Format

Send to

Choose Destination
Plant Biotechnol J. 2018 Jun;16(6):1186-1200. doi: 10.1111/pbi.12862. Epub 2017 Dec 27.

Provitamin A biofortification of cassava enhances shelf life but reduces dry matter content of storage roots due to altered carbon partitioning into starch.

Author information

1
Donald Danforth Plant Science Center, St. Louis, MO, USA.
2
Center for Plant Science Innovation, Department of Biochemistry, E318 Beadle Center, University of Nebraska-Lincoln, Lincoln, NE, USA.
3
Department of Biology, University of Puerto Rico, Mayaguez, Puerto Rico.
4
Department of Horticultural Sciences, Texas A&M AgriLife Research and Extension Center, Weslaco, TX, USA.
5
Boyce Thompson Institute, Ithaca, NY, USA.
6
New Mexico Consortium, Los Alamos National Laboratory, Los Alamos, NM, USA.

Abstract

Storage roots of cassava (Manihot esculenta Crantz), a major subsistence crop of sub-Saharan Africa, are calorie rich but deficient in essential micronutrients, including provitamin A β-carotene. In this study, β-carotene concentrations in cassava storage roots were enhanced by co-expression of transgenes for deoxy-d-xylulose-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, 15- to 20-fold increases relative to roots from nontransgenic plants. Approximately 85%-90% of these carotenoids accumulated as all-trans-β-carotene, the most nutritionally efficacious carotenoid. β-Carotene-accumulating storage roots displayed delayed onset of postharvest physiological deterioration, a major constraint limiting utilization of cassava products. Large metabolite changes were detected in β-carotene-enhanced storage roots. Most significantly, an inverse correlation was observed between β-carotene and dry matter content, with reductions of 50%-60% of dry matter content in the highest carotenoid-accumulating storage roots of different cultivars. Further analysis confirmed a concomitant reduction in starch content and increased levels of total fatty acids, triacylglycerols, soluble sugars and abscisic acid. Potato engineered to co-express DXS and crtB displayed a similar correlation between β-carotene accumulation, reduced dry matter and starch content and elevated oil and soluble sugars in tubers. Transcriptome analyses revealed a reduced expression of genes involved in starch biosynthesis including ADP-glucose pyrophosphorylase genes in transgenic, carotene-accumulating cassava roots relative to nontransgenic 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.

KEYWORDS:

cassava; dry matter; fatty acid; provitamin A; starch; β-carotene

Supplemental Content

Full text links

Icon for Wiley Icon for PubMed Central
Loading ...
Support Center