Download Abstract

S15-07
Transgenic elevation of beta-carotene in cassava storage roots
impacts dry matter content through transcriptional suppression of
ADP-glucose pyrophosphorylase
Getu Beyene1*, Narayanan Narayanan1, Raj Deepika Chauhan1, Felix Solomon2, Dimuth
Siritunga3, Eliana Gaitan-Solis1, John Jifon4, Nigel J. Taylor1, Paul Anderson1 and Edgar
Cahoon2
1) Donald Danforth Plant Science Center, 975 North Warson Road, St. Louis, MO 63132 USA,
2) Center for Plant Science Innovation and Department of Biochemistry, University of Nebraska, Lincoln, 1901 Vine
Street, Lincoln, NE 68588 USA,
3) Department of Biology, University of Puerto Rico, Mayaguez, PR 00680, USA,
4) Department of Horticultural Sciences, Texas A&M University System, 2415 East Highway 83, Weslaco, TX 78596
USA.
*Email: [email protected], Registrant ID# 4777
The starchy storage root of cassava (Manihot esculenta Crantz) is a main source of calories for
about half a billion people living in the tropics. This important staple food crop is deficient
however in vitamin A and several minerals such that dependence on this crop as a sole source
of food can result in micronutrient deficiencies. Using transgenic technologies, provitamin A
biofortification of cassava storage roots was achieved by co-expression of the bacterial
phytoene synthase (crtB) and A. thaliana 1-deoxy-D-xylulose 5-phosphate synthase (DXS) genes
under control of the patatin type I promoter. Overexpression of these genes was achieved in
the model cultivar 60444, and two farmer-preferred cultivars TME 204 and TME 7. Analysis of
over 200 independent transgenic lines in confined field trials in Puerto Rico demonstrated that
significant elevation of total storage root carotenoids (up to 25 ppm in 60444 and 40-50 ppm in
TME 204 and TME 7 on dry weight basis) from a baseline of less than 3 ppm in the respective
wild-types. . Additional analysis of these storage roots revealed an inverse relationship between
carotenoid accumulation and storage root dry matter content, with the highest accumulators
having up to 50% reduction in dry matter content. Data from storage root transcriptome and
biochemical analysis will be presented to show differential expression in multiple metabolic
pathways between transgenic carotenoid accumulating and non-transgenic plant lines. These
include an increase in sucrose, oil content and apocarotenoids such as abscisic acid, and a
decrease in starch content. Consistent with this, transcriptional profiling of carotenoidaccumulating roots supported by virus-induced gene silencing point to the rate limiting enzyme
in starch biosynthesis Manihot esculenta ADP-glucose pyrophophorylase (MeAGPL3) as a
critical determinant in carbon resource distribution in the roots.