Developmentally regulated conversion of surface‐exposed chitin to chitosan in cell walls of plant pathogenic fungi

Abstract

Summary• Conversion of surface-exposed chitin to chitosan in cell walls of in vitro -and in vivo -differentiated infection structures of two rust fungi, the wheat stem rust fungus Puccinia graminis f. sp. tritici and the broad bean rust fungus Uromyces fabae , and of the causal agent of maize anthracnose, Colletotrichum graminicola , were studied.• Epi-fluorescence microscopy with the fluorescence-labeled lectin wheat germ agglutinin (WGA) revealed that surfaces of infection structures formed on the plant cuticle expose chitin, whereas surfaces of structures formed after invading the host do not.• To identify chitin modification by de-N -acetylation, we raised polyclonal antibodies specifically recognizing de-N -acetylated chitosan. These antibodies labeled only those infection structures that differentiate inside the plant, indicating that chitosan is exposed on cell wall surfaces post penetration.• Surface modification of the fungal cell walls by chitin de-N -acetylation is discussed as a fungal strategy to protect cell walls of pathogenic hyphae from enzymatic hydrolysis by host chitinases, and to avoid generation of an auto-catalytic defense response system in the invaded host tissue.

Structure and Mechanism of Chitin Deacetylase from the Fungal Pathogen Colletotrichum lindemuthianum,

“…The first strand of ClCDA ( 1) and equivalent BsPdaA ( 2) is topologically equivalent to the final strand of the barrel in SpPgdA ( 17, Figure 1A). Indeed, so far all of the structurally defined members of the CE-4 family adopt a degree of "secondary structure swapping" from the canonical CE-4 ( /R) 8 fold.…”

“…The first structure of a CE-4 family member, B. subtilis PdaA, was reported recently (33). The protein adopts a ( /R) 8 fold with a putative substratebinding groove harboring the majority of the conserved residues. The data obtained from soaking studies proved inconclusive as to possible metal/substrate-binding sites.…”

Chitin and chitin-related compounds in plant–fungal interactions

“…Lack or degradation of surface α-1,3-glucan increased fungal susceptibility towards chitinase, suggesting the protective role of α-1,3-glucan against plants’ antifungal enzymes during infection (Fujikawa et al 2012). Alternatively, during host colonisation, some fungi convert cell wall chitin by deaminases into chitosan, which is a poor substrate for chitinases and a weak inducer of plant immune responses (El Gueddari et al 2002). …”

Perspectives of Chitin Deacetylase Research

“…CDAs have been biologically confirmed to be an essential enzyme required for proper spore formation (Matsuo et al 2005, Christodoulidou et al 1996, Christodoulidou et al 1999, cell wall integrity (Baker et al 2007), and self-protection through conversion of nascent chitin into chitosan (El Gueddari et al 2002, Blair et al 2006. The extracellular CDAs produced by the entomopathogenic fungus Metarhizium anisopliae was suggested to own a dual role in modifying the insect cuticular chitin for easy penetration as well as for altering its own cell walls for defense from insect chitinase (Nahar et al 2004).…”