Genetic Locus Encoding Functions Involved in Biosynthesis and Outer Membrane Localization of Xanthomonadin in Xanthomonas oryzae pv. oryzae

Abstract

Xanthomonadins are membrane-bound, brominated, aryl-polyene pigments specific to the genus Xanthomonas. We have characterized a genetic locus (pig) from Xanthomonas oryzae pv. oryzae which contains four open reading frames (ORFs) that are essential for xanthomonadin production. Three of these ORFs are homologous to acyl carrier proteins, dehydratases, and acyl transferases, suggesting a type II polyketide synthase pathway for xanthomonadin biosynthesis. The fourth ORF has no homologue in the database. For the first time, we report that a putative cytoplasmic membrane protein encoded in the pig locus is required for outer membrane localization of xanthomonadin in X. oryzae pv. oryzae. We also report the identification of a novel 145-bp palindromic Xanthomonas repetitive intergenic consensus element that is present in two places in the pig locus. We estimate that more than 100 copies of this element might be present in the genome of X. oryzae pv. oryzae and other xanthomonads.Members of the genus Xanthomonas cause diseases in a wide range of host plants (25). Many of them can also survive and multiply on plant leaf surfaces as epiphytes without affecting the host (15,44). A characteristic feature of most xanthomonads is the production of yellow, membrane-bound (46), halogenated, aryl-polyene pigments (2, 3) called xanthomonadins, which serve as useful chemotaxonomic (45) and diagnostic markers (41). Xanthomonadin is not essential for in planta growth of bacterial cells (13,35,48). However, it is being established progressively that xanthomonadin protects bacteria against photooxidative damage. Pigment-deficient mutants of Xanthomonas juglandis (20), Xanthomonas oryzae pv. oryzae (37), and Xanthomonas campestris pv. campestris (33) are more susceptible to photooxidative damage than are wild-type strains. In vitro, xanthomonadin protects membrane lipids in egg-phosphatidylcholine liposomes against peroxidation (37). A transposon-induced xanthomonadin-deficient mutant of X. campestris pv. campestris has been recently shown to be 1,000-fold reduced for epiphytic survival in conditions of high light intensity (33). These observations suggest that xanthomonadin might aid the survival of xanthomonads on plant leaf surfaces by providing protection against photooxidative damage. In spite of their apparent importance, very little is known about the biosynthesis and mechanism of action of xanthomonadins.An 18.6-kb genomic region from X. campestris pv. campestris that contains seven transcriptional units (pig genes) required for xanthomonadin production has been isolated (34, 35). One of the transcriptional units, pigB, is involved in biosynthesis of a diffusible factor that affects the production of xanthomonadin as well as extracellular polysaccharide (34). The unavailability of nucleotide sequences for these transcriptional units, however, limits further insight into the mechanism of xanthomonadin biosynthesis. X. oryzae pv. oryzae mutants that are defective in shikimate dehydrogenase activity have been shown to be deficie...

Genomic Insights into the Evolutionary Origin of Xanthomonas axonopodis pv. citri and Its Ecological Relatives

“…The gene cluster responsible for the xanthomonadin pigment production has already been identified in X. campestris pv. campestris (40) and Xoo (41). A similar gene cluster was found in the genomes of pathovars Xac, Xap, and Xvt, while in Xmi, we were not able to find the complete cluster.…”

“…But Xvt was found to have a frameshift mutation because of a deletion of four nucleotides in the gene coding for phosphotransferase/dehydratase (already reported as necessary for pigment production [41]) at position 352 which has resulted in the formation of a truncated protein. The length of the protein in Xac is 143 amino acids, but in the case of Xvt the protein is terminated earlier, at 122 amino acids, because of the deletion of four nucleotides (bp 352 to 355).…”

Identification of bacterial leaf blight resistance genes in wild rice of eastern India

“…The amplified PCR products with a 100-bp DNA marker ladder (MBI, Fermentas) were sizefractioned by electrophoresis in 2.5% agarose gel prepared in TAE buffer and visualized by staining with ethidium bromide (0.5 µg/mL) in a gel documentation system (BioRad, USA). (Goel et al, 2002). The results of phenotypic screening are presented in Table 2.…”

Granadaene: Proposed Structure of the Group B Streptococcus Polyenic Pigment

“…Although polyenic pigments are found in fungi (2), in bacteria they have been reported only for Xanthomonas (4). The GBS pigment is considered a virulence factor based on the assumption that it is a carotene and on the fact that it is always associated with the hemolysin/cytolysin (6, 7).…”