Papers by Dimuth Siritunga
NABC eBooks, 2010
C assava is an important staple crop in sub-Saharan africa. Between 1970 and 2007, its production... more C assava is an important staple crop in sub-Saharan africa. Between 1970 and 2007, its production and acreage tripled across africa and quadrupled in nigeria, the continent's and the world's largest producer (fao, 00). Sub-Saharan africa produced over million tons of fresh roots of cassava in 00, of which no less than 95% was consumed as food; the starch provides >5% of dietary energy for an estimated 00 million africans (Dorosh, 00). frequent consumers of cassava are at greater risk for malnutrition-especially deficiencies in vitamin-a, iron, and zinc-than consumers of other diets, particularly those that are cereal-based (Gegios et al., 00). a nutrition survey in cassava-consuming areas of nigeria and Kenya revealed inadequate intake of vitamin a in 3% and % and inadequate iron intake in 3% and % of preschool aged children, respectively (Gegios et al., 00). vitamin-a deficiency causes a loss of 9,000 disability-adjusted life years (DaLYs1) in nigeria and ,000 DaLYs in Kenya annually; iron deficiency causes loss of 59,000 DaLYs in nigeria and 03,000 DaLYs in Kenya (fielder, 009).
Frontiers in Plant Science, Feb 24, 2017
Cassava (Manihot esculenta Crantz), a staple crop for millions of sub-Saharan Africans, contains ... more Cassava (Manihot esculenta Crantz), a staple crop for millions of sub-Saharan Africans, contains high levels of cyanogenic glycosides which protect it against herbivory. However, cyanogens have also been proposed to play a role in nitrogen transport from leaves to roots. Consistent with this hypothesis, analyses of the distribution and activities of enzymes involved in cyanide metabolism provides evidence for cyanide assimilation, derived from linamarin, into amino acids in cassava roots. Both β-cyanoalanine synthase (CAS) and nitrilase (NIT), two enzymes involved in cyanide assimilation to produce asparagine, were observed to have higher activities in roots compared to leaves, consistent with their proposed role in reduced nitrogen assimilation. In addition, rhodanese activity was not detected in cassava roots, indicating that this competing means for cyanide metabolism was not a factor in cyanide detoxification. In contrast, leaves had sufficient rhodanese activity to compete with cyanide assimilation into amino acids. Using transgenic low cyanogen plants, it was shown that reducing root cyanogen levels is associated with elevated root nitrate reductase activity, presumably to compensate for the loss of reduced nitrogen from cyanogens. Finally, we overexpressed Arabidopsis CAS and NIT4 genes in cassava roots to study the feasibility of enhancing root cyanide assimilation into protein. Optimal overexpression of CAS and NIT4 resulted in up to a 50% increase in root total amino acids and a 9% increase in root protein accumulation. However, plant growth and morphology was altered in plants overexpressing these enzymes, demonstrating a complex interaction between cyanide metabolism and hormonal regulation of plant growth.
Journal of Agricultural and Food Chemistry, Apr 6, 2012
Cassava is a root crop that serves as a primary caloric source for many African communities despi... more Cassava is a root crop that serves as a primary caloric source for many African communities despite its low content of β-carotene (βC). Carotenoid content of roots from wild type (WT) and three transgenic lines with high βC were compared after cooking and preparation of nonfermented and fermented flours according to traditional African methods. The various methods of processing all decreased βC content per gram dry weight regardless of genotype. The greatest loss of βC occurred during preparation of gari (dry fermentation followed by roasting) from WT and transgenic lines. The quantities of βC in cooked transgenic cassava root that partitioned into mixed micelles during in vitro digestion and transported into Caco-2 cells were significantly greater than those for identically processed WT root. These results suggest that transgenic high βC cassava will provide individuals with greater quantities of bioaccessible βC.
Annual Review of Plant Biology, Jun 2, 2011
Journal of AOAC International, Sep 1, 2007
For cassava to become a safe and acceptable crop, it is necessary to reduce the cyanogen levels i... more For cassava to become a safe and acceptable crop, it is necessary to reduce the cyanogen levels in cassava foods. While this objective can be achieved by processing procedures, recent findings have shown that it is also possible to achieve it by suppression of cyanogen synthesis or by accelerating cyanogen turnover and volatilization. In 2003, cyanogen-free cultivars were generated by selective inhibition CYP79D1/D2 gene expression. The CYP79D1/D2 enzymes catalyze the first-dedicated step in cyanogen synthesis. Tissue-specific inhibition of CYP79D1/D2 expression in leaves lead to a 99% reduction in root cyanogen levels, indicating that the cyanogenic glycoside, linamarin, is synthesized in leaves and transported to roots. An alternative strategy to the reduce cyanogen content is to enhance cyanogen detoxification and cyanide volatilization during processing. This strategy has the advantage that cyanogen levels in unprocessed roots are not altered, potentially providing protection against herbivory and/or theft. To produce cultivars that promote rapid cyanide volatilization, hydroxynitrile lyase (HNL), which catalyzes the last step in cyanogenesis, was overexpressed in roots. Elevated HNL activity resulted in a 3-fold increase in the rate of cyanogen turnover. Importantly, the cyanogen content of the transformed and wild-type plants was identical, a potential benefit for farmers.
Plant Biotechnology Journal, 2004
Cassava (Manihot esculenta , Crantz) roots are the primary source of calories for more than 500 m... more Cassava (Manihot esculenta , Crantz) roots are the primary source of calories for more than 500 million people, the majority of whom live in the developing countries of Africa. Cassava leaves and roots contain potentially toxic levels of cyanogenic glycosides. Consumption of residual cyanogens (linamarin or acetone cyanohydrin) in incompletely processed cassava roots can cause cyanide poisoning. Hydroxynitrile lyase (HNL), which catalyses the conversion of acetone cyanohydrin to cyanide, is expressed predominantly in the cell walls and laticifers of leaves. In contrast, roots have very low levels of HNL expression. We have over-expressed HNL in transgenic cassava plants under the control of a double 35S CaMV promoter. We show that HNL activity increased more than twofold in leaves and 13-fold in roots of transgenic plants relative to wild-type plants. Elevated HNL levels were correlated with substantially reduced acetone cyanohydrin levels and increased cyanide volatilization in processed or homogenized roots. Unlike acyanogenic cassava, transgenic plants overexpressing HNL in roots retain the herbivore deterrence of cyanogens while providing a safer food product.
The FASEB Journal, Apr 1, 2011
<p>(NoA: Number of Alleles, H<sub>o</sub>: Observed Heterozygosity, H<sub>... more <p>(NoA: Number of Alleles, H<sub>o</sub>: Observed Heterozygosity, H<sub>T</sub>: Total Heterozygosity, G<sub>is</sub>: Inbreeding Coefficient).</p><p>Summary statistics of genetic diversity estimators at 23 SSR loci for 167 sweet potato samples.</p
<p>Eight accessions are from the agricultural experimental station in Gurabo, Puerto Rico (... more <p>Eight accessions are from the agricultural experimental station in Gurabo, Puerto Rico (GAES), 22 from the plant genetic resources conservation unit (PGRCU) in Griffin, GA (12 PR accessions and 10 known US commercial cultivars) and 137 Puerto Rico landraces across the island were analyzed. The eight groups (Group 1: olive green, Group 2: pink, Group: navy blue, Group: orange, Group: purple, Group: lime green, Group: red, and Group: blue) were determined based on STRUCTURE and Evanno <i>et al</i>. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0116184#pone.0116184-Evanno1" target="_blank">[26]</a> analysis. The colors of the branches in the dendrogram also indicates the groups while the highlight of the name refers to PRGCU (olive green), GAES (pink), US cultivars (navy blue) and PR landraces (light gray).</p
and 2007, its production and acreage tripled across africa and quadrupled in nigeria, the contine... more and 2007, its production and acreage tripled across africa and quadrupled in nigeria, the continent’s and the world’s largest producer (fao, 00 ). SubSaharan africa produced over million tons of fresh roots of cassava in 00 , of which no less than 95% was consumed as food; the starch provides > 5% of dietary energy for an estimated 00 million africans (Dorosh, 00 ). frequent consumers of cassava are at greater risk for malnutrition—especially deficiencies in vitamin-a, iron, and zinc—than consumers of other diets, particularly those that are cereal-based (Gegios et al., 0 0). a nutrition survey in cassava-consuming areas of nigeria and Kenya revealed inadequate intake of vitamin a in 3% and % and inadequate iron intake in 3% and % of pre-school-aged children, respectively (Gegios et al., 0 0). vitamin-a deficiency causes a loss of 9 ,000 disability-adjusted life years (DaLYs1) in nigeria and ,000 DaLYs in Kenya annually; iron deficiency causes loss of 59 ,000 DaLYs in nigeria and...
Nature Biotechnology, 2019
An amendment to this paper has been published and can be accessed via a link at the top of the pa... more An amendment to this paper has been published and can be accessed via a link at the top of the paper.
Frontiers in Plant Science, 2015
Zinc deficiency in humans is a serious problem worldwide with an estimated one third of populatio... more Zinc deficiency in humans is a serious problem worldwide with an estimated one third of populations at risk for insufficient zinc in diet, which leads to impairment of cognitive abilities and immune system function. The goal of this research was to increase the bioavailable zinc in the edible portion of cassava roots to improve the overall zinc nutrition of populations that rely on cassava as a dietary staple. To increase zinc concentrations, two Arabidopsis thaliana genes coding for ZIP1 and MTP1 were overexpressed with a tuber-specific or constitutive promoter. Eighteen transgenic events from four constructs, out of a total of 73 events generated, showed significantly higher zinc concentrations in the edible portion of the storage root compared to the nontransgenic controls. The zinc content in the transgenic lines ranged from 4 to 73 mg/kg dry weight (DW) as compared to the non-transgenic control which contained 8 mg/kg. Striking changes in whole plant phenotype such as smaller plant size and chlorotic leaves were observed in transgenic lines that over accumulated zinc. In a confined field trial five transgenic events grown for 12 months showed a range of zinc concentrations from 18 to 217 mg/kg DW. Although the overexpression of zinc transporters was successful in increasing the zinc concentrations in 25% of the transgenic lines generated, it also resulted in a decrease in plant and tuber size and overall yield due to what appears to be zinc deficiency in the aerial parts of the plant.
Plant Molecular Biology, 2004
The capacity to integrate transgenes into the tropical root crop cassava (Manihot esculenta Crant... more The capacity to integrate transgenes into the tropical root crop cassava (Manihot esculenta Crantz) is now established and being utilized to generate plants expressing traits of agronomic interest. The tissue culture and gene transfer systems currently employed to produce these transgenic cassava have improved significantly over the past 5 years and are assessed and compared in this review. Programs are underway to develop cassava with enhanced resistance to viral diseases and insects pests, improved nutritional content, modified and increased starch metabolism and reduced cyanogenic content of processed roots. Each of these is described individually for the underlying biology the molecular strategies being employed and progress achieved towards the desired product. Important advances have occurred, with transgenic plants from several laboratories being prepared for field trails.
Euphytica, 1996
Tartary buckwheat (Fagopyrum tataricum) was successfully hybridized with common buckwheat (F escu... more Tartary buckwheat (Fagopyrum tataricum) was successfully hybridized with common buckwheat (F esculentum), both diploid (2n = 16), using the latter as male parent during bud pollination. The barrier normally encountered in such hybridization was overcome by enhancing the cross-compatibility of the two species, which was accomplished by synthesizing a unique genotype of common buckwheat. This novel plant was produced by selecting common buckwheat plants that exhibited, at isozyme loci PGM, SKDH and ADH, alleles with similar mobility to those found in tartary and then transferring these alleles to a single plant through six generations of breeding. Ovule culture was used to rescue the 7-10 day old embryos. On the rescue-culture medium 41% of the hybrid embryos formed calli larger than 200 pm in diameter. Most ceased to grow before reaching 1500 µm, but four out of 263 cultured ovules continued to grow as callus. One of these differentiated and formed callus with buds and shoots from which cloned plants were produced. The remaining embryos either did not grow at all or formed very small calli. When tartary was crossed with the original genotype of common buckwheat, only 22% of the hybrid embryos formed small calli and none differentiated. Hybridity of the calli and the plantlets was determined by RAPD and isozyme analysis, respectively. Flowers produced by the hybrid plants were of the same type (homomorphic) and size as those of tartary, but with white sepals like common buckwheat .
African Journal of …, 2010
Cassava (Manihot esculenta) is the most important root crop in the tropics and due to its drought... more Cassava (Manihot esculenta) is the most important root crop in the tropics and due to its drought tolerance, ability to grow in poor soils, and resistance to herbivore, cassava is well suited for cultivation by subsistence farmers. However, its use and expansion is constrained by ...
Annual Review of Plant Biology, 2011
More than 250 million Africans rely on the starchy root crop cassava (Manihot esculenta) as their... more More than 250 million Africans rely on the starchy root crop cassava (Manihot esculenta) as their staple source of calories. A typical cassava-based diet, however, provides less than 30% of the minimum daily requirement for protein and only 10%–20% of that for iron, zinc, and vitamin A. The BioCassava Plus (BC+) program has employed modern biotechnologies intended to improve the health of Africans through the development and delivery of genetically engineered cassava with increased nutrient (zinc, iron, protein, and vitamin A) levels. Additional traits addressed by BioCassava Plus include increased shelf life, reductions in toxic cyanogenic glycosides to safe levels, and resistance to viral disease. The program also provides incentives for the adoption of biofortified cassava. Proof of concept was achieved for each of the target traits. Results from field trials in Puerto Rico, the first confined field trials in Nigeria to use genetically engineered organisms, and ex ante impact ana...
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Papers by Dimuth Siritunga