Department of Plant Pathology & Environmental Microbiology, The Pennsylvania State University, University Park, PA 16802, USA.
Mol Plant Pathol. 2013 Oct;14(8):838-43. doi: 10.1111/mpp.12045. Epub 2013 May 30.
RpoN is a σ(54) factor regulating essential virulence gene expression in several plant pathogenic bacteria, including Pseudomonas syringae and Pectobacterium carotovorum. In this study, we found that mutation of rpoN in the fire blight pathogen Erwinia amylovora caused a nonpathogenic phenotype. The E. amylovora rpoN Tn5 transposon mutant rpoN1250::Tn5 did not cause fire blight disease symptoms on shoots of mature apple trees. In detached immature apple fruits, the rpoN1250::Tn5 mutant failed to cause fire blight disease symptoms and grew to population levels 12 orders of magnitude lower than the wild-type. In addition, the rpoN1250::Tn5 mutant failed to elicit a hypersensitive response when infiltrated into nonhost tobacco plant leaves, and rpoN1250::Tn5 cells failed to express HrpN protein when grown in hrp (hypersensitive response and pathogenicity)-inducing liquid medium. A plasmid-borne copy of the wild-type rpoN gene complemented all the rpoN1250::Tn5 mutant phenotypes tested. The rpoN1250::Tn5 mutant was prototrophic on minimal solid and liquid media, indicating that the rpoN1250::Tn5 nonpathogenic phenotype was not caused by a defect in basic metabolism or growth. This study provides clear genetic evidence that rpoN is an essential virulence gene of E. amylovora, suggesting that rpoN has the same function in E. amylovora as in P. syringae and Pe. carotovorum.
RpoN 是一种 σ(54) 因子，可调节几种植物病原菌（包括丁香假单胞菌和菊欧文氏菌）中必需的毒力基因表达。在本研究中，我们发现，火疫病病原菌韧皮部杆菌 rpoN 的突变导致了非致病性表型。E. amylovora rpoN Tn5 转座子突变体 rpoN1250::Tn5 不会在成熟苹果树的枝条上引起火疫病症状。在分离的未成熟苹果果实中，rpoN1250::Tn5 突变体未能引起火疫病症状，其种群水平比野生型低 12 个数量级。此外，rpoN1250::Tn5 突变体在非宿主烟草植物叶片中不能引发过敏反应，当在 hrp（过敏反应和致病性）诱导液体培养基中生长时，rpoN1250::Tn5 细胞不能表达 HrpN 蛋白。携带野生型 rpoN 基因的质粒拷贝完全补充了所有测试的 rpoN1250::Tn5 突变体表型。rpoN1250::Tn5 突变体在最小固体和液体培养基上是原养型的，这表明 rpoN1250::Tn5 非致病性表型不是由于基本代谢或生长缺陷引起的。本研究提供了明确的遗传证据，表明 rpoN 是 E. amylovora 的必需毒力基因，这表明 rpoN 在 E. amylovora 中的功能与 P. syringae 和 Pe. carotovorum 中的相同。
