Iron Biofortification of Staple Crops: Lessons and Challenges in Plant Genetics

Abstract

Plants are the ultimate source of iron in our diet, either directly as staple crops and vegetables or indirectly via animal fodder. Increasing the iron concentration of edible parts of plants, known as biofortification, is seen as a sustainable approach to alleviate iron deficiency which is a major global health issue. Advances in sequencing and gene technology are accelerating both forward and reverse genetic approaches. In this review, we summarize recent progress in iron biofortification using conventional plant breeding or transgenics. Interestingly, some of the gene targets already used for transgenic approaches are also identified as genetic factors for high iron in genome-wide association studies. Several quantitative trait loci and transgenes increase both iron and zinc, due to overlap in transporters and chelators for these two mineral micronutrients. Research efforts are predominantly aimed at increasing the total concentration of iron but enhancing its bioavailability is also addressed. In particular, increased biosynthesis of the metal chelator nicotianamine increases iron and zinc levels and improves bioavailability. The achievements to date are very promising in being able to provide sufficient iron in diets with less reliance on meat to feed a growing world population.

Seed Mineral Composition and Protein Content of Faba Beans (Vicia faba L.) with Contrasting Tannin Contents

“…The content of mineral elements such as Zn, Fe, and Se in seeds is affected by both permanent and variable soil environmental factors, and the larger variation due to G × E interactions when compared with the protein content, for example, indicates that the inheritance of these traits may be more complex. However, multi-environment data for several crop species, including pulses, have identified genotypes with high and stable trait expression in the presence of high G × E interactions [10]. The seed mineral concentration is shown to be a quantitative trait in seeds of legume species.…”

“…Mineral malnutrition affects millions of people globally, and is one of the most serious challenges to humankind (WHO, https://www.who.int/news-room/fact-sheets/detail/malnutrition). To address the mineral deficiencies in human populations, genetic biofortification through plant breeding has become an Agronomy 2020, 10, 511 2 of 10 option as a sustainable, cost-effective, and long-term approach for improving the amount of essential mineral elements in agricultural products [8][9][10]. This technique involves screening and developing micronutrient-rich germplasm, conducting genetic studies (including magnitude of stability through genotype × environment studies, trait heritability, and associations with important agronomic traits), and developing molecular markers to facilitate breeding [11].…”

Mineral Element Composition in Grain of Awned and Awnletted Wheat (Triticum aestivum L.) Cultivars: Tissue-Specific Iron Speciation and Phytate and Non-Phytate Ligand Ratio

“…Agronomic approaches have been efficient when (i) the soil contains insufficient amounts of certain element(s), which can be added to the agricultural system as fertilizers or (ii) when changes to phytoavailability of elements in the rhizosphere are required and pH-related intervention can offer solutions. On the other hand, variability in the elemental composition of the edible produce can be exploited to (i) introduce cultivars with superior mineral-use efficiency, provided there is no penalty to agronomically important traits or (ii) to identify candidate genes for future genetic optimisation [9]. After these interventions are implemented and a produce with the largest possible inherent concentration is available, the Fe status of the individual and other food components (e.g., dietary fibre, organic acids) will still play crucial roles in the availability of a certain element, with Fe being particularly problematic [34], further complicating the efforts to ensure optimal nutrition in humans.…”

“…Of the seven mineral elements often lacking in our diets, Fe deficiency is most widespread, affecting up to 60% of the global population [7]. However, increasing bio-available Fe concentration through the agronomic and genetic approaches in crops is challenging [9] for several reasons: (i) poor Fe availability in the soils limits uptake into plant roots [10], (ii) strict metabolic control over Fe accumulation and sequestration in plants tissues (sufficiency ranging between 50 and 150 mg Fe•kg −1 dry weight in leaves of crop plants [11]), (iii) removal of Fe-rich layers during the processing of staple grain [12], and (iv) poor Fe bioavailability from phytate-rich produce such as cereal grain [13].…”

Gene Expression Pattern of Vacuolar-Iron Transporter-Like (VTL) Genes in Hexaploid Wheat during Metal Stress

“…Most of these gene families are highly upregulated in roots subjected to Fe starvation conditions [24,25]. These works identify some of the important candidate genes as an important resource to strategize approaches for micronutrient biofortification in wheat [26].…”