Golden Rice: Introducing the β-Carotene Biosynthesis Pathway into Rice Endosperm by Genetic Engineering to Defeat Vitamin A Deficiency

Abstract

To obtain a functioning provitamin A (beta-carotene) biosynthetic pathway in rice endosperm, we introduced in a single, combined transformation effort the cDNA coding for phytoene synthase (psy) and lycopene beta-cyclase (beta-lcy) both from Narcissus pseudonarcissus and both under the control of the endosperm-specific glutelin promoter together with a bacterial phytoene desaturase (crtI, from Erwinia uredovora under constitutive 35S promoter control). This combination covers the requirements for beta-carotene synthesis and, as hoped, yellow beta-carotene-bearing rice endosperm was obtained in the T(0)-generation. Additional experiments revealed that the presence of beta-lcy was not necessary, because psy and crtI alone were able to drive beta-carotene synthesis as well as the formation of further downstream xanthophylls. Plausible explanations for this finding are that these downstream enzymes are constitutively expressed in rice endosperm or are induced by the transformation, e.g., by enzymatically formed products. Results using N. pseudonarcissus as a model system led to the development of a hypothesis, our present working model, that trans-lycopene or a trans-lycopene derivative acts as an inductor in a kind of feedback mechanism stimulating endogenous carotenogenic genes. Various institutional arrangements for disseminating Golden Rice to research institutes in developing countries also are discussed.

Carotenoids in nature: insights from plants and beyond

“…Carotenoid accumulation has been achieved in oil seeds of canola (Brassica napus) through the overexpression of PSY, which resulted in 43-50-fold increase in total seed carotenoid content (Shewmaker et al 1999;Lindgren et al 2003). 'Golden rice 2' is a high b-carotene accumulating line overexpressing PSY from maize as well as bacterial CrtI (from Erwinia uredovora) and accumulates 23-fold more carotenoids (37 mg g -1 ) than was the case for the initial 'golden rice', which overexpressed PSY from daffodil (Beyer et al 2002;Paine et al 2005). Underground food crops, such as potato and carrot have also been engineered to have increased carotenoid content, in particular b-carotene and ketocarotenoids (e.g.…”

“…Several genes encoding enzymes in isoprenoid and carotenoid biosynthesis are the subject of negative and positive feedback regulatory processes and are likely to be mediated by a carotenoid or a molecule derived from a carotenoid (Römer et al 2000;Beyer et al 2002;Cuttriss et al 2007;Qin et al 2007;Bai et al 2009). There is strong evidence to show carotenoid metabolite feedback regulation requires post-transcriptional and transcriptional processes to modulate target genes that (1) supply isoprenoid precursors for carotenogenesis, (2) control activity of the ratelimiting phytoene synthase step and (3) control carotenoid flux through the branch to synthesis of a-and b-carotenes.…”

Genome Editing with Engineered Nucleases in Economically Important Animals and Plants: State of the Art in the Research Pipeline

“…Examples of the transgenic approach include Golden rice with provitamin A content (Beyer et al, 2002) or soybean with decreased α-linolenic fatty acid content (Flores et al, 2008). Seed oil composition in soybean was also the subject in the study by Haun et al (2014) who have used TALENs to knock-out the fatty acid desaturase 2 (fad2) genes.…”

Genetically Modified Rice with Health Benefits as a Means to Reduce Micronutrient Malnutrition

“…First of all, there are several studies in international peer-reviewed journals which report the reconstitution of the folate 79, 86, 88 and carotenoid biosynthetic pathway 75,91,92 . Second, while rice with a higher folate content, developed by metabolic engineering, is currently the most advanced folate enriched staple crop 89,93 , Golden Rice is the most advanced GM biofortified crop and will be most likely the first to be commercialized (An overview of the typical steps in the development process of transgenic biofortified crops, e.g.…”