The Role of Pathogen-Secreted Proteins in Fungal Vascular Wilt Diseases

Abstract

A limited number of fungi can cause wilting disease in plants through colonization of the vascular system, the most well-known being Verticillium dahliae and Fusarium oxysporum. Like all pathogenic microorganisms, vascular wilt fungi secrete proteins during host colonization. Whole-genome sequencing and proteomics screens have identified many of these proteins, including small, usually cysteine-rich proteins, necrosis-inducing proteins and enzymes. Gene deletion experiments have provided evidence that some of these proteins are required for pathogenicity, while the role of other secreted proteins remains enigmatic. On the other hand, the plant immune system can recognize some secreted proteins or their actions, resulting in disease resistance. We give an overview of proteins currently known to be secreted by vascular wilt fungi and discuss their role in pathogenicity and plant immunity.

Transcriptome analysis of the fungal pathogen Fusarium oxysporum f. sp. medicaginis during colonisation of resistant and susceptible Medicago truncatula hosts identifies differential pathogenicity profiles and novel candidate effectors

“…To identify genes with a high potential for involvement in pathogenicity, we set out to identify Fom genes differentially expressed between vegetative (in vitro) and in planta growth conditions with the premise that genes involved in fungal pathogenicity would be switched on or more highly and rapidly expressed upon detection of a suitable host [6, 18, 19, 31–33]. Aligned read counts (generated from the maploci and genDEseq subprocesses within the BioKanga toolkit [http://sourceforge.net/projects/biokanga/files/]) were used with a normalisation step to identify differentially expressed genes (DEGs) between each dataset (growth condition, dpi, plant accession) with EdgeR [34].…”

“…lycopersici, F. oxysporum f. sp. melonis or Fo 5176 (Brassica infecting) [6, 13, 14, 17, 18, 45–49]. SIX proteins can broadly be defined as small, generally cysteine rich, and possessing a secretion signal [13, 49].…”

“…The vascular wilt pathogen Verticillium dahliae also contains an expanded LysM effector family but the expression of only one of these is induced in planta [81]. This effector, VDAG_05180, is CDC encoded and contributes to virulence on tomato, while the remaining LysM-domain proteins are core chromosome located, not expressed during infection and single deletion mutants have no effect on virulence [18, 81]. While the roles of the latter putative V. dahliae LysM effectors remains ambiguous, the in planta up-regulated expression of Fom _ 16301 and Fom _ 04092 suggests these two SSPs may contribute to pathogenicity.…”

“…Conversely, a loss of pathogenicity or virulence can also result from the loss of all or parts of Fol Chr14 [10, 14–16]. The small Fol -4287 CDC 14 is referred to as the Fol ‘pathogenicity’ chromosome as it contains the majority of known Fol in planta expressed effectors, some of which have been shown to interfere with the host’s resistance response and/or are required for virulence [3, 9, 13, 14, 17, 18]. …”

Characterization of two homeodomain transcription factors with critical but distinct roles in virulence in the vascular pathogen Verticillium dahliae

“…Interestingly, considering the behaviour in planta of Δ vph1 , a number of genes identified as differentially expressed in WT vs. Δ vph1 coded for proteins potentially involved in the initial interaction with the host. The onset of pathogenic development is associated, for instance, with increased expression of secreted proteins (Ranganathan and Garg, ; de Sain and Rep, ). In V. dahliae , 7.4% of the genome is predicted to encode secreted proteins (Klosterman et al ., ).…”