Cell–cell signalling promotes ferric iron uptake in Xanthomonas oryzae pv. oryzicola that contribute to its virulence and growth inside rice

Abstract

SummaryCell-cell communication mediated by diffusible signal factor (DSF) plays an important role in virulence of several Xanthomonas group of plant pathogens. In the bacterial pathogen of rice, Xanthomonas oryzae pv. oryzicola, DSF is required for virulence and in planta growth. In order to understand the role of DSF in promoting in planta growth and virulence, we have characterized the DSF deficient mutant of X. oryzae pv. oryzicola. Mutant analysis by expression analysis, radiolabelled iron uptake studies and growth under low-iron conditions indicated that DSF positively regulates ferric iron uptake. Further, the DSF deficient mutant of X. oryzae pv. oryzicola exhibited a reduced capacity to use ferric form of iron for growth under low-iron conditions. Exogenous iron supplementation in the rice leaves rescued the in planta growth deficiency of the DSF deficient mutant. These data suggest that DSF promotes in planta growth of X. oryzae pv. oryzicola by positively regulating functions involved in ferric iron uptake which is important for its virulence. Our results also indicate that requirement of iron uptake strategies to utilize either Fe 3+ or Fe 2+ form of iron for colonization may vary substantially among closely related members of the Xanthomonas group of plant pathogens.

Using Ecology, Physiology, and Genomics to Understand Host Specificity inXanthomonas

“…In X. oryzae species, xylem-inhabiting Xoo and mesophyll-colonizing Xoc share the xsu-xss gene cluster that is involved in the biosynthesis and the capture of ferric iron (102,108). Both pathovars, Xoo and Xoc, also share the feoABC system involved in the uptake of free ferrous iron (102,108). For Xoo, a feoB mutant is impaired in virulence, whereas xss mutants are not.…”

“…However, the uptake of iron is tightly controlled because Fe 2+ catalyzes the Fenton reaction, generating highly reactive hydroxyl radicals that can oxidize macromolecules (68). In X. oryzae species, xylem-inhabiting Xoo and mesophyll-colonizing Xoc share the xsu-xss gene cluster that is involved in the biosynthesis and the capture of ferric iron (102,108). Both pathovars, Xoo and Xoc, also share the feoABC system involved in the uptake of free ferrous iron (102,108).…”

Co-regulation of Iron Metabolism and Virulence Associated Functions by Iron and XibR, a Novel Iron Binding Transcription Factor, in the Plant Pathogen Xanthomonas

“…To understand the role of xibR in iron uptake and storage, we performed in vitro 55 Fe 3 + , 55 Fe 2+ and 55 Fe 3 + -vibrioferrin complex uptake assays with wild-type Xcc 8004, the ΔxibR mutant, ΔxibR mutant harboring the plasmid-borne wild-type xibR allele ( ΔxibR /pSSP30), and the ΔxibR harboring the plasmid-borne point mutant D55AXibR allele ( ΔxibR /pSSP39) as described previously [13,28,29] with few modifications (see Materials and Methods). The total amount of 55 Fe 3+ incorporated into the Δ xibR mutant or Δ xibR /pSSP39 was significantly less than that incorporated into the wild-type Xcc 8004 and the Δ xibR /pSSP30 over the 10 min time-course of the experiment (Fig 4A).…”

“…We next performed streptonigrin sensitivity assay, which depends on the intracellular iron levels, to assess intracellular iron content in different strains of Xcc [13,32]. Streptonigrin sensitivity assay indicated that the wild-type Xcc 8004 and Δ xibR /pSSP30 strains were hypersensitive to streptonigrin compared to the Δ xibR and Δ xibR /pSSP39 (Fig 4E; S9D Fig), indicative of low intracellular iron level in the Δ xibR mutant.…”

“…Xanthomonads encodes an xss ( X anthomonas s iderophore s ynthesis) operon which is required for the production of siderophore vibrioferrin under iron-restricted conditions, and iron metabolism plays a critical role in their virulence [12–14]. These phytopathogen use cell-cell signaling mediated by diffusible quorum sensing signal molecule to regulate the expression of iron uptake and metabolism functions contributing to virulence and growth within host [13,15]. In Xanthomonas campestris pv.…”