Abstract
BackgroundEnzymes involved in carbohydrate metabolism include Carbohydrate esterases (CE), Glycoside hydrolases (GH), Glycosyl transferases (GT), and Polysaccharide lyases (PL), commonly referred to as carbohydrate-active enzymes (CAZymes). The CE, GH, and PL superfamilies are also known as cell wall degrading enzymes (CWDE) due to their role in the disintegration of the plant cell wall by bacterial and fungal pathogens. In Phytophthora infestans, penetration of the plant cells occurs through a specialized hyphal structure called appressorium; however, it is likely that members of the genus Phytophthora also use CWDE for invasive growth because hyphal forces are below the level of tensile strength exhibited by the plant cell wall. Because information regarding the frequency and distribution of CAZyme coding genes in Phytophthora is currently unknown, we have scanned the genomes of P. infestans, P. sojae, and P. ramorum for the presence of CAZyme-coding genes using a homology-based approach and compared the gene collinearity in the three genomes. In addition, we have tested the expression of several genes coding for CE in cultures grown in vitro.ResultsWe have found that P. infestans, P. sojae and P. ramorum contain a total of 435, 379, and 310 CAZy homologs; in each genome, most homologs belong to the GH superfamily. Most GH and PL homologs code for enzymes that hydrolyze substances present in the pectin layer forming the middle lamella of the plant cells. In addition, a significant number of CE homologs catalyzing the deacetylation of compounds characteristic of the plant cell cuticle were found. In general, a high degree of gene location conservation was observed, as indicated by the presence of sequential orthologous pairs in the three genomes. Such collinearity was frequently observed among members of the GH superfamily. On the other hand, the CE and PL superfamilies showed less collinearity for some of their putative members. Quantitative PCR experiments revealed that all genes are expressed in P. infestans when this pathogen grown in vitro. However, the levels of expression vary considerably and are lower than the expression levels observed for the constitutive control.ConclusionsIn conclusion, we have identified a highly complex set of CAZy homologs in the genomes of P. infestans, P. sojae, and P. ramorum, a significant number of which could play roles critical for pathogenicity, by participating in the degradation of the plant cell wall.
Highlights
Enzymes involved in carbohydrate metabolism include Carbohydrate esterases (CE), Glycoside hydrolases (GH), Glycosyl transferases (GT), and Polysaccharide lyases (PL), commonly referred to as carbohydrateactive enzymes (CAZymes)
The CAZyome of Phytophthora spp Scanning of the P. infestans genome for the presence of CAZyme-coding gene homologs resulted in a set of 435 sequences
Preliminary experiments with highly specific gene primers indicate that all these genes are expressed in cultures grown in vitro, albeit at different rates
Summary
Enzymes involved in carbohydrate metabolism include Carbohydrate esterases (CE), Glycoside hydrolases (GH), Glycosyl transferases (GT), and Polysaccharide lyases (PL), commonly referred to as carbohydrateactive enzymes (CAZymes). Phytophthora infestans, the causal agent of potato late blight, and as such, a major contributor to the Irish Potato Famine, is believed to cause annual losses worldwide surpassing $6.8 billion. This is a conservative estimate corresponding to the loss of approximately 15% of the global production of potato (20 Mha), valued about $45.4 billion [1]. The ability to overcome control alternatives that had been successful previously is probably due to P. infestans’ genome plasticity, as evidenced by the presence of multiple isozyme genotypes in sexual populations [12]. Evidence indicative of P. infestans’s ability to undergo genome-wide changes and adaptations was originally reported by Torto et al [14], who identified a large number of secreted proteins from EST data sets, some of which could influence the infection process and manipulate the host plant response to the pathogen
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