title: Oxidation of the phytoalexin maackiain to 6,6-dihydroxy-maackiain by Colletotrichum gloeosporioides.
abstract: Phytoalexins are low molecular weight antibiotic compounds produced by plants in response to infection by microbes. These antimicrobial compounds are thought to provide resistance to microbial invasion and colonization. (-)Maackiain and its pterocarpan relatives can be oxidized at a number of sites, including at the 6 carbon. A previously unknown metabolite was produced for (-)maackiain by the broad host-range pathogen Colletotrichum gloeosporioides (Glomerella cingulata). This unknown was identified by LC-MS-MS and NMR spectroscopy to be 6,6a-di-OH-maackiain (3,6,6a-trihydroxy-8,9,methylenedioxy-pterocarpan). It is produced by isolates that represent all four races and pathotypes of C. gloeosporioides isolated from the tropical forage legume Stylosanthes spp. We present evidence that the primary metabolite (-)6a-OH-maackiain is subsequently hydroxylated at carbon 6, a step resulting in a compound that is increased in polarity and decreased in toxicity relative to the parent compound and (-)6a-OH-maackiain. This further oxidation may be required for efficient excretion or carbon source scavenging.
authors.affiliation: Department of Plant Pathology, University of Arizona, Tucson 85721, USA.
authors.forename: S
authors.initials: S
authors.lastname: Soby
authors.forename: R
authors.initials: R
authors.lastname: Bates
authors.forename: H
authors.initials: H
authors.lastname: van Etten
mesh_terms: D001572:Benzofurans / Q000737:chemistry / Q000378:metabolism*; D001578:Benzopyrans / Q000737:chemistry / Q000378:metabolism*; D003904:Mitosporic Fungi / Q000378:metabolism*; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010936:Plant Extracts / Q000378:metabolism*; D018517:Plant Roots; D010944:Plants / Q000382:microbiology*; D006109:Poaceae; D036343:Pterocarpans; D012717:Sesquiterpenes; D013729:Terpenes; D000094162:Phytoalexins
chemical_list: C107202:6,6a-dihydroxymaackiain; D001572:Benzofurans; D001578:Benzopyrans; D010936:Plant Extracts; D036343:Pterocarpans; D012717:Sesquiterpenes; D013729:Terpenes; C001449:inermin; D000094162:Phytoalexins