Ralstonia solanacearum RSc0411 (lptC) is a determinant for full virulence and has a strain-specific novel function in the T3SS activity

Previously, we have identified an avirulent Ralstonia solanacearum mutant carrying a transposon insertion in RSc0411, a gene homologous to the Escherichia coli LPS-transporting protein LptC. However, how the disruption of RSc0411 affects the bacterium-plant interactions and leads to decreased pathogenicity was not known. Here we show that the disruption of RSc0411 leads to pleiotropic defects, including reducing bacterial motility, biofilm formation, root attachment, rough-form LPS production and virulence in tomato and increasing membrane permeability. Disruption of the orthologous RSc0411 present in other R. solanacearum strains proves that most of these functions are conserved in the species. In contrast, trans-complementation analyses show that only RSc0411 orthologues from closely related bacteria can rescue the defects of the disruption mutant. These results enable us to propose a function for RSc0411, and for the clustered genes, in LPS biogenesis, and for the first time, to our knowledge, also a role of a gene from the DUF1239 gene family in bacterial pathogenicity. In addition and notably, the RSc0411 mutant displays a strain-specific phenotype for hypersensitive response (HR), in which the RSc0411 disruption impairs the HR caused by strain Pss190 but not that by strain Pss1308. Consistent with this strain-specific defect, the mutation clearly affects expression of the type III secretion system (T3SS) in Pss190 but not in other strains, suggesting that the HR-deficient phenotype of the RSc0411 mutant in Pss190 is due to impairment of the T3SS and thus RSc0411 has a strain-specific role in the T3SS activity of R. solanacearum.