Modulation of Defense Responses of Malus spp. During Compatible and Incompatible Interactions with Erwinia amylovora

Abstract

Erwinia amylovora is the causal agent of fire blight, a disease affecting members of subfamily Maloideae. In order to analyze mechanisms leading to compatible or incompatible interactions, early plant molecular events were investigated in two genotypes of Malus with contrasting susceptibility to fire blight, after confrontation with either E. amylovora or the incompatible tobacco pathogen Pseudomonas syringae pv. tabaci. Many defense mechanisms, including generation of an oxidative burst and accumulation of pathogenesis-related proteins, were elicited in both resistant and susceptible genotypes by the two pathogens at similar rates and according to an equivalent time course. This elicitation was linked with the functional hypersensitive reaction and pathogenicity (hrp) cluster of E. amylovora, because an hrp secretion mutant did not induce such responses. However, a delayed induction of several genes of various branch pathways of the phenylpropanoid metabolism was recorded in tissues of the susceptible genotype challenged with the wild-type strain of E. amylovora, whereas these genes were quickly induced in every other plant-bacteria interaction, including interactions with the hrp secretion mutant. This suggests the existence of hrp-independent elicitors of defense in the fire blight pathogen as well as hrp-dependant mechanisms of suppression of these nonspecific inductions.

Phenolic profiles in apple leaves and the efficacy of selected phenols against fire blight (Erwinia amylovora)

“…Speculatively, the participation of SA and JA in plant HR during the consecutive stages of invasion by E. amylovora may suggest that this pathogen can behave as hemi-necrotroph or necrotroph, as recently reported by Sobiczewski et al (2016). In the various cases of pome fruit trees interaction with pathogens an increase or decrease of the levels of phenolic compounds is found (Venisse et al 2002;Gosch et al 2010). Taking into consideration the role of oxidative stress in HR and the antioxidant properties of phenolics, it might be suggested that by influencing the redox state they are able to modulate the course of HR (Glazebrook 2005).…”

“…The potential of the phenylpropanoid-flavonoid pathway to produce different end products is depended on the activities of enzymes such as reductases, oxygenases, ligases or transferases (Venisse et al 2002;Gosch et al 2010). The biosynthesis of phenolics is organ-and species-specific, proceeds in different rate and the spectrum of the compounds varies during the developmental stages (Treutter 2001).…”

“…The biosynthesis of phenolics is organ-and species-specific, proceeds in different rate and the spectrum of the compounds varies during the developmental stages (Treutter 2001). In response to pathogen infection, the synthesis of defense-related phenolics such as flavonoids, phenolamines, flavonoid phytoalexins, lignin and salicylic acid (SA) is enhanced (Treutter 2001;Venisse et al 2002;Fischer et al 2007). Jensen et al (2012) suggested that the phenylpropanoid pathway mobilization and activity might be one of the hallmarks of fire blight resistance.…”

“…Jensen et al (2012) suggested that the phenylpropanoid pathway mobilization and activity might be one of the hallmarks of fire blight resistance. However, it should be taken into account that although the stimulation of this pathway is a part of plant resistance response, the processes are dependent also on pathogen activity; E. amylovora belongs to the pathogens which in order to overcome plant defense can delay the expression of phenylpropanoid genes (Venisse et al 2002).…”

Identification of a major QTL together with several minor additive or epistatic QTLs for resistance to fire blight in apple in two related progenies

“…Candidate genes involved in the transduction cascade leading from pathogen recognition to the resistance phenotype or in the defence response should also be mapped to look for genetic co-localizations. Such candidates have already been identified by Venisse et al (2002), and the genetic mapping of some of these has been initiated (data not shown). The characterization of the F7 QTL could also be achieved by looking for genes expressed differentially between individuals carrying either the favourable or the unfavourable allele at this QTL by means of a differential display approach (for example, cDNA-AFLP performed on genotype bulks).…”