Functional insights into avrPto5 from Pseudomonas syringae pv. actinidiae and its interaction with zinc finger proteins regulating plant defenses

Pseudomonas syringae pv. actinidiae is a significant pathogen affecting kiwifruit, with varying degrees of virulence among its strains. These pathogenic bacteria use type III effector proteins (T3Es) as essential virulence factors to suppress host immunity and cause disease. However, in many cases, the molecular function of T3Es remains less studied. In this study, a deletion of the effector protein AvrPto5 with the P. syringae pv. actinidiae wild-type strain G1 was compared to decode its pathogenic mechanisms. Upon infiltration into leaves and branches of the kiwifruit cultivar “Hongyang”, the ΔavrPto5 knockout mutant strain exhibited increased lesion lengths and larger disease areas compared to the wild-type strain G1, indicating enhanced virulence due to the mutation. Further investigation into kiwifruit genome mediated library screening through yeast two-hybrid (Y2H) indicated direct interactions between avrPto5 and two stress associated proteins (SAP) of kiwifruit host, KWSAP5 and KWML3, and validated by GST pull-down assays. This work was primarily focused on KWSAP5, a member of the A20/AN1 zinc finger protein family, closely related to AT3G12630 in Arabidopsis thaliana, containing conserved Znf-A20 and zf-AN1 domains and involved in oxidative stress and resistance against P. syringae infection. Y2H and GST-pull-down assays underscore avrPto5 role in modulating host-pathogen interactions, where its absence may disrupt normal immune signaling pathways, leading to increased pathogenicity. This study enhances the understanding of the molecular determinants of P. syringae pv. actinidiae virulence and emphasizes the critical interaction between avrPto5 and host SAP proteins, presenting potential targets for the development of resistant kiwifruit cultivars.