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

• Published in: Journal of experimental botany 2008-02, Vol.59 (2), p.213-223
• Main Authors: Lopez, Alex B, Van Eck, Joyce, Conlin, Brian J, Paolillo, Dominick J, O'Neill, Jennifer, Li, Li
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Biological and medical sciences; Biosynthesis; Brassica; Brassica - genetics; Brassica oleracea var. botrytis; carotenoid sequestering structures; Carotenoids; Carotenoids - biosynthesis; Carotenoids - metabolism; Cauliflower; cauliflower Or gene; Chromoplasts; Cold storage; Cold Temperature; Fundamental and applied biological sciences. Psychology; Gene Expression; Genes, Plant; Genetics and breeding of economic plants; Metabolism; Or gene; Pest resistance; phytoene; phytofluene; Plant pathogens; Plant Tubers - metabolism; Plant Tubers - physiology; Plants; Plants, Genetically Modified - metabolism; Plants, Genetically Modified - physiology; Plastids - physiology; potato; potatoes; Research Papers; Solanum tuberosum; Solanum tuberosum - genetics; Solanum tuberosum - metabolism; Solanum tuberosum - physiology; Transgenes; Transgenic plants; Tubers; Varietal selection. Specialized plant breeding, plant breeding aims; zeta-carotene
• ISSN: 0022-0957; 1460-2431
• DOI: 10.1093/jxb/erm299

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 ζ-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.