Different mechanisms for phytoalexin induction by pathogen and wound signals in Medicago truncatula
- Marina Naoumkina*,
- Mohamed A. Farag*,†,
- Lloyd W. Sumner*,
- Yuhong Tang*,
- Chang-Jun Liu‡, and
- Richard A. Dixon*,§
- *Plant Biology Division, Samuel Roberts Noble Foundation, 2510 Sam Noble Parkway, Ardmore, OK 73401,
- †Department of Pharmacognosy, Faculty of Pharmacy, Cairo University, Kasr El Aini Street, Cairo, Egypt; and
- ‡Department of Biology, Brookhaven National Laboratory, Upton, NY 11973
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Contributed by Richard A. Dixon, September 13, 2007 (received for review July 1, 2007)
Abstract
Cell suspensions of the model legume Medicago truncatula accumulated the isoflavonoid phytoalexin medicarpin in response to yeast elicitor or methyl jasmonate (MJ), accompanied by decreased levels of isoflavone glycosides in MJ-treated cells. DNA microarray analysis revealed rapid, massive induction of early (iso)flavonoid pathway gene transcripts in response to yeast elicitor, but not MJ, and differential induction by the two elicitors of sets of genes encoding transcription factors, ABC transporters, and β-glucosidases. In contrast, both elicitors induced genes encoding enzymes for conversion of the isoflavone formononetin to medicarpin. Four MJ-induced β-glucosidases were expressed as recombinant enzymes in yeast, and three were active with isoflavone glucosides. The most highly induced β-glucosidase was nuclear localized and preferred flavones to isoflavones. The results indicate that the genetic and biochemical mechanisms underlying accumulation of medicarpin differ depending on the nature of the stimulus and suggest a role for MJ as a signal for rapid hydrolysis of preformed, conjugated intermediates for antimicrobial biosynthesis during wound responses.
Footnotes
- §To whom correspondence should be addressed. E-mail: radixon{at}noble.org
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Author contributions: M.N. and R.A.D. designed research; M.N., M.A.F., Y.T., and C.-J.L. performed research; L.W.S. contributed new reagents/analytic tools; M.N., M.A.F., L.W.S., Y.T., C.-J.L., and R.A.D. analyzed data; and R.A.D. wrote the paper.
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This contribution is part of the special series of Inaugural Articles by members of the National Academy of Sciences elected on May 1, 2007.
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The authors declare no conflict of interest.
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Data deposition: The sequences reported in this paper have been deposited in the GenBank database (accession nos. EU078901–EU078904).
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This article contains supporting information online at www.pnas.org/cgi/content/full/0708697104/DC1.
- Abbreviations:
- YE,
- yeast elicitor;
- MJ,
- methyl jasmonate;
- TC,
- tentative consensus;
- PAL,
- l-phenylalanine ammonia-lyase;
- CHS,
- chalcone synthase;
- 2HID,
- 2-hydroxyisoflavanone dehydratase;
- CHI,
- chalcone isomerase;
- Gn,
- glucosidase n;
- pNPG,
- p-nitrophenyl glucoside.
- © 2007 by The National Academy of Sciences of the USA
