Expression of the gum Operon Directing Xanthan Biosynthesis in Xanthomonas campestris and Its Regulation In Planta

• Published in: Molecular plant-microbe interactions Vol. 14; no. 6; pp. 768 - 774
• Main Authors: Vojnov, Adrian A., Slater, Holly, Daniels, Michael J., Dow, J. Maxwell
• Format: Journal Article
• Language: English
• Published: St Paul, MN APS Press 01.06.2001; The American Phytopathological Society
• Subjects: Bacterial plant pathogens; Bacterial Proteins; Bacterial Proteins - genetics; Bacterial Proteins - physiology; Biological and medical sciences; biosynthesis; black rot; Brassica rapa subsp. rapa; carbohydrate metabolism; Fundamental and applied biological sciences. Psychology; gene expression; Gene Expression Regulation, Bacterial; Gene Expression Regulation, Plant; Genes, Regulator; Genes, Reporter; Genetic Complementation Test; genetics; Glucuronidase; Glucuronidase - genetics; gum gene; gumB gene; leaves; Mutagenesis; Operon; pathogenicity; physiology; Phytopathology. Animal pests. Plant and forest protection; Pigmentation; Pigmentation - genetics; Plant Diseases; Plant Diseases - genetics; Polysaccharides, Bacterial; Polysaccharides, Bacterial - biosynthesis; Polysaccharides, Bacterial - genetics; reporter genes; Signal Transduction; Systematics. Structure, properties and multiplication. Genetics; xanthan gum; Xanthomonas campestris; Xanthomonas campestris - genetics; Xanthomonas campestris - pathogenicity; Pseudomonadales; Operon; Transcription promoter; In situ; Xanthan gum; Host agent relation; Biosynthesis; Metabolic pathway; Gene expression; Brassica rapa var. rapa; Pathogenicity; Xanthomonas campestris; Regulation(control); Vegetable crop; Cruciferae; Dicotyledones; Angiospermae; Bacteria; Pseudomonadaceae; Spermatophyta
• ISSN: 0894-0282; 1943-7706
• DOI: 10.1094/MPMI.2001.14.6.768

The gum gene cluster of Xanthomonas campestris pv. campestris comprises 12 genes whose products are involved in the biosynthesis of the extracellular polysaccharide xanthan. These genes are expressed primarily as an operon from a promoter upstream of the first gene, gumB. Although the regulation of xanthan synthesis in vitro has been well studied, nothing is known of its regulation in planta. A reporter plasmid was constructed in which the promoter region of the gum operon was fused to gusA. In liquid cultures, the expression of the gumgusA reporter was correlated closely with the production of xanthan, although a low basal level of β-glucuronidase activity was seen in the absence of added carbon sources when xanthan production was very low. The expression of the gumgusA fusion also was subject to positive regulation by rpfF, which is responsible for the synthesis of the diffusible signal factor (DSF). The expression of the gumgusA fusion in bacteria recovered from inoculated turnip leaves was maximal at the later phases of growth and was subject to regulation by rpfF. These results provide indirect support for the operation of the DSF regulatory system in bacteria in planta.