Ketocarotenoid formation in transgenic potato

Abstract

Potato has been genetically engineered for the production of commercially important ketocarotenoids including astaxanthin (3,3'-dihydroxy 4,4'-diketo-beta-carotene). To support the formation of 3-hydroxylated and 4-ketolated beta-carotene, a transgenic potato line accumulating zeaxanthin due to inactivated zeaxanthin epoxidase was co-transformed with the crtO beta-carotene ketolase gene from the cyanobacterium Synechocystis under a constitutive promoter. Plants were generated which exhibited expression of this gene, resulting in an accumulation of echinenone, 3'-hydroxyechinenone, and 4-ketozeaxanthin in leaves, as well as 3'-hydroxyechinenone, 4-ketozeaxanthin together with astaxanthin in the tuber. The amount of ketocarotenoids formed represent approximately 10-12% of total carotenoids in leaves and tubers. Negative effects on photosynthesis due to the presence of the ketocarotenoids in leaves could be excluded by the determination of variable fluorescence.

Transcriptional-Metabolic Networks in β-Carotene-Enriched Potato Tubers: The Long and Winding Road to the Golden Phenotype

“…The second one was a "push" strategy and relied on the overexpression of biosynthetic genes in a constitutive or tuber-specific manner. This included the overexpression of single genes such as CrtB (Ducreux et al, 2005), of 1-deoxy-D-xylulose 5-phosphate synthase (involved in the synthesis of the isoprenoid precursor IPP; Morris et al, 2006b) or of b-carotene ketolase (Morris et al, 2006a; resulting in the production of ketocarotenoids), or of combinations of two or three genes (minipathways; Gerjets and Sandmann, 2006;Diretto et al, 2007a). The third strategy, termed "sink engineering," relied on the overexpression of regulatory genes causing differentiation of chromoplasts, which in turn act as storage structures for carotenoids (Lopez et al, 2008).…”

Pigment Biosynthesis II: Betacyanins and Carotenoids

“…Because wild-type potato tubers do not contain zeaxanthin, a substrate of ␤-ketolase to produce ketocarotenoids, crtO was re-introduced into a transgenic potato accumulating zeaxanthin by inactivation of zeaxanthin epoxidase (Römer et al, 2002;Gerjets and Sandmann, 2006). Transgenic plants expressing crtO constitutively accumulated several types of ketocarotenoids including astaxanthin, echinenone, 3 -hydroxyechinenone, and 4-ketozeaxanthin in tubers.…”

Pathway engineering of plants toward astaxanthin production

“…This finding coincides with our results of the complementation experiments using E. coli transformants. As for practical plants, several ketolase genes were tried to be expressed in several crops, i.e., tomato, potato and carrot plants (Rally et al 2004;Morris et al 2006;Gerjets and Sandmann 2006;Jayaraj et al 2008). The bkt1 and crtO genes were individually introduced into potato plants, and resultant transgenic plants were found to produce ketocarotenoids including astaxanthin in the tuber tissues (Morris et al 2006;Gerjets and Sandmann 2006), as shown in Table 1.…”

“…As for practical plants, several ketolase genes were tried to be expressed in several crops, i.e., tomato, potato and carrot plants (Rally et al 2004;Morris et al 2006;Gerjets and Sandmann 2006;Jayaraj et al 2008). The bkt1 and crtO genes were individually introduced into potato plants, and resultant transgenic plants were found to produce ketocarotenoids including astaxanthin in the tuber tissues (Morris et al 2006;Gerjets and Sandmann 2006), as shown in Table 1. Jayaraj et al (2008) expressed the bkt1 gene in carrot roots using the double CaMV 35S promoter, and found that the transgenic roots were able to accumulate large amounts of ketocarotenoids (236 mg g Ϫ1 fresh weight; 68% of total carotenoids) containing 91.6 mg g Ϫ1 fresh weight of astaxanthin, 57.0 mg g Ϫ1 fresh weight of adonirubin and 50.1 mg g Ϫ1 fresh weight of canthaxanthin (Table 1).…”