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

ABSTRACT: In this study, β-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-β-carotene, the most nutritionally efficacious carotenoid. β-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 β-carotene enhanced storage roots. Most significantly, an inverse correlation was observed between β-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 β-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.

ORGANISM(S): Manihot esculenta

PROVIDER: GSE100319 | GEO | 2017/06/22

SECONDARY ACCESSION(S): PRJNA391307

REPOSITORIES: GEO

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Project description:Cotton (Gossypium hirsutum L) is an important crop world wide that provides fiber for the textile industry. Cotton is a perennial plant that stores starch in stems and roots to provide carbohydrates for growth in subsequent seasons. These reserves are not available to produce seed and fiber when cotton is usually grown as an annual crop. Analysis of developing cotton plants indicated that starch levels peaked about the time of first anthesis then began to decline. An earlier peak of levels of starch was occasionally observed and in some greenhouse-grown samples starch increased 2 week after first bloom. Microarray analyses compared gene expression in tissues containing low levels of starch with tissues rapidly accumulating starch. Statistical analysis of differentially expressed genes indicated increased expression among genes associated with carbohydrate metabolism, transcription activity and the proteasome. Genes associated with starch synthesis, starch degradation, sucrose metabolism, hexose metabolism, raffinose synthesis and trehalose synthesis increased in expression in starch accumulating tissues. The anticipated changes in these sugars were largely confirmed by measuring soluble sugars in relevant tissues. We propose that altering expressions of genes and pathways identified in this work could be used to more efficiently mobilize stored carbohydrate to fiber production. Keywords: starch accumulating, stem, root Genes expression was compared between cotton stems that were low in starch and accumulating starch. Gene expression was also compared between cotton roots that were low in starch and accumulating starch. A total of three microarrays were used. One dye swap was used. Material from the field were harvested 2 weeks apart. Greenhouse grown material were planted at two week intervals and harvested at the same time. NOTE that the channel representing the low starch material only gave about half of the total signal than the high starch samples. QPCR of 9 genes confirmed differential expression of 8 of them. QPCR also confirmed similar expression of two genes not predicted to be differentially expressed by the microarray analysis. Therefore no correction was made for the apparent difference in the hybridization of high and low starch samples.

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

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