PpWRKY22 physically interacts with PpHOS1/PpTGA1 and positively regulates several SA-responsive PR genes to modulate disease resistance in BABA-primed peach fruit

Abstract

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.