|Van Eck, Joyce|
Submitted to: Journal of Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/5/2007
Publication Date: 2/5/2008
Citation: Lopez, A., Van Eck, J., Conlin, B., Paolillo, D., O'Neill, J., Li, L. 2008. Effect of the cauliflower Or transgene on carotenoid accumulation and chromoplast formation in transgenic potato tubers. Journal of Experimental Botany. 59:213-223. Interpretive Summary: Plant carotenoids are the primary dietary source of provitamin A for humans and play an important role in reducing the incidence of some chronic diseases. Biofortification of staple crops with increased levels of carotenoids is considered to be a very effective and sustainable approach to improve human nutrition and health. Current approach primarily relies on expression of the biosynthetic genes which in many cases limits our capacity to enhance carotenoids to significant levels. Our work demonstrates that creating a metabolic sink by inducing the formation of sequestering structures exerts a profound effect on carotenoid accumulation. We believe that manipulation of sink capacity along with catalytic activity is the promising strategy to maximally enhance carotenoid levels in staple crops to the levels required for optimal human nutrition and health.
Technical Abstract: Transgenic plants have facilitated our understanding of the functional roles of genes and the metabolic processes affected in plants. Recently, we isolated the Or gene from an orange cauliflower mutant and showed that the Or gene could serve as a novel genetic tool to enrich carotenoid content in transgenic potato tubers. Here we present an in-depth characterization of these Or transgenic lines. We found that the Or transgene may facilitate the identification of potential rate-limiting step(s) of 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 '-carotene, pointing 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 agreeable with the Or gene not directly controlling carotenoid biosynthesis. Microscope analysis revealed that the Or transgene confers 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.