Open AccessSynergistic interaction between the type III secretion system of the endophytic bacterium Pantoea agglomerans DAPP‐PG 734 and the virulence of the causal agent of olive knot Pseudomonas savastanoi pv. savastanoi DAPP‐PG 722
Author(s) -
Moretti Chiaraluce,
Rezzonico Fabio,
Orfei Benedetta,
Cortese Chiara,
MorenoPérez Alba,
den Burg Harrold A.,
Onofri Andrea,
Firrao Giuseppe,
Ramos Cayo,
Smits Theo H. M.,
Buonaurio Roberto
Publication year - 2021
Publication title -
molecular plant pathology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.945
H-Index - 103
eISSN - 1364-3703
pISSN - 1464-6722
DOI - 10.1111/mpp.13105
Subject(s) - biology , pantoea agglomerans , microbiology and biotechnology , type three secretion system , virulence , mutant , bacteria , wild type , enterobacteriaceae , escherichia coli , gene , genetics
The endophytic bacterium Pantoea agglomerans DAPP‐PG 734 was previously isolated from olive knots caused by infection with Pseudomonas savastanoi pv. savastanoi DAPP‐PG 722. Whole‐genome analysis of this P. agglomerans strain revealed the presence of a Hypersensitive response and pathogenicity ( Hrp ) type III secretion system (T3SS). To assess the role of the P. agglomerans T3SS in the interaction with P . savastanoi pv. savastanoi , we generated independent knockout mutants in three Hrp genes of the P. agglomerans DAPP‐PG 734 T3SS ( hrpJ , hrpN , and hrpY ). In contrast to the wildtype control, all three mutants failed to cause a hypersensitive response when infiltrated in tobacco leaves, suggesting that P. agglomerans T3SS is functional and injects effector proteins in plant cells. In contrast to P . savastanoi pv. savastanoi DAPP‐PG 722, the wildtype strain P . agglomerans DAPP‐PG 734 and its Hrp T3SS mutants did not cause olive knot disease in 1‐year‐old olive plants. Coinoculation of P . savastanoi pv. savastanoi with P. agglomerans wildtype strains did not significantly change the knot size, while the DAPP‐PG 734 hrpY mutant induced a significant decrease in knot size, which could be complemented by providing hrpY on a plasmid. By epifluorescence microscopy and confocal laser scanning microscopy, we found that the localization patterns in knots were nonoverlapping for P . savastanoi pv. savastanoi and P. agglomerans when coinoculated. Our results suggest that suppression of olive plant defences mediated by the Hrp T3SS of P. agglomerans DAPP‐PG 734 positively impacts the virulence of P . savastanoi pv. savastanoi DAPP‐PG 722.