Phosphohexose mutase of Xanthomonas oryzae pv. oryzicola is negatively regulated by HrpG and HrpX, and required for the full virulence in rice

Abstract

The genome of Xanthomonas oryzae pv. oryzicola annotates one uncharacterized gene, XOC_3841, only one ORF in this strain is annotated to encode Phosphohexose mutase (XanA), which reversibly converts glucose 1-phosphate to glucose 6-phosphate that implicates in the carbon metabolism pathways. However, it is unclear whether the XanA-coding gene is involved in the full virulence of X. oryzae pv. oryzicola. In this report, we showed that the mutagenesis in unique xanA, led the pathogen effectively to unable to utilize glucose and galactose for growth. The expression of xanA was strongly induced by glucose, sucrose, fructose, mannose or galactose at least 3 times higher than that by non-sugar NY medium. Intriguingly, xanA promoter region contains an imperfect PIP-box (plant-inducible promoter) (TTCGC-N16-TTCGA), and the expression of xanA was inducible in rice suspension cells rather than in a nutrient-rich (NB) medium and negatively regulated by a key hrp regulatory HrpG and HrpX cascade. More importantly, mutation in xanA resulted in impairment of bacterial growth and virulence in planta, and reduced bacterial cell motility and extracellular polysaccharides (EPS) production in media. In addition, the lost properties mentioned above in RΔxanA were completely restored to the wild-type level by the presence of xanA in trans. All these results suggest that xanA is required for EPS production, cell motility and the full virulence of X. oryzae pv. oryzicola.