Sunday, August 10, 2008
P99

Armillaria natural products: bioactivity and biosynthetic genes

Mathias T. Misiek, Pharmazeutische Biologie und Biotechnologie, Albert-Ludwigs-Universität Freiburg, Stefan-Meier-Str. 17, Freiburg, Germany, Courtney C. Aldrich, Center for Drug Design, University of Minnesota, 516 Delaware Street SE, Minneapolis, MN 55455, and Dirk Hoffmeister, Plant Pathology, University of Minnesota, 1991 Upper Buford Circle, Saint Paul, MN 55108.

The homobasidiomycete genus Armillaria is a notorious and omnipresent tree pathogen and a potent lignocellulose degrader. Armillaria is also known to produce antibiotically active natural products. A genomic cosmid library for natural product genes was screened and a potential locus for small molecule biosynthetic genes was identified, showing an extremely complex gene structure, allelic variation, and a substantial number of introns. We experimentally validated in silico predicted intron/exon junctions for accuracy. Based on 78 verified junctions, a consensus for donor and acceptor sites in Armillaria is presented, along with experimental evidence for non-canonical splice sites, introns with alternative donor or acceptor junctions, and allele-selective splicing. The reading frames show significant homologies to (1) mycotoxin efflux transporter genes, (2) phenoloxidase/laccase genes, and (3) genes for dual Cys2His2/Zn(II)2Cys6 transcriptional regulators. For all of these gene categories, this is the first report on examples from the genus Armillaria.

To investigate the biological activity of one group of Armillaria small molecules (the sesquiterpene aryl esters), six metabolites were isolated and purified from mycelial cultures. We tested the toxicity against a panel of bacteria, fungi and nematodes as well as phytotoxicity and cytotoxicity.


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