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JXB Advance Access published online on October 10, 2007
Journal of Experimental Botany, doi:10.1093/jxb/erm173
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© 2007 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details)

RESEARCH PAPER

Biosynthesis of lipid resorcinols and benzoquinones in isolated secretory plant root hairs

Franck E. Dayan1,*, Susan B. Watson1 and N. P. Dhammika Nanayakkara2

1United States Department of Agriculture, Agricultural Research Service, Natural Products Utilization Research Unit, PO Box 8048, University, MS 38677, USA
2National Center for Natural Products Research, School of Pharmacy, University of Mississippi, University, MS 38677, USA

* To whom correspondence should be addressed. E-mail: fdayan{at}olemiss.edu

The primary functions of root hairs are to increase the root surface area and to aid plants in water and nutrient uptake. However, some root hairs also have secretory functions and exude bioactive secondary metabolites. Sorghum (Sorghum bicolor) root hairs release a substantial amount of phenolic lipids including sorgoleone, a 3-pentadecatriene benzoquinone. The activity of the key enzymes involved in the biosynthesis of lipid resorcinols and benzoquinones was measured directly in isolated root hair preparations obtained from 6-d-old roots. The purified root hair preparation readily converted long-chain acyl-CoA starter units to their corresponding lipid resorcinols and decanoyl-CoA was the best substrate, yielding a 5-n-nonyl-resorcinol. The isolated root hair preparation also had high S-adenosyl-L-methionine-dependent O-methyltransferase activity, which catalyses the methylation of several 5-n-alkyl-resorcinols. Optimum activity was with 5-n-pentyl-resorcinol. Isolated root hairs also exhibited hydroxylase activity (putatively a P450 mono-oxygenase) that reacted with the lipophilic 5-pentadecyl-resorcinol substrate. The in situ hydroxylase activity was low relative to the other enzymes studied, but was still detectable in isolated root hairs. Thus, sorghum root hairs possess the entire metabolic machinery necessary for the biosynthesis of lipid resorcinols and benzoquinones. This will have implications for the genetic engineering of bioactive lipid resorcinols and benzoquinones in sorghum and in other plant species. It also demonstrates that some root hairs can function as specialized cells for the production of bioactive secondary metabolites.

Key words: Alkyl-resorcinols, allelopathy, essential oil, hydroxylase, O-methyltransferase, P450 mono-oxygenase, polyketide synthase, root hair isolation, sorgoleone

Received 16 May 2007; Revised 25 May 2007 Accepted 26 June 2007


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