Expression Profiles of Genes Involved in the Carotenoid Biosynthetic Pathway in Yellow-Fleshed Potato Cultivars (Solanum tuberosum L.) from South Korea

Efforts are being made to identify a parental cultivar suitable for metabolic engineering of potato (Solanum tuberosum L.) that will elevate total carotenoid content or produce a specific type of carotenoid. As an initial step in this search, we performed high performance liquid chromatography analyses and comparisons among gene expression profiles for several cultivars domesticated or bred in South Korea. Here, the dark yellow-fleshed "Golden Valley" contained the highest level of total carotenoids (23.8 mu g g(-1) dry weight (DW)), which was 1.7- to 3.7-fold higher than those measured in other cultivars. The predominant carotenoids in "Golden Valley" were lutein (40.3% of the total), violaxanthin (29.8%), and beta-carotene (8.8%), with only a trace amount of zeaxanthin (0.02%) being detected. Levels of lutein and beta-carotene in that cultivar were significantly higher than in the others. Interestingly, relatively high amounts of violaxanthin were accumulated in all cultivars, ranging from 15.9% (1.0 mu g g(-1) DW in "Jowon") to 61.7% (8.2 mu g g(-1) DW in "Dejima"). In accordance with the relatively high content of total carotenoids in "Golden Valley", remarkably elevated transcripts were also accumulated for most of the genes involved in the carotenoid biosynthetic pathway. In particular, genes encoding enzymes for the first three steps of carotenogenesis-phytoene synthase, phytoene desaturase, and zeta-carotene desaturase-were most actively expressed. A relatively high level of transcript for the carotene hydroxylase (Chy2) gene was detected in all cultivars, including "Jowon", which had accumulated the lowest amount of total carotenoids. In contrast, almost no transcripts were detected for carotene isomerase (CrtIso) and Chy1 in any of these cultivars. Our preliminary results suggest that "Golden Valley" is an excellent candidate for metabolic engineering that further increases its content of specific carotenoids, e.g., beta-carotene and astaxanthin.