA positively regulate resistance to bacterial spot disease induced by Xanthomonas arboricola pv. pruni (Xap) in peach. Two defence-responsive genes, pathogenesis-related protein 2 (PpPR2) and PpPR5, were induced to express during this disease response. A key transcription factor, TGACG-BINDING FACTOR 1 (PpTGA1), functioned as a positive regulator of disease resistance by activating PpPR2 and PpPR5 transcription. Furthermore, nonexpressor of pathogenesis-related gene 1 (PpNPR1), a core component of the SA signalling response pathway, interacted with PpTGA1 to enhance transcriptional activation of PpTGA1 on downstream PR genes, thereby strengthening disease resistance. The JA signalling repressor, JASMONATE ZIM-DOMAIN 1 (PpJAZ1), negatively regulated disease resistance by interacting with PpTGA1 and inhibiting its transcriptional activation on the PRs. In summary, this study reveals an important regulatory network mediated by SA-JA hormone crosstalk for peach resistance to bacterial spot disease, based on the PpNPR1/PpJAZ1-PpTGA1-PpPR2/5 cascade. These findings provide novel insight into the synergistic crosstalk between hormones and the defence mechanisms against bacterial spot disease.