Fructose-Bisphophate Aldolase Exhibits Functional Roles between Carbon Metabolism and the hrp System in Rice Pathogen Xanthomonas oryzae pv. oryzicola

Abstract

Fructose-bisphophate aldolase (FbaB), is an enzyme in glycolysis and gluconeogenesis in living organisms. The mutagenesis in a unique fbaB gene of Xanthomonas oryzae pv. oryzicola, the causal agent of rice bacterial leaf streak, led the pathogen not only unable to use pyruvate and malate for growth and delayed its growth when fructose was used as the sole carbon source, but also reduced extracellular polysaccharide (EPS) production and impaired bacterial virulence and growth in rice. Intriguingly, the fbaB promoter contains an imperfect PIP-box (plant-inducible promoter) (TTCGT-N9-TTCGT). The expression of fbaB was negatively regulated by a key hrp regulatory HrpG and HrpX cascade. Base substitution in the PIP-box altered the regulation of fbaB with the cascade. Furthermore, the expression of fbaB in X. oryzae pv. oryzicola RS105 strain was inducible in planta rather than in a nutrient-rich medium. Except other hrp-hrc-hpa genes, the expression of hrpG and hrpX was repressed and the transcripts of hrcC, hrpE and hpa3 were enhanced when fbaB was deleted. The mutation in hrcC, hrpE or hpa3 reduced the ability of the pathogen to acquire pyruvate and malate. In addition, bacterial virulence and growth in planta and EPS production in RΔfbaB mutant were completely restored to the wild-type level by the presence of fbaB in trans. This is the first report to demonstrate that carbohydrates, assimilated by X. oryzae pv. oryzicola, play critical roles in coordinating hrp gene expression through a yet unknown regulator.

GamR, the LysR-Type Galactose Metabolism Regulator, Regulates hrp Gene Expression via Transcriptional Activation of Two Key hrp Regulators, HrpG and HrpX, in Xanthomonas oryzae pv. oryzae

“…For X. oryzae pv. oryzicola, Guo et al (39) reported that fructose-bisphosphate aldolase, which is essential for glycolysis and gluconeogenesis to reversibly convert fructose-1,6-bisphosphate to dihydroxyacetone phosphate and glyceraldehyde 3-phosphate, is involved in positive regulation of two key hrp regulator genes, hrpG and hrpX. In the present study, we found that a LysRtype transcriptional regulator that regulates galactose metabolism also regulates hrpG and hrpX by binding directly to their common upstream region.…”

Ketoglutarate Transport Protein KgtP Is Secreted through the Type III Secretion System and Contributes to Virulence in Xanthomonas oryzae pv. oryzae

“…oryzae PXO99 A strains were grown at 28°C in NB (0.1% yeast extract, 0.3% beef extract, 0.5% polypeptone, and 1% sucrose), NA (NB with 15 g/liter agar), NAN (NA without sucrose), NAS (NA with 10% sucrose), and NY (NB without beef extract and sucrose). In some experiments, strains were grown in MMX minimal medium [0.5% glucose, 0.2% (NH 4 ) 2 SO 4 , 0.1% trisodium citrate dihydrate, 0.4% K 2 HPO 4 , 0.6% KH 2 PO 4 , 0.02% MgSO 4 · 7H 2 O], NCM (noncarbohydrate) medium (15,54), or XOM3 medium (65) or with rice suspension cells (65). Antibiotics were added at the following concentrations (g/ml) when required: kanamycin (Km), 25; rifampin (Rif), 50; ampicillin (Ap), 100; spectinomycin (Sp), 50; and streptomycin (Sm), 50.…”

“…Assays for the hypersensitive response (HR) and pathogenicity were performed as described previously (15,70). Briefly, Xanthomonas cells were grown in NB broth with appropriate antibiotics at 28°C and 200 rpm for 16 h, when cells approached the exponential phase of growth.…”

Metabolite profiles of rice cultivars containing bacterial blight-resistant genes are distinctive from susceptible rice

“…carbohydrates play critical roles in rice pathogen X. oryzae pv. oryzicola [41]. Furthermore, in our study, the common difference in physical characteristics and metabolic profile variation of both BB resistant rice seeds may be induced by the defense response owing to foreign gene expression.…”