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JXB Advance Access originally published online on July 26, 2006
Journal of Experimental Botany 2006 57(12):3007-3018; doi:10.1093/jxb/erl061
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© 2006 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

Overexpression of a bacterial 1-deoxy-D-xylulose 5-phosphate synthase gene in potato tubers perturbs the isoprenoid metabolic network: implications for the control of the tuber life cycle

Wayne L. Morris1, Laurence J. M. Ducreux1, Peter Hedden2, Steve Millam3 * and Mark A. Taylor1,{dagger}

1Quality, Health and Nutrition, Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, UK
2Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, UK
3Gene Expression, Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, UK

{dagger}To whom correspondence should be addressed. E-mail: mtaylo{at}scri.sari.ac.uk

Potato tubers were engineered to express a bacterial gene encoding 1-deoxy-D-xylulose 5-phosphate synthase (DXS) in order to investigate the effects of perturbation of isoprenoid biosynthesis. Twenty-four independent transgenic lines out of 38 generated produced tubers with significantly elongated shape that also exhibited an early tuber sprouting phenotype. Expression analysis of nine transgenic lines (four exhibiting the phenotype and five showing a wild-type phenotype) demonstrated that the phenotype was strongly associated with dxs expression. At harvest, apical bud growth had already commenced in dxs-expressing tubers whereas in control lines no bud growth was evident until dormancy was released after 56–70 d of storage. The initial phase of bud growth in dxs tubers was followed by a lag period of ~56 d, before further elongation of the developing sprouts could be detected. Thus dxs expression results in the separation of distinct phases in the dormancy and sprouting processes. In order to account for the sprouting phenotype, the levels of plastid-derived isoprenoid growth regulators were measured in transgenic and control tubers. The major difference measured was an increase in the level of trans-zeatin riboside in tubers at harvest expressing dxs. Additionally, compared with controls, in some dxs-expressing lines, tuber carotenoid content increased ~2-fold, with most of the increase accounted for by a 6–7-fold increase in phytoene.

Key words: Cytokinin, 1-deoxy-D-xylulose 5-phosphate synthase, dormancy, isoprenoid, potato, sprouting


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