| Title: | A functional genomics investigation of allelochemical biosynthesis in Sorghum bicolor root hairs |
| Author(s): | Baerson SR; Dayan FE; Rimando AM; Nanayakkara NPD; Liu CJ; Schroder J; Fishbein M; Pan Z; Kagan IA; Pratt LH; Cordonnier-Pratt MM; Duke SO; |
| Address: | "United States Department of Agriculture, Agricultural Research Service, Natural Products Utilization Research Unit, University, Mississippi 38677. Electronic address: sbaerson@ars.usda.gov. United States Department of Agriculture, Agricultural Research Service, Natural Products Utilization Research Unit, University, Mississippi 38677. National Center for Natural Products Research, School of Pharmacy, University of Mississippi, University, Mississippi 38677. Biology Department, Brookhaven National Laboratory, Upton, New York 11973. Universitat Freiburg, Institut fur Biologie II, Schanzlestrasse 1, D-79104 Freiburg, Germany. Department of Biology, Portland State University, Portland, Oregon 97207. Department of Plant Biology, University of Georgia, Athens, Georgia 30602" |
| ISSN/ISBN: | 0021-9258 (Print) 0021-9258 (Linking) |
| Abstract: | "Sorghum is considered to be one of the more allelopathic crop species, producing phytotoxins such as the potent benzoquinone sorgoleone (2-hydroxy-5-methoxy-3-[(Z,Z)-8',11',14'-pentadecatriene]-p-benzoquinone) and its analogs. Sorgoleone likely accounts for much of the allelopathy of Sorghum spp., typically representing the predominant constituent of Sorghum bicolor root exudates. Previous and ongoing studies suggest that the biosynthetic pathway for this plant growth inhibitor occurs in root hair cells, involving a polyketide synthase activity that utilizes an atypical 16:3 fatty acyl-CoA starter unit, resulting in the formation of a pentadecatrienyl resorcinol intermediate. Subsequent modifications of this resorcinolic intermediate are likely to be mediated by S-adenosylmethionine-dependent O-methyltransferases and dihydroxylation by cytochrome P450 monooxygenases, although the precise sequence of reactions has not been determined previously. Analyses performed by gas chromatography-mass spectrometry with sorghum root extracts identified a 3-methyl ether derivative of the likely pentadecatrienyl resorcinol intermediate, indicating that dihydroxylation of the resorcinol ring is preceded by O-methylation at the 3'-position by a novel 5-n-alk(en)ylresorcinol-utilizing O-methyltransferase activity. An expressed sequence tag data set consisting of 5,468 sequences selected at random from an S. bicolor root hair-specific cDNA library was generated to identify candidate sequences potentially encoding enzymes involved in the sorgoleone biosynthetic pathway. Quantitative real time reverse transcription-PCR and recombinant enzyme studies with putative O-methyltransferase sequences obtained from the expressed sequence tag data set have led to the identification of a novel O-methyltransferase highly and predominantly expressed in root hairs (designated SbOMT3), which preferentially utilizes alk(en)ylresorcinols among a panel of benzene-derivative substrates tested. SbOMT3 is therefore proposed to be involved in the biosynthesis of the allelochemical sorgoleone" |
| Keywords: | "*Alleles Amino Acid Sequence Benzoquinones/chemistry Escherichia coli/metabolism Expressed Sequence Tags Genes, Plant *Genomics Lipids/chemistry Mass Spectrometry/methods Molecular Sequence Data Pheromones/*chemistry Phylogeny Plant Roots/*metabolism Reco;" |
| Notes: | "MedlineBaerson, Scott R Dayan, Franck E Rimando, Agnes M Nanayakkara, N P Dhammika Liu, Chang-Jun Schroder, Joachim Fishbein, Mark Pan, Zhiqiang Kagan, Isabelle A Pratt, Lee H Cordonnier-Pratt, Marie-Michele Duke, Stephen O eng 2007/11/14 J Biol Chem. 2008 Feb 8; 283(6):3231-3247. doi: 10.1074/jbc.M706587200. Epub 2007 Nov 12" |
