Extragenic Suppression of Elongation Factor P Gene Mutant Phenotypes in Erwinia amylovora.

Elongation factor P (EF-P) facilitates the translation of certain peptide motifs, including those with multiple proline residues. EF-P must be posttranslationally modified for full functionality; in enterobacteria, this is accomplished by two enzymes, namely, EpmA and EpmB, which catalyze the β-lysylation of EF-P at a conserved lysine position. Mutations to or its modifying enzymes produce pleiotropic phenotypes, including decreases in virulence, swimming motility, and extracellular polysaccharide production, as well as proteomic perturbations. Here, we generated targeted deletion mutants of the , , and genes in the Gram-negative bacterium , which causes fire blight, an economically important disease of apples and pears. As expected, the Δ, Δ, and Δ mutants were all defective in virulence on apples, and all three mutants were complemented in with plasmids bearing wild-type copies of the corresponding genes. By analyzing spontaneous suppressor mutants, we found that mutations in the gene partially or completely suppressed the colony size, extracellular polysaccharide production, and virulence phenotypes in apple fruits and apple tree shoots but not the swimming motility phenotypes of the Δ, Δ, and Δ mutants. The deletion of alone did not produce any alterations in any characteristics measured, indicating that the HrpA3 protein is not essential for any of the processes examined. The gene encodes a putative DEAH-box ATP-dependent RNA helicase. These results suggest that the loss of the HrpA3 protein at least partially compensates for the lack of the EF-P protein or β-lysylated EF-P. Fire blight disease has relatively few management options, with antibiotic application at bloom time being chief among them. As modification to elongation factor P (EF-P) is vital to virulence in several species, both EF-P and its modifying enzymes make attractive targets for novel antibiotics. However, it will be useful to understand how bacteria might overcome the hindrance of EF-P function so that we may be better prepared to anticipate bacterial adaptation to such antibiotics. The present study indicates that the mutation of could provide a partial offset for the loss of EF-P activity. In addition, little is known about EF-P functional interactions or the HrpA3 predicted RNA helicase, and our genetic approach allowed us to discern a novel gene associated with EF-P function.