Plant compounds that are perceived by humans to have color are generally referred to as 'pigments'. Their varied structures and colors have long fascinated chemists and biologists, who have examined their chemical and physical properties, their mode of synthesis, and their physiological and ecological roles. Plant pigments also have a long history of use by humans. The major classes of plant pigments, with the exception of the chlorophylls, are reviewed here. Anthocyanins, a class of flavonoids derived ultimately from phenylalanine, are water-soluble, synthesized in the cytosol, and localized in vacuoles. They provide a wide range of colors ranging from orange/red to violet/blue. In addition to various modifications to their structures, their specific color also depends on co-pigments, metal ions and pH. They are widely distributed in the plant kingdom. The lipid-soluble, yellow-to-red carotenoids, a subclass of terpenoids, are also distributed ubiquitously in plants. They are synthesized in chloroplasts and are essential to the integrity of the photosynthetic apparatus. Betalains, also conferring yellow-to-red colors, are nitrogen-containing water-soluble compounds derived from tyrosine that are found only in a limited number of plant lineages. In contrast to anthocyanins and carotenoids, the biosynthetic pathway of betalains is only partially understood. All three classes of pigments act as visible signals to attract insects, birds and animals for pollination and seed dispersal. They also protect plants from damage caused by UV and visible light.

https://onlinelibrary.wiley.com/doi/epdf/10.1111/j.1365-313X.2008.03447.x

Biosynthesis of plant pigments: anthocyanins, betalains and carotenoids

Food and Agricultural Organization of the United Nations PA N I S F I A T G u id e in e s o n fo o d fo r tific atio n w th m ic r o n u tr ie n ts Interest in micronutrient malnutrition has increased greatly over the last few years. One of the main reasons is the realization that micronutrient malnutrition contributes substantially to the global burden of disease. Furthermore, although micronutrient malnutrition is more frequent and severe in the developing world and among disadvantaged populations, it also represents a public health problem in some industrialized countries. Measures to correct micronutrient deficiencies aim at ensuring consumption of a balanced diet that is adequate in every nutrient. Unfortunately, this is far from being achieved everywhere since it requires universal access to adequate food and appropriate dietary habits. Food fortification has the dual advantage of being able to deliver nutrients to large segments of the population without requiring radical changes in food consumption patterns.

Guidelines on food fortification with micronutrients

Chapter 1: Overview of Zinc Nutrition ............................................................................................................... S99 1.1 Biological functions of zinc ............................................................................................................................. S99 1.2 Tissue zinc distribution and reserves .............................................................................................................. S99 1.3 Zinc metabolism ........................................................................................................................................... S100 1.4 Importance of zinc for human health........................................................................................................... S101 1.5 Human zinc requirements............................................................................................................................. S105 1.5.1 Adult men ............................................................................................................................................. S106 1.5.2 Adult women......................................................................................................................................... S109 1.5.3 Children ................................................................................................................................................ S110 1.5.4 Pregnancy.............................................................................................................................................. S111 1.5.5 Lactation ............................................................................................................................................... S112 1.6 Dietary sources of zinc and suggested revisions of Recommended Daily Intakes .................................... S112 1.6.1 Dietary sources of zinc and factors affecting the proportion of zinc available for absorption ........ S112 1.6.2 Revised estimates of dietary requirements and recommended intakes for zinc ............................... S114 1.7 Zinc toxicity.................................................................................................................................................... S118 1.8 Causes of zinc deficiency and groups at high risk ....................................................................................... S121 1.9 Summary ........................................................................................................................................................ S123

International Zinc Nutrition Consultative Group (IZiNCG) technical document #1. Assessment of the risk of zinc deficiency in populations and options for its control.

The biosynthesis and nutritional uses of carotenoids.

"Golden Rice" is a variety of rice engineered to produce beta-carotene (pro-vitamin A) to help combat vitamin A deficiency, and it has been predicted that its contribution to alleviating vitamin A deficiency would be substantially improved through even higher beta-carotene content. We hypothesized that the daffodil gene encoding phytoene synthase (psy), one of the two genes used to develop Golden Rice, was the limiting step in beta-carotene accumulation. Through systematic testing of other plant psys, we identified a psy from maize that substantially increased carotenoid accumulation in a model plant system. We went on to develop "Golden Rice 2" introducing this psy in combination with the Erwinia uredovora carotene desaturase (crtI) used to generate the original Golden Rice. We observed an increase in total carotenoids of up to 23-fold (maximum 37 microg/g) compared to the original Golden Rice and a preferential accumulation of beta-carotene.

/pdf/improving-the-nutritional-value-of-golden-rice-through-10dtf5qb9i.pdf

Improving the nutritional value of Golden Rice through increased pro-vitamin A content

Rice (Oryza sativa), a major staple food, is usually milled to remove the oil-rich aleurone layer that turns rancid upon storage, especially in tropical areas. The remaining edible part of rice grains, the endosperm, lacks several essential nutrients, such as provitamin A. Thus, predominant rice consumption promotes vitamin A deficiency, a serious public health problem in at least 26 countries, including highly populated areas of Asia, Africa, and Latin America. Recombinant DNA technology was used to improve its nutritional value in this respect. A combination of transgenes enabled biosynthesis of provitamin A in the endosperm.

https://science.sciencemag.org/content/sci/287/5451/303.full.pdf

Engineering the Provitamin A (β-Carotene) Biosynthetic Pathway into (Carotenoid-Free) Rice Endosperm

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.

/pdf/golden-rice-introducing-the-b-carotene-biosynthesis-pathway-556b8u59bv.pdf

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

To obtain a functioning provitamin A (beta-carotene) biosynthetic pathway in rice endosperm, we introduced in a single, combined transformation effort the cDNAs coding for (1) phytoene synthase (psy) and (2) lycopene beta-cyclase (beta-lcy; both from Narcissus pseudonarcissus and both under control of the endosperm-specific glutelin promoter), with (3) a bacterial phytoene desaturase (crtI, from Erwinia uredovora under constitutive 35S promoter control). This combination covers the requirements for beta-carotene synthesis, and yellow, beta-carotene-bearing rice endosperm was obtained in the T0 generation. However, further experiments revealed that the presence of beta-lcy was not necessary, since psy and crtI alone were able to drive beta-carotene synthesis as well as the formation of further downstream xanthophylls. This finding could be explained if these downstream enzymes are either constitutively expressed in rice endosperm or are induced by the transformation, e.g. by products derived therefrom. Based on results in N. pseudonarcissus as a model system, a likely hypothesis can be developed that trans lycopene or a trans lycopene derivative acts as an inductor in a kind of feedback mechanism stimulating endogenous carotenogenic genes.

Biosynthesis of β‐Carotene (Provitamin a) in Rice Endosperm Achieved by Genetic Engineering

Cre-mediated autoexcision of selectable marker genes in soybean, cotton, canola and maize transgenic plants

Transgenic plant production in monocotyledonous species has primarily relied on embryogenic callus induction from both immature and mature embryos as the pathway for plant regeneration. We have efficiently regenerated fertile transgenic wheat plants through organogenesis after Agrobacterium-mediated direct transformation of mechanically isolated mature embryos from field-grown seed. Centrifugation of the mature embryos in the presence of Agrobacterium was found to be essential for efficient T-DNA delivery to the relevant regenerable cells. The inoculated mature embryos formed multiple buds/shoots on high-cytokinin medium, which directly regenerated into transgenic shoots on hormone-free medium containing glyphosate for selection. Rooted transgenic plantlets were obtained within 10-12 weeks after inoculation. Further optimization of this transformation protocol resulted in significant reduction of chimeric plants to below 5%, as indicated by leaf GUS staining and T1 transgene segregation analysis. Direct transformation of wheat mature embryos has substantial advantages over traditional immature embryo-based transformation systems, including long-term storability of the mature dry explants, scalability, and greatly improved flexibility and consistency in transformation experiments.

/pdf/agrobacterium-mediated-direct-transformation-of-wheat-mature-1bd9l8ch.pdf

Xudong Ye

Papers

Engineering the Provitamin A (β-Carotene) Biosynthetic Pathway into (Carotenoid-Free) Rice Endosperm

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

Biosynthesis of β‐Carotene (Provitamin a) in Rice Endosperm Achieved by Genetic Engineering

Cre-mediated autoexcision of selectable marker genes in soybean, cotton, canola and maize transgenic plants

Agrobacterium-mediated direct transformation of wheat mature embryos through organogenesis