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JXB Advance Access published online on July 26, 2006
Journal of Experimental Botany, 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.
Received January 11, 2006
Accepted May 25, 2006

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. Morris 1, Laurence J. M. Ducreux 1, Peter Hedden 2, Steve Millam 3, and Mark A. Taylor 1 *

1 Quality, Health and Nutrition, Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, UK
2 Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, UK
3 Gene Expression, Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, UK; Present address: Daniel Rutherford Building, Institute of Molecular Plant Sciences, Kings Buildings, University of Edinburgh, Edinburgh EH9 3JR, UKPresent address: Daniel Rutherford Building, Institute of Molecular Plant Sciences, Kings Buildings, University of Edinburgh, Edinburgh EH9 3JR, UK

* To whom correspondence should be addressed.
Mark A. Taylor, E-mail: mtaylo{at}scri.sari.ac.uk


  Abstract

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.

Keywords: Cytokinin; 1-deoxy-D-xylulose 5-phosphate synthase; dormancy; isoprenoid; potato; sprouting.
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