Virulence Factors in the Phytopathogen–Host Interactions: An Overview

Abstract

Phytopathogens are responsible for great losses in agriculture, once they are able to subvert or elude the host defense mechanisms through virulence factors secretion for their dissemination. Herein, it is reviewed phytotoxins that act as virulence factors and are produced by bacterial phytopathogens (Candidatus Liberibacter spp., Erwinia amylovora, Pseudomonas syringae pvs and Xanthomonas spp.) and fungi (Alternaria alternata, Botrytis cinerea, Cochliobolus spp., Fusarium spp., Magnaporthe spp., and Penicillium spp.), which were selected in accordance to their worldwide importance due to the biochemical and economical aspects. In the current review, it is sought to understand the role of virulence factors in the pathogen–host interactions that result in plant diseases.

A light life together: photosensing in the plant microbiota

“…Not withstanding the major role played by FphA in light regulation, the key enzyme for BV production, heme oxygenase, has not yet been found in this fungus [123]. A similar light regulation as in E. nidulans has been described for Alternaria alternata, a food contaminant and plant pathogen causing leaf spots, rots, and blights on many plant parts, producing diverse health-endangering mycotoxins, e.g., alteraniol and altertoxins [124,125]. BL inhibits asexual sporulation, while RL reverses this effect underscoring interplay between different photoreceptors with LreA taking a prominent role; deletion mutants in FphA and LreA showed a reduced sporulation in the dark, suggesting also light-independent roles for these photoreceptors: in the fphA mutant conidiation was reduced by 86% in the dark with respect to the WT strain [126].…”

“…Importantly, BL and GL stimulate production of the mutagenic toxin alternariol, an effect due to the LOV protein LreA [126]. Until now it was not possible to detect any light effect on the virulence of A. alternata, an aspect particularly relevant, because Alternaria species cause at least 20% of crop losses of all fungal-mediated diseases, as it infects a broad variety of agricultural plants [125].…”

Evolutionary epidemiology consequences of trait-dependent control of heterogeneous parasites

“…Several plant bacteria are united by the use of phytotoxins as virulence factors 51 : for instance, Candidatus Liberibacter spp. (affecting different species of citrus), Erwinia amylovora (the Fire Blight infesting apple and pear orchards), Xanthomonas spp.…”

Function of pH‐dependent transcription factor PacC in regulating development, pathogenicity, and mycotoxin biosynthesis of phytopathogenic fungi

“…In P. expansum, pacC-RNAi mutants exhibited a 45% reduction in pathogenicity in apple fruit, but did not demonstrate significant reduction in growth, indicating that PacC may directly contribute to pathogenicity [37]. Small molecules, such as organic acids and phytotoxins, are also considered key virulence factors [41,42]. P. expansum and A. carbonarius acidify the fruit tissue of infection sites by secreting significant amounts of organic acids to facilitate their infection, such as gluconic acid and citric acid [37,43,44].…”