Zhang J H, Quigley N B, Gross D C
Department of Plant Pathology, Washington State University, Pullman 99164-6430, USA.
Appl Environ Microbiol. 1997 Jul;63(7):2771-8. doi: 10.1128/aem.63.7.2771-2778.1997.
Syringomycin is a lipodepsinonapeptide phytotoxin synthesized by Pseudomonas syringae pv. syringae on multienzymatic peptide synthetases. Sequence analysis of the interval between the syrB and syrD genes of P. syringae pv. syringae strain B301D revealed a 1,059-bp open reading frame (ORF), designated syrP. The predicted product of this ORF was a 39.6-kDa protein consisting of 353 amino acid residues. Searches of protein sequence databases demonstrated that SyrP was most similar to histidine kinases such as the CheA regulatory protein of Escherichia coli. The predicted SyrP sequence was aligned with the N terminus of CheA, a region corresponding to the phosphotransfer and acceptor domains of CheA. The SyrP region that aligns with the phosphotransfer domain of CheA contained a His at position 101 which is flanked by a weak consensus sequence of the unorthodox sensory kinase subfamily of two-component regulatory systems. Strain B301D-31, obtained by site-directed insertional mutagenesis of the syrP gene, exhibited an unusual pleiotropic phenotype including a failure to produce syringomycin in liquid media in contrast to production of elevated levels of the toxin on agar media. The syrP mutant was relieved of the suppression of toxin production that accompanies inorganic phosphate concentrations of > 1 mM on agar media. Nevertheless, the syrP mutant was substantially less virulent than the wild-type strain in pathogenicity assays in cherry fruits. These results suggest that the syrP gene encodes a regulatory protein that participates in a phosphorylation cascade controlling syringomycin production and virulence in P. syringae pv. syringae.
丁香霉素是一种脂缩酚九肽植物毒素，由丁香假单胞菌丁香致病变种在多酶肽合成酶上合成。对丁香假单胞菌丁香致病变种B301D菌株的syrB和syrD基因之间的间隔进行序列分析，发现了一个1059 bp的开放阅读框（ORF），命名为syrP。该ORF的预测产物是一种由353个氨基酸残基组成的39.6 kDa蛋白质。蛋白质序列数据库搜索表明，SyrP与组氨酸激酶最为相似，如大肠杆菌的CheA调节蛋白。将预测的SyrP序列与CheA的N端进行比对，该区域对应于CheA的磷酸转移和受体结构域。与CheA的磷酸转移结构域比对的SyrP区域在第101位含有一个组氨酸，其两侧是双组分调节系统非正统感觉激酶亚家族的弱共有序列。通过对syrP基因进行定点插入诱变获得的菌株B301D-31表现出一种不寻常的多效性表型，包括在液体培养基中不能产生丁香霉素，而在琼脂培养基上毒素产量升高。syrP突变体在琼脂培养基上解除了无机磷酸盐浓度>1 mM时伴随的毒素产生抑制作用。然而，在樱桃果实致病性试验中syrP突变体比野生型菌株的毒力显著降低。这些结果表明，syrP基因编码一种调节蛋白，参与控制丁香假单胞菌丁香致病变种中丁香霉素产生和毒力的磷酸化级联反应。
