The fire blight pathogen Erwinia amylovora requires the rpoN gene for pathogenicity in apple

Abstract

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.

Mutation of the Erwinia amylovora argD Gene Causes Arginine Auxotrophy, Nonpathogenicity in Apples, and Reduced Virulence in Pears

“…2). Supplementation of M9 minimal medium with thiamine and nicotinic acid allows wild-type E. amylovora bacteria to grow by several orders of magnitude; in contrast, wild-type E. amylovora does not grow by even a single order of magnitude in M9 minimal medium in the absence of thiamine and nicotinic acid (23). Therefore, the use of M9TN medium allows for easier identification of auxotrophic E. amylovora mutants.…”

“…Novel E. amylovora genes contributing to virulence and pathogenicity continue to be discovered to this day, including recent examples like waaL, rpoN, rcs, luxS, and hns (21)(22)(23)(24)(25)(26). These genetic studies provide a better understanding of the pathogen and have the potential to provide new methods to manage the disease.…”

Malus Hosts–Erwinia amylovora Interactions: Strain Pathogenicity and Resistance Mechanisms

“…Knockout of genes of the pathogenicity island of different E . amylovora strains and other E a mutations, which have led to the discovery of more virulence factors (Ramos et al., 2013, 2015; Klee et al., 2018), will improve our understanding of the pathogenic process.…”

rpoN1, but not rpoN2, is required for twitching motility, natural competence, growth on nitrate, and virulence of Ralstonia solanacearum

“…Evidence of rpoN involvement in bacterial pathogenesis and virulence, mainly through the control of flagellar motility, is also documented (Kazmierczak et al, 2005 ). However, rpoN does not share a common role in plant pathogens: in Pseudomonas syringae, Pectobacterium carotovorum , and Erwinia amylovora rpoN is required for virulence and is involved in the regulation of the type III secretion system (Hendrickson et al, 2000a , b ; Chatterjee et al, 2002 ; Ramos et al, 2013 ) but in Xanthomonas campestris pv. vesicatoria , disruption of rpoN has no impact on virulence (Horns and Bonas, 1996 ).…”