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Accession IconSRP110033

Provitamin A-enriched Golden Cassava generated through metabolic engineering has reduced dry matter, elevated oil content and enhanced shelf-life

Organism Icon Manihot esculenta
Sample Icon No Downloadable Samples
Technology Badge IconIllumina HiSeq 2000

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In this study, ß-carotene concentrations in cassava storage roots were enhanced by co-expression of transgenes for deoxyxylulose-5-phosphate synthase (DXS) and bacterial phytoene synthase (crtB), mediated by the patatin type-1 promoter. Storage roots harvested from field-grown plants accumulated carotenoids to =50 µg/g DW, a 15- to 20-fold increase relative to roots from non-transgenic plants. Approximately 85-90% of these carotenoids accumulated as all-trans-ß-carotene, the most nutritionally efficacious carotenoid. ß-carotene-accumulating storage roots displayed delayed onset of post-harvest physiological deterioration, a major constraint limiting utilization of cassava products. Significant metabolite changes were detected in ß-carotene enhanced storage roots. Most significantly, an inverse correlation was observed between ß-carotene and dry matter contents, with reductions of 50% to 60% of dry matter content in the highest carotenoid accumulating storage roots of different cultivars. Further analysis confirmed concomitant reduction in starch content, and increased levels of total fatty acids, triacylglycerols, soluble sugars, and abscisic acid. Irish potato engineered to co-express DXS and crtB displayed a similar correlation between ß-carotene accumulation, reduced dry matter and starch content, and elevated oil and soluble sugars in tubers. Transcriptome analyses revealed reduced expression of starch biosynthetic genes, ADP-glucose pyrophosphorylase genes, in transgenic, carotene-accumulating cassava roots relative to non-transgenic roots. These findings highlight unintended metabolic consequences of provitamin A biofortification of starch-rich organs and point to strategies for redirecting metabolic flux to restore starch production. Overall design: Transcriptom data was generated from cassava storage roots harvetsed at 12 months after planting from confined field trial conducted in Puerto Rico. Two transgenic cassava lines DXS//PS-20 and DXS//PS-37 and a non-tranegnic control cultivar 60444 were used for the study each replicated three-times
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