Submitted to: American Journal of Potato Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/4/2007
Publication Date: 9/25/2007
Citation: Van Eck, J., Conlin, B., Garvin, D.F., Mason, H., Navarre, D.A., Brown, C.R. 2007. Enhancing beta-carotene content in potato by RNAi-mediated silencing of the b-carotene hydroxylase gene. American Journal of Potato Research. 84:331-342. Interpretive Summary: Vitamin A in human diets comes largely from plants, in the form of beta-carotene. However, vitamin A deficiency is a widespread and serious malnutrition problem that leads to a spectrum of maladies and diseases in humans. In large part, the occurrence of vitamin A deficiency is due to the fact that many staple crops that humans rely upon contain very little beta-carotene. New strategies to increase the content of vitamin A in these staple crops will provide a crop-based avenue for reducing vitamin A deficiency. Potato is an important staple crop with extremely low levels of beta-carotene. In this study a plant gene that modifies beta-carotene into zeaxanthin, a new chemical compound that no longer can be used by the human body to produce vitamin A, was disabled in potato. The hypothesis being tested was that disabling this gene in potato would allow beta-carotene to accumulate. Results indicate that disabling this gene does lead to the accumulation of beta-carotene. The levels of beta-carotene that accumulated are nutritionally significant to humans who are vitamin A-deficient. The strategy for increasing beta-carotene content in crops that was devised and tested in this study provides a unique avenue for increasing beta-carotene levels in important staple crops such as potato. This in turn will lead to improved human health and well-being by reducing the widespread incidence of vitamin A deficiency.
Technical Abstract: Plant carotenoids play key roles in numerous plant functions and have a significant role in the human diet by serving as precursors for vitamin A synthesis and by reducing the incidence of certain diseases. The purpose of this work was to identify novel methods for enhancing beta-carotene content in potato, a major staple food crop. We used RNA interference (RNAi) to silence the beta-carotene hydroxylase gene (bch), which encodes the enzyme that converts beta-carotene to zeaxanthin. Agrobacterium-mediated transformation was employed to introduce two RNAi constructs into three different potato lines (Yema de Huevo, 91E22, and Desiree). One construct contained the tuber specific granule bound starch synthase (GBSS) promoter and the other contained the strong constitutive cauliflower mosaic virus 35S (CaMV 35S) promoter. Eighty-six percent of the silenced lines had altered carotenoid profiles as revealed by HPLC. Beta-carotene content was increased from trace amounts in wild type tubers up to 331 ug 100g-1 fresh weight. In addition, some transformants exhibited a significant decrease in zeaxanthin content and/or an increase in lutein. In general, transformants derived from the GBSS construct contained more beta-carotene than CaMV 35S transformants. Reverse-transcriptase PCR (RT-PCR) analysis of bch RNA abundance in tubers demonstrated that the extent of bch silencing varied between transformants and was associated with the level of beta-carotene. Similarly, RT-PCR showed that bch silencing also occurred in leaves but primarily in the CaMV 35S lines. These results demonstrate that silencing bch increased the content of health-promoting carotenoids beta-carotene and lutein in potato.