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GrainGenes Reference Report: MPM-13-1041

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Reference	MPM-13-1041
Title	Stagonospora avenae secretes multiple enzymes that hydrolyze oat leaf saponins
Journal	Molecular Plant Microbe Interactions
Year	2000
Volume	13
Pages	1041-1052
Author	Morrissey JP Wubben JP Osbourn AE
Abstract	Summary: The phytopathogenic fungus Stagonospora avenae is able to infect oat leaves despite the presence of avenacoside saponins in the leaf tissue. In response to pathogen attack, avenacosides are converted into 26-desglucoavenacosides (26-DGAs), which possess antifungal activity. These molecules are comprised of a steroidal backbone linked to a branched sugar chain consisting of one alpha-L-rhamnose and two (avenacoside A) or three (avenacoside B) beta-D-glucose residues. Isolates of the fungus that are pathogenic to oats are capable of sequential hydrolysis of the sugar residues from the 26-DGAs. Degradation is initiated by removal of the L-rhamnose, which abolishes antifungal activity. The D-glucose residues are then hydrolyzed by beta-glucosidase activity. A comprehensive analysis of saponin-hydrolyzing activities was undertaken, and it was established that S. avenae isolate WAC1293 secretes three enzymes, one alpha- rhamnosidase and two beta-glucosidases, that carry out this hydrolysis. The major beta-glucosidase was purified and the gene encoding the enzyme cloned. The protein is similar to saponin-hydrolyzing enzymes produced by three other phytopathogenic fungi, Gaeumannomyces graminis, Septoria lycopersici, and Botrytis cinerea, and is a family 3 beta-glucosidase. The gene encoding the beta-glucosidase is expressed during infection of oat leaves but is not essential for pathogenicity
Keyword	[ Hide all but 1 of 45 ] alpha amino acid sequence antifungal antifungal activity antifungal properties attack avena avena sativa beta-glucosidase botrytis cinerea chain chemical structure d-glucose defense mechanisms degradation enzyme family fungi fungus gaeumannomyces graminis gene graminis hydrolysis infection isolate molecules multiple oat oat leaves oats pathogen pathogen attack pathogenicity plant composition plant pathogenic fungi precursors residue residues saponins secondary metabolites secretion secretions stagonospora sugar tissue

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