Characteristics of putative effectors from Xanthomonas fragariae YL19 and its host targets in strawberry

Abstract Xanthomonas fragariae (Xaf) strain YL19, a newly identified highly virulent strain reported in 2021, not only causes angular leaf spots but also frequently induces severe crown dry cavity rot in strawberry plants, leading to significant economic losses in China in recent years. Similar to other Xanthomonas species, Xaf relies on type III effectors (T3Es) for full virulence. However, the characteristics and functions of T3Es in this pathogen remain poorly understood. In this study, we predicted 33 T3Es based on the annotated genome of Xaf YL19. Among them, the transcript levels of nine effector genes were significantly upregulated during infection in strawberry leaves. Six effectors (XopAE, XopD, XopF1, XopF2, XopX2, and XopH) triggered cell death in Nicotiana benthamiana, while five effectors (AvrBs1, XopQ, XopK, XopE4, and XopAF) completely suppressed BAX-induced cell death in N. benthamiana. Additionally, several effectors were found to localize specifically to the plasma membrane or the chloroplast. We also identified host protein interactors in strawberry plants using a high-throughput yeast two-hybrid system and constructed an interaction network between strawberry proteins and Xaf YL19 effectors. Notably, five effectors (AvrBs1, XopX1, XopL, XopH, and XopC1) interacted with FveACO4-like (1-aminocyclopropane-1-carboxylate oxidase homolog 4-like), which served as a central target hub. This study provides insights into the characteristics of T3Es from Xaf YL19 and their potential host targets.