From in planta Function to Vitamin-Rich Food Crops: The ACE of Biofortification

Abstract

Humans are highly dependent on plants to reach their dietary requirements, as plant products contribute both to energy and essential nutrients. For many decades, plant breeders have been able to gradually increase yields of several staple crops, thereby alleviating nutritional needs with varying degrees of success. However, many staple crops such as rice, wheat and corn, although delivering sufficient calories, fail to satisfy micronutrient demands, causing the so called ‘hidden hunger.’ Biofortification, the process of augmenting nutritional quality of food through the use of agricultural methodologies, is a pivotal asset in the fight against micronutrient malnutrition, mainly due to vitamin and mineral deficiencies. Several technical advances have led to recent breakthroughs. Nutritional genomics has come to fruition based on marker-assisted breeding enabling rapid identification of micronutrient related quantitative trait loci (QTL) in the germplasm of interest. As a complement to these breeding techniques, metabolic engineering approaches, relying on a continuously growing fundamental knowledge of plant metabolism, are able to overcome some of the inevitable pitfalls of breeding. Alteration of micronutrient levels does also require fundamental knowledge about their role and influence on plant growth and development. This review focuses on our knowledge about provitamin A (beta-carotene), vitamin C (ascorbate) and the vitamin E group (tocochromanols). We begin by providing an overview of the functions of these vitamins in planta, followed by highlighting some of the achievements in the nutritional enhancement of food crops via conventional breeding and genetic modification, concluding with an evaluation of the need for such biofortification interventions. The review further elaborates on the vast potential of creating nutritionally enhanced crops through multi-pathway engineering and the synergistic potential of conventional breeding in combination with genetic engineering, including the impact of novel genome editing technologies.

Metabolic engineering of rice endosperm towards higher vitamin B1 accumulation

“…To avoid detrimental side‐effects on plant physiology (Bocobza et al ., 2013; Wang et al ., 2016), biofortification approaches are preferentially limited to the tissue of interest (Strobbe et al ., 2018; Strobbe and Van Der Straeten, 2018), in the case of rice being the consumed starchy endosperm. To achieve enhanced accumulation of thiamin in polished white rice, we aimed at endosperm‐specific enhancement of thiamin biosynthesis.…”

The coenzyme thiamine diphosphate displays a daily rhythm in the Arabidopsis nucleus

“…In particular, the thiamine dosage response data show that core biochemical pathways are affected and more specifically the level of certain photosynthetic pigments can be correlated with thiamine supply. Often referred to as the "energy vitamin" 41 , TDP drives the activity of pyruvate dehydrogenase (glycolysis), pyruvate decarboxylase (glycolysis), α-ketoglutarate dehydrogenase (TCA cycle) and transketolase (oxidative pentose phosphate pathway) in all organisms. Notably, the latter enzyme is also involved in the Calvin cycle, responsible for CO 2 fixation in plants.…”

Plant Synthetic Metabolic Engineering for Enhancing Crop Nutritional Quality

“…Human cannot synthesize these compounds, thus must obtain them from the diet, especially from plant foods ( Garcia-Casal et al., 2017 ). However, as the main dietary components for human population, the most consumed stable crops and many edible plants deliver inadequate amounts of these micronutrients ( Strobbe et al., 2018 ). Biofortification via genetic engineering provides a crucial tool to enrich crop vitamins in the fight against micronutrient malnutrition.…”

“…Similarly, overexpressing the PDX gene (encoding a pyridoxal phosphate synthase, a key enzyme of vitamin B6 biosynthesis) also could significantly increase the content of vitamin B6 in cassava ( Chen and Xiong, 2009 , Li et al., 2015 ). In addition, using a similar strategy expressing one or more key enzyme genes involved in vitamin C or E biosynthesis, vitamin C biofortification was achieved in tomato, potato, and maize ( Naqvi et al., 2009 , Qin et al., 2011 , Bulley et al., 2012 ), and vitamin E content was enhanced in rice, maize, and barley ( Babura et al., 2017 , Chen et al., 2017 , Strobbe et al., 2018 ).…”