An Inner Membrane Protein (Imp) of Xanthomonas oryzae pv. oryzicola Functions in Carbon Acquisition, EPS Production, Bacterial Motility and Virulence in Rice

Abstract

Xanthomonas oryzae pv. oryzicola (Xoc) causes bacterial leaf streak, a devastating disease in rice-growing regions worldwide. A Tn5-insertion mutant in Xoc_3248, encoding an inner membrane protein (Imp), showed reduced virulence in rice. To explore the potential function of this gene in virulence, a deletion mutant RΔimp was constructed in the wild-type RS105. The RΔimp mutant was significantly impaired for bacterial virulence and growth in planta. The mutation in imp made the pathogen insufficiently utilize glucose, fructose, mannose or pyruvate as a sole carbon source, leading to less extracellular polysaccharide (EPS) production and reduced motility. The deficiencies noted for the mutant were restored to wild-type levels when imp was introduced in trans. Transcription of imp was significantly declined when hrpG and hrpX was mutated and the expression of hrpG and hrpX was also significantly declined when imp was deleted. Cell sublocalization in planta showed Imp membrane-binding feature. These results suggest that Imp is a virulence factor with roles in the catabolism of sugars, EPS production, and bacterial motility.

Keywords

• Xanthomonas oryzae pv. oryzicola
• inner membrane protein
• extracellular polysaccharide
• motility
• virulence