Cell Wall Chitosaccharides Are Essential Components and Exposed Patterns of the Phytopathogenic OomyceteAphanomyces euteiches

Abstract

Chitin is an essential component of fungal cell walls, where it forms a crystalline scaffold, and chitooligosaccharides derived from it are signaling molecules recognized by the hosts of pathogenic fungi. Oomycetes are cellulosic fungus-like microorganisms which most often lack chitin in their cell walls. Here we present the first study of the cell wall of the oomycete Aphanomyces euteiches, a major parasite of legume plants. Biochemical analyses demonstrated the presence of ca. 10% N-acetyl-D-glucosamine (GlcNAc) in the cell wall. Further characterization of the GlcNAc-containing material revealed that it corresponds to noncrystalline chitosaccharides associated with glucans, rather than to chitin per se. Two putative chitin synthase (CHS) genes were identified by data mining of an A. euteiches expressed sequence tag collection and Southern blot analysis, and full-length cDNA sequences of both genes were obtained. Phylogeny analysis indicated that oomycete CHS diversification occurred before the divergence of the major oomycete lineages. Remarkably, lectin labeling showed that the Aphanomyces euteiches chitosaccharides are exposed at the cell wall surface, and study of the effect of the CHS inhibitor nikkomycin Z demonstrated that they are involved in cell wall function. These data open new perspectives for the development of antioomycete drugs and further studies of the molecular mechanisms involved in the recognition of pathogenic oomycetes by the host plants.

How belowground interactions contribute to the coexistence of mycorrhizal and non-mycorrhizal species in severely phosphorus-impoverished hyperdiverse ecosystems

“…There is some evidence that cluster roots of Embothrium coccineum (Proteaceae) function in a similar manner (Delgado et al 2015). Interestingly, the chitinases released by cluster roots of L. albus (Weisskopf et al 2006) are ineffective against the cell walls of oomycetes (water moulds) such as Phytophthora and Pythium, because of their different cell-wall structure (Badreddine et al 2008;Wessels 1994). Therefore, oomycetes, rather than fungi or bacteria, likely are the major pathogens affecting Proteaceae in hyperdiverse systems Laliberté et al 2015).…”

Analyses of Extracellular Carbohydrates in Oomycetes Unveil the Existence of Three Different Cell Wall Types

“…chitin (6)(7)(8)30). It is only in later work that some species have been shown to contain minor amounts of chitin (Ͻ0.5%) or up to 10% of other GlcNAc-based carbohydrates (16,31,32). From these data, a general concept that all oomycete cell walls are similar has emerged.…”

“…This somewhat contradicts the earlier conclusion that A. euteiches cell walls are devoid of chitin. Indeed, in the report from Badreddine et al (32), it was proposed that the cell wall GlcNAc residues in A. euteiches arise from soluble carbohydrates that may be covalently linked to glucans rather than from free crystalline chitin.…”

Hydrogen peroxide scavenging mechanisms are components of Medicago truncatula partial resistance to Aphanomyces euteiches

“…M. truncatula seed germination took place as described by Djébali et al (2009). A. euteiches (strain ATCC201684) culture conditions and inoculum preparation were performed using the protocol described by Badreddine et al (2008).…”