Loss of Virulence of the Phytopathogen Ralstonia solanacearum Through Infection by φRSM Filamentous Phages

• Published in: Phytopathology 2012-05, Vol.102 (5), p.469-477
• Main Authors: ADDY, Hardian S, ASKORA, Ahmed, KAWASAKI, Takeru, FUJIE, Makoto, YAMADA, Takashi
• Format: Article
• Language: English
• Subjects: Bacterial plant pathogens; Bacterial Proteins - genetics; Biological and medical sciences; Fimbriae Proteins - genetics; Fimbriae, Bacterial - genetics; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Bacterial - genetics; Genes, Bacterial - genetics; Genes, Viral - genetics; Inovirus - genetics; Inovirus - physiology; Lycopersicon esculentum; Lycopersicon esculentum - microbiology; Phytopathology. Animal pests. Plant and forest protection; Plant Diseases - microbiology; Polysaccharides, Bacterial - metabolism; Ralstonia solanacearum; Ralstonia solanacearum - genetics; Ralstonia solanacearum - pathogenicity; Ralstonia solanacearum - physiology; Ralstonia solanacearum - virology; Virulence - genetics; Virulence Factors - genetics
• ISSN: 0031-949X; 1943-7684
• DOI: 10.1094/PHYTO-11-11-0319-R

φRSM1 and φRSM3 (φRSM phages) are filamentous phages (inoviruses) that infect Ralstonia solanacearum, the causative agent of bacterial wilt. Infection by φRSM phages causes several cultural and physiological changes to host cells, especially loss of virulence. In this study, we characterized changes related to the virulence in φRSM3-infected cells, including (i) reduced twitching motility and reduced amounts of type IV pili (Tfp), (ii) lower levels of β-1,4-endoglucanase (Egl) activity and extracellular polysaccharides (EPS) production, and (iii) reduced expression of certain genes (egl, pehC, phcA, phcB, pilT, and hrpB). The significantly lower levels of phcA and phcB expression in φRSM3-infected cells suggested that functional PhcA was insufficient to activate many virulence genes. Tomato plants injected with φRSM3-infected cells of different R. solanacearum strains did not show wilting symptoms. The virulence and virulence factors were restored when φRSM3-encoded orf15, the gene for a putative repressor-like protein, was disrupted. Expression levels of phcA as well as other virulence-related genes in φRSM3-ΔORF15-infected cells were comparable with those in wild-type cells, suggesting that orf15 of φRSM3 may repress phcA and, consequently, result in loss of virulence.