Studies of Type III effectors and their impacts on the Ralstonia solanacearum-Tomato Interactions
Creators: name: HS, Huang
name: Oliva R, Lin YR
Publisher: name: World Vegetable Center
Year: 2024
Subjects: subject: BACTERIAL WILT
subject: DEFENSE MECHANISMS
subject: tomato
subject: QUANTITATIVE ANALYSIS
subject: Ralstonia solanacearum species complex (RSSC)
subject: Bacterial wilt
subject: Solanaceous crops
subject: Non-solanaceous crops
subject: Type III effectors (T3Es)
subject: Host defense mechanisms
subject: Tomato plants
subject: T3E repertoire composition
subject: R. solanacearum populations
subject: Virulence evaluation
subject: Tomato accessions
subject: Disease symptoms
subject: Spearman correlation
subject: Positive selection analyses
subject: Candidate T3Es
subject: RipE2
subject: Resistance QTL Brw-12
subject: Bayes empirical Bayes analysis
subject: Amino acid at position 204 (tyrosine, asparagine, histidine)
subject: Disease index (DI)
subject: Pathogenicity
subject: Fitness
subject: Disease management strategies

description: The Ralstonia solanacearum species complex (RSSC) is a devastating bacterial pathogen causing bacterial wilt in various host plants, resulting in substantial economic losses for important solanaceous and non-solanaceous crops. RSSC secretes type III effectors (T3Es) into the plant cell to manipulate host defense mechanisms and facilitate colonization. However, the interactions between RSSC populations and tomato plants, and the impact of T3E repertoire composition across different strains, remain poorly understood. In this study, we identified eight distinct R. solanacearum populations in Taiwan, each with a unique T3E repertoire composition. We evaluated the virulence of these populations by inoculating strains onto a set of tomato accessions with varying resistance profiles. Our results showed that different tomato accessions exhibited diverse disease symptoms, indicating that distinct combinations of T3Es influence interactions with each tomato accession. To investigate type III effectors contributing to virulence in the interaction between R. solanacearum and tomato, Spearman correlation and positive selection analyses were conducted and identified 6 and 15 T3Es, respectively, with significant correlations to tomato disease symptoms and evidence of positive selection. Among these candidate T3Es, RipE2 was notably associated with disease symptoms in tomato accessions carrying the resistance QTL Brw-12 and was also under positive selection, suggesting that RipE2 may possess advantageous alleles that enhance v pathogenicity or fitness. Bayes empirical Bayes analysis revealed 13 sites under moderate positive selection in the RipE2 protein sequence. The amino acid at position 204 of RipE2 is particularly critical for R. solanacearum fitness; tyrosine (Y) at this position correlates with a low disease index (DI), whereas asparagine (N) or histidine (H) is associated with a high DI in tomato phenotypes. This study identified 20 candidate T3Es, with RipE2 emerging as a promising candidate, providing valuable insights into R. solanacearum pathogenesis in tomatoes and offering potential strategies for targeted disease management