Metabolic engineering of high carotenoid potato tubers containing enhanced levels of -carotene and lutein

Abstract

In order to enhance the carotenoid content of potato tubers, transgenic potato plants have been produced expressing an Erwinia uredovora crtB gene encoding phytoene synthase, specifically in the tuber of Solanum tuberosum L. cultivar Désirée which normally produces tubers containing c. 5.6 μg carotenoid g⁻¹ DW and also in Solanum phureja L. cv. Mayan Gold which has a tuber carotenoid content of typically 20 μg carotenoid g⁻¹ DW. In developing tubers of transgenic crtB Désirée lines, carotenoid levels reached 35 μg carotenoid g⁻¹ DW and the balance of carotenoids changed radically compared with controls: β-carotene levels in the transgenic tubers reached c. 11 μg g⁻¹ DW, whereas control tubers contained negligible amounts and lutein accumulated to a level 19-fold higher than empty-vector transformed controls. The crtB gene was also transformed into S. phureja (cv. Mayan Gold), again resulting in an increase in total carotenoid content to 78 μg carotenoid g⁻¹ DW in the most affected transgenic line. In these tubers, the major carotenoids were violaxanthin, lutein, antheraxanthin, and β-carotene. No increases in expression levels of the major carotenoid biosynthetic genes could be detected in the transgenic tubers, despite the large increase in carotenoid accumulation. Microarray analysis was used to identify a number of genes that were consistently up- or down-regulated in transgenic crtB tubers compared with empty vector controls. The implications of these data from a nutritional standpoint and for further modifications of tuber carotenoid content are discussed.