Search

WRKY transcription factors (TFs) are essential for the regulation of disease resistance in plants, and ubiquitination is one of the major post-translational modification types for a suite of TFs, while limited information is available about the involvement of E3 ubiquitin ligase-mediated regulation of WRKY proteins in β-amino-butyric acid (BABA)-primed defense resistance in peach fruit. Here, we observed that the treatment of peach fruit with BABA elicited disease resistance against the necrotrophic fungus Rhizopus stolonifer, resulting in an obvious inhibition of Rhizopus rot, which was accompanied by accumulation of total phenolics and lignins and potentiated the activity of several defensive enzymes, including phenylalanine ammonia-lyase (PAL), chitinase (CHI) and β-1,3-glucanase (GNS). Additionally, the expression of PpHOS1 that encodes a C3HC4-type Really Interesting New Gene (RING) finger E3 ligase was induced in BABA-treated peach fruit in response to R. stolonifer attack, following which the specific PpWRKY22 protein was exclusively targeted by PpHOS1 for possible degradation. Notably, PpWRKY22 functions as a positive regulator in disease resistance, as determined by overexpression of PpWRKY22 in Arabidopsis thaliana, which conferred enhanced resistance to the fungus R. stolonifer. Moreover, the physical interaction between PpWRKY22 and PpTGA1 increased the transactivation of PpNPR1, PpPR1, PpPR2, and PpPR5 by PpWRKY22 alone, leading to elevated resistance of peach fruit against the fungus R. stolonifer. Taken together, our results indicated that PpWRKY22 might be a positive participant in BABA-primed resistance in peach fruit, which could involve the post-translational ubiquitination of PpWRKY22 by PpHOS1 and physical interaction between PpWRKY22 and PpTGA1 for modification and activation.

This study attempted to determine the transcriptomic responses of peach fruit to β-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.