Simultaneous expression of Arabidopsis ρ-hydroxyphenylpyruvate dioxygenase and MPBQ methyltransferase in transgenic corn kernels triples the tocopherol content
ABSTRACT The quantity and composition of tocopherols (compounds with vitamin E activity) vary widely among different plant species reflecting the expression, activity and substrate specificity of enzymes in the corresponding metabolic pathway. Two Arabidopsis cDNA clones corresponding to ρ-hydroxyphenylpyruvate dioxygenase (HPPD) and 2-methyl-6-phytylplastoquinol methyltransferase (MPBQ MT) were constitutively expressed in corn to further characterize the pathway and increase the kernel tocopherol content. Transgenic kernels contained up to 3 times as much γ-tocopherol as their wild type counterparts whereas other tocopherol isomers remained undetectable. Biofortification by metabolic engineering offers a sustainable alternative to vitamin E supplementation for the improvement of human health.
Full-textDOI: · Available from: Changfu Zhu, Mar 24, 2015
- SourceAvailable from: Ludovic Bassie
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- "The combined expression of HPPD and MPBQ-MT resulted in a threefold increase in c-tocopherol levels without changing the total tocopherol content (Naqvi et al., 2011b). These experiments again showed that flux was directed into the a-branch but in this case it was blocked by low c–TMT activity, forcing the accumulation of c–tocopherol (Naqvi et al., 2011b). "
ABSTRACT: Antioxidants are protective molecules that neutralize reactive oxygen species and prevent oxidative damage to cellular components such as membranes, proteins and nucleic acids, therefore reducing the rate of cell death and hence the effects of ageing and ageing-related diseases. The fortification of food with antioxidants represents an overlap between two diverse environments, namely fortification of staple foods with essential nutrients that happen to have antioxidant properties (e.g. vitamins C and E) and the fortification of luxury foods with health-promoting but non-essential antioxidants such as flavonoids as part of the nutraceuticals/functional foods industry. Although processed foods can be artificially fortified with vitamins, minerals and nutraceuticals, a more sustainable approach is to introduce the traits for such health-promoting compounds at source, an approach known as biofortification. Regardless of the target compound, the same challenges arise when considering the biofortification of plants with antioxidants, that is the need to modulate endogenous metabolic pathways to increase the production of specific antioxidants without affecting plant growth and development and without collateral effects on other metabolic pathways. These challenges become even more intricate as we move from the engineering of individual pathways to several pathways simultaneously. In this review, we consider the state of the art in antioxidant biofortification and discuss the challenges that remain to be overcome in the development of nutritionally complete and health-promoting functional foods.Plant Biotechnology Journal 09/2012; 11(2). DOI:10.1111/j.1467-7652.2012.00740.x · 5.68 Impact Factor
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- "Similarly, Tavya et al. (2007) reported a 10.4- fold increase in a-tocopherol levels and a 14.9-fold increase in b-tocopherol levels in soybean seeds expressing Perilla frutescens c-TMT. The constitutive expression of two Arabidopsis cDNA clones encoding q-hydroxyphenylpyruvate dioxygenase (HPPD) and 2-methyl-6-phytyl- plastoquinol methyltransferase (MPBQ MT) increased the tocopherol content by threefold in transgenic maize (Naqvi et al. 2011). Overexpression of Arabidopsis HPPD in rice grains shifted tocopherol synthesis from the c to the a form with no increase in absolute tocopherol levels (Farré et al. in press). "
ABSTRACT: Malnutrition is a prevalent and entrenched global socioeconomic challenge that reflects the combined impact of poverty, poor access to food, inefficient food distribution infrastructure, and an over-reliance on subsistence mono-agriculture. The dependence on staple cereals lacking many essential nutrients means that malnutrition is endemic in developing countries. Most individuals lack diverse diets and are therefore exposed to nutrient deficiencies. Plant biotechnology could play a major role in combating malnutrition through the engineering of nutritionally enhanced crops. In this article, we discuss different approaches that can enhance the nutritional content of staple crops by genetic engineering (GE) as well as the functionality and safety assessments required before nutritionally enhanced GE crops can be deployed in the field. We also consider major constraints that hinder the adoption of GE technology at different levels and suggest policies that could be adopted to accelerate the deployment of nutritionally enhanced GE crops within a multicomponent strategy to combat malnutrition.Genes & Nutrition 08/2012; 8(1). DOI:10.1007/s12263-012-0315-5 · 3.42 Impact Factor
Article: Rethinking metabolic control[Show abstract] [Hide abstract]
ABSTRACT: Modulation of metabolic fluxes in plants is usually not a successful business. The main reason is our limited understanding of metabolic plasticity and metabolic control, with the latter still largely influenced by the idea that each pathway has a rate limiting step controlling the flux. Not only is experimental evidence for such steps lacking for most pathways, despite intensive search, but there are also theoretical arguments against the idea that highly regulated enzymes catalyzing reactions far from equilibrium must be considered a priori rate limiting. Conversely, it is argued that reactions close to equilibrium need a lot of enzyme to be maintained close to equilibrium and, contrary to accepted wisdom, begin to limit flux when reduced. Using a few key examples of plant metabolic pathways as case studies, I draw some general conclusions. The approach of augmenting flux by pushing a pathway from above is well exemplified by the attempts at increasing starch content in potato tubers, where several different approaches failed. Also pulling at the other end (close to the end product) has yielded little improvement, while targeting a reaction close to equilibrium (ADP/ATP translocation at the plastid envelope) successfully increased starch content. Rethinking control is equally well applicable to photosynthesis, with prime examples of ‘neglected’, unregulated enzymes exerting significant control and overprized ‘limiting’ enzymes having little control in normal conditions like rubisco.In this new paradigm, the role of most control mechanisms is also challenged: feedback inhibition and post-translational modification of enzymes are relevant to metabolite homeostasis rather than flux control, with moiety conservation being a major reason for this constraint. I advocate a more extensive use of control circuitry elements (e.g. sensors like riboswitches), metabolic shortcuts and transcription factors in metabolic engineering.Plant Science 04/2009; 176(4-176):441-451. DOI:10.1016/j.plantsci.2009.01.005 · 4.11 Impact Factor