Key Laboratory of Integrated Management of Crop Diseases and Pests, Ministry of Education of China, College of Plant Protection, Nanjing Agricultural University, Nanjing, China.
PLoS One. 2012;7(2):e31855. doi: 10.1371/journal.pone.0031855. Epub 2012 Feb 22.
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-N(9)-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.
果糖-1,6-二磷酸醛缩酶（FbaB）是生物糖酵解和糖异生途径中的一种酶。水稻细菌性条斑病菌（Xanthomonas oryzae pv. oryzicola）独特的 fbaB 基因突变体不仅无法利用丙酮酸和苹果酸进行生长，而且当果糖作为唯一碳源时会延迟其生长，同时还降低了胞外多糖（EPS）的产生，并损害了其在水稻中的细菌毒力和生长。有趣的是，fbaB 启动子包含一个不完全的 PIP-box（植物诱导启动子）（TTCGT-N(9)-TTCGT）。fbaB 的表达受关键的 HrpG 和 HrpX 级联的负调控。PIP-box 中的碱基替换改变了级联对 fbaB 的调控。此外，X. oryzae pv. oryzicola RS105 菌株中 fbaB 的表达在植物体内可诱导，而不是在营养丰富的培养基中。除其他 hrp-hrc-hpa 基因外，当 fbaB 缺失时，hrpG 和 hrpX 的转录被抑制，而 hrcC、hrpE 和 hpa3 的转录被增强。hrcC、hrpE 或 hpa3 的突变降低了病原菌获取丙酮酸和苹果酸的能力。此外，在 RΔfbaB 突变体中，通过反式存在 fbaB，可完全恢复细菌毒力和在植物体内的生长以及 EPS 的产生，使其恢复到野生型水平。这是首次报道证明碳水化合物通过未知的调控因子在协调 hrp 基因表达方面起着关键作用。
