Enhanced colonization and pathogenicity of Erwinia amylovora strains transformed with the near‐ubiquitous pEA29 plasmid on pear and apple

Abstract

Three plasmid-free strains of Erwinia amylovora, the causal agent of fire blight disease of pome trees, one from Iran, one from Egypt and one from Spain, were transformed with the near-ubiquitous nonconjugative pEA29 plasmid from a wildtype strain and characterized. The plasmid-deficient strains were levan-and slime-positive, motile, chemotaxis-positive, induced HR on Nicotiana tabacum var. xanthi but produced several-fold less amylovoran and were weakly pathogenic on pear slices and apple seedlings compared to plasmid-bearing wild-type strains. When inoculated onto wounded young apple (cv. Royal Gala) leaves, the plasmid-free strains labelled with green fluorescent protein gene (gfp) were mainly restricted to the inoculation site at the leaf tips, in contrast to the plasmid-carrying wild-type strains that moved into the midrib xylem vessel and colonized the adjacent parenchyma cells. Upon introduction of the transposon-labelled pEA29 plasmid, amylovoran production, degree of oozing and tissue necrosis on pear slices were significantly elevated in all three strains, whilst the levels of levan and levansucrase declined. Only the strains from Iran and Egypt gained the ability to invade and colonize the young apple leaves following the introduction of pEA29. It is concluded that acquisition of the nonconjugative near-ubiquitous plasmid may not necessarily confer increasing pathogenicity in all bacterial strains.

Erwinia amylovora Novel Plasmid pEI70: Complete Sequence, Biogeography, and Role in Aggressiveness in the Fire Blight Phytopathogen

“…In contrast, no significant effect of the introduction of pEA29 was observed on the incidence of infection in two strains that naturally only harbor plasmid pEI70 (i.e., IVIA 1596 and IVIA 1614-2a) ( Table 4 ). In other studies, introduction of pEA29 in strains without this plasmid provided different levels of aggressiveness, depending on the strain studied [49] . These results suggest the possible influence of other factors such as genomic background, host interactions and environmental conditions on the variability in aggressiveness that remains unexplained.…”

Pathogenicity and infection strategies of the fire blight pathogen Erwinia amylovora in Rosaceae: State of the art

“…Besides the production of the siderophore desferrioxamine for the acquisition of iron molecules from the host tissue (Dellagi et al, 1998;Expert, 1999; and the presence of other virulence factors such as metalloproteases (Zhang et al, 1999), the presence of plasmids (Llop et al, 2011(Llop et al, , 2012McGhee & Jones, 2000;Mohammadi, 2010), two-component signal transduction systems Zhao et al, 2009) and histone-like proteins (Hildebrand et al, 2006) are also important factors in pathogenesis. However, probably the most essential reasons for differences in virulence between different strains of E. amylovora are due to a variation in synthesis of exopolysaccharides and the mechanism of the type III secretion system (T3SS) and associated proteins.…”

Function and Application of the CRISPR-Cas System in the Plant PathogenErwinia amylovora

“…Each transformation consisted of 400 µL of bacterial suspension and 50 ng of plasmid DNA. Electroporation occurred in 2 mm electroporation cuvettes using a Bio-Rad Gene Pulser Electroporator (Bio-Rad Laboratories, Hercules, CA, USA) with the following settings: 800 Ω, 25 µF, and 2.5 kV for 4s ( 38 ). Transformants were immediately diluted with 600 µL of SOC media ( 39 ) and incubated at 27°C for 1 h. A 100 µL aliquot of the transformed bacteria was plated on NAS amended with ampicillin, kanamycin or both ampicillin and kanamycin.…”