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JXB Advance Access originally published online on February 5, 2008
Journal of Experimental Botany 2008 59(2):213-223; doi:10.1093/jxb/erm299
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© 2008 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

Effect of the cauliflower Or transgene on carotenoid accumulation and chromoplast formation in transgenic potato tubers

Alex B. Lopez1, Joyce Van Eck2, Brian J. Conlin2, Dominick J. Paolillo3, Jennifer O'Neill1 and Li Li1,*

1USDA-ARS, Plant, Soil and Nutrition Laboratory, Cornell University, Ithaca, NY 14853, USA
2Boyce Thompson Institute for Plant Research, Cornell University, Ithaca, NY 14853, USA
3Department of Plant Biology, Cornell University, Ithaca, NY 14853, USA

* To whom correspondence should be addressed. E-mail: ll37{at}cornell.edu

Transgenic plants have facilitated our understanding of the functional roles of genes and the metabolic processes affected in plants. Recently, the Or gene was isolated from an orange cauliflower mutant and it was shown that the Or gene could serve as a novel genetic tool to enrich carotenoid content in transgenic potato tubers. An in-depth characterization of these Or transgenic lines is presented here. It was found that the Or transgene may facilitate the identification of potential rate-limiting step(s) of the carotenoid biosynthetic pathway. The Or transgenic tubers accumulated not only increased levels of carotenoids that normally are present in the controls, but also three additional metabolite intermediates of phytoene, phytofluene, and {zeta}-carotene, indicating that the desaturation steps became limiting following the expression of the Or transgene. Moreover, we observed that long-term cold storage greatly enhanced carotenoid content in the Or transgenic tubers to a level of 10-fold over controls. Expression of the Or transgene in the transgenic plants caused no dramatic changes in the transcript levels of the endogenous carotenoid biosynthetic genes, which is in agreement with the Or gene not directly controlling carotenoid biosynthesis. Microscope analysis revealed that the Or transgene conferred the formation of chromoplasts containing carotenoid sequestering structures in a heterologous system. Such structures were not observed in tubers of potato cultivars that accumulate high levels of carotenoids. Collectively, these results provide direct evidence demonstrating that the Or gene indeed controls chromoplast differentiation and that regulation of chromoplast formation can have a profound effect on carotenoid accumulation in plants.

Key words: Carotenoids, cauliflower Or gene, chromoplasts, carotenoid sequestering structures, potato

Received 15 August 2007; Revised 5 October 2007 Accepted 5 November 2007


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