Abstract
Infection of barley with the powdery mildew causal agent, Blumeria graminis f. sp. hordei (Bgh), can lead to devastating damage to barley crops. The recent emergence of fungicide resistance imposes a need to develop new antifungal strategies. The enzymes involved in cell wall biosynthesis are ideal targets for the development of fungicides. However, in order to narrow down any target proteins involved in cell wall formation, a greater understanding of the cell wall structure and composition is required. Here, we present a detailed carbohydrate analysis of the Bgh conidial cell wall, a full annotation of Carbohydrate Active enZymes (CAZy) in the Bgh genome, and a comprehensive expression profile of the genes involved in cell wall metabolism. Glycosidic linkage analysis has revealed that the cell wall polysaccharide fraction of Bgh conidia predominantly consists of glucosyl residues (63.1%) and has a greater proportion of galactopyranosyl residues compared to other species (8.5%). Trace amounts of xylosyl residues were also detected, which is unusual in ascomycetes. Transcripts of the genes involved in cell wall metabolism show high expression of chitin deacetylases, which assist fungi in evading the host defence system by deacetylating chitin to chitosan. The data presented suggest that the cell wall components of the conidia and the corresponding obligate biotrophic CAZy gene profile play a key role in the infection process.
Highlights
Plant pathogens present significant constraints on the yield and quality of agricultural crops
Linkage analysis conducted on the Blumeria graminis f. sp. hordei (Bgh) conidia showed that a majority of the conidial cell wall polysaccharides consist of glucosyl residues (Glc) (63.1%) followed by mannosyl (Man) (16.2%), galactosyl (Gal) (10.7%), N-acetylglucosaminyl (GlcNAc) (9%) and xylosyl (1%) residues (Fig. 1)
Almost all of the GlcNAc fraction of the cell wall consisted of 1,4-linked residues (97.7%), the remaining corresponded to terminal GlcNAc (3.3%)
Summary
Plant pathogens present significant constraints on the yield and quality of agricultural crops. Powdery mildew infestations in barley are caused by Blumeria graminis f. In many parts of the world powdery mildew has emerged as one of the most economically important barley diseases, as a single outbreak alone can cause up to 20–40% yield loss (Akhkha, 2009; Murray and Brennan, 2010). One of the most common strategies to control fungal pathogens is by breeding disease resistant cultivars that can detect the pathogen and avoid infection. While disease resistant breeding is a viable strategy it is a time-consuming process and may not even benefit in the long run as some resistant cultivars have shown reductions in yield performance. In conjunction with breeding resistant cultivars, an arsenal of fungicides are used to control disease outbreaks. The emergence of fungicide-resistant strains is a global issue necessitating the need for new antifungal strategies
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