Bacterial fruit blotch (BFB) is a disease of cucurbit plants caused by Acidovorax citrulli. Although A. citrulli has great destructive potential, the molecular mechanisms of pathogenicity of A. citrulli are not clear, particularly with regard to its type III secreted effectors. In this study, we characterized the type III secreted effector protein, AopV, from A. citrulli strain Aac5. We show that AopV significantly inhibits reactive oxygen species and the expression of PTI marker genes, and helps the growth of Pseudomonas syringae D36E in Nicotiana benthamiana. In addition, we found that the aromatic dehydratase ADT6 from watermelon was a target of AopV. AopV interacts with ADT6 in vivo and in vitro. Subcellular localization indicated ADT6 and AopV were co-located at the cell membrane. Together, our results reveal that AopV suppresses plant immunity and targets ADT6 in the cell membrane. These findings provide an new characterization of the molecular interaction of A. citrulli effector protein AopV with host cells.

SGT1 (the suppressor of the G2 allele of Skp1) functions as an adaptor protein that positively regulates plant defense and developmental processes. It comprises three functional domains: the tetratricopeptide repeat (TPR) domain, Chord SGT1 motif (CS), and SGT1-specific motif (SGS). In this study, we resolved the crystal structure of the Oryza sativa OsSGT1-TPR domain at 1.53 Å resolution. Structural analysis showed that the TPR domain adopts a homo-dimeric architecture stabilized by salt bridges (mediated by K52/R79/R109) and hydrophobic interactions (involving F17). Functional validation through gel filtration chromatography revealed that the disruption of the dimerization interface via F17A/K52A/R79A mutations caused complete dissociation into monomers, establishing the essential role of TPR-mediated oligomerization in maintaining the structural stability of full-length OsSGT1. Yeast two-hybrid assays showed that the dimerization disruption of SGT1 mutants retained the interaction with OsHSP81-2 (an HSP90 ortholog) and OsRAR1, indicating that SGT1 oligomerization serves primarily as a structural stabilizer rather than a prerequisite for partner interaction. Evolutionary analysis through the sequence alignment of plant SGT1 proteins revealed the conservation of the dimerization interface residues. This study provides structural insights into the conserved molecular features of SGT1 proteins and highlights the functional significance of their oligomerization state.