Identification of nutrient and physical seed trait QTL in the model legume Lotus japonicus

Nutritional and genetic variation in a core set of Ethiopian Tef (Eragrostis tef) varieties

BACKGROUND

Tef (Eragrostis tef) is a tropical cereal domesticated and grown in the Ethiopian highlands, where it has been a staple food of Ethiopians for many centuries. Food insecurity and nutrient deficiencies are major problems in the country, so breeding for enhanced nutritional traits, such as Zn content, could help to alleviate problems with malnutrition.

RESULTS

To understand the breeding potential of nutritional traits in tef a core set of 24 varieties were sequenced and their mineral content, levels of phytate and protein, as well as a number of nutritionally valuable phenolic compounds measured in grain. Significant variation in all these traits was found between varieties. Genome wide sequencing of the 24 tef varieties revealed 3,193,582 unique SNPs and 897,272 unique INDELs relative to the tef reference var. Dabbi. Sequence analysis of two key transporter families involved in the uptake and transport of Zn by the plant led to the identification of 32 Zinc Iron Permease (ZIP) transporters and 14 Heavy Metal Associated (HMA) transporters in tef. Further analysis identified numerous variants, of which 14.6% of EtZIP and 12.4% of EtHMA variants were non-synonymous changes. Analysis of a key enzyme in flavanol synthesis, flavonoid 3'-hydroxylase (F3'H), identified a T-G variant in the tef homologue Et_s3159-0.29-1.mrna1 that was associated with the differences observed in kaempferol glycoside and quercetin glycoside levels.

CONCLUSION

Wide genetic and phenotypic variation was found in 24 Ethiopian tef varieties which would allow for breeding gains in many nutritional traits of importance to human health.

Molecular Mechanisms and Biochemical Pathways for Micronutrient Acquisition and Storage in Legumes to Support Biofortification for Nutritional Security

The world faces a grave situation of nutrient deficiency as a consequence of increased uptake of calorie-rich food that threaten nutritional security. More than half the world's population is affected by different forms of malnutrition. Unhealthy diets associated with poor nutrition carry a significant risk of developing non-communicable diseases, leading to a high mortality rate. Although considerable efforts have been made in agriculture to increase nutrient content in cereals, the successes are insufficient. The number of people affected by different forms of malnutrition has not decreased much in the recent past. While legumes are an integral part of the food system and widely grown in sub-Saharan Africa and South Asia, only limited efforts have been made to increase their nutrient content in these regions. Genetic variation for a majority of nutritional traits that ensure nutritional security in adverse conditions exists in the germplasm pool of legume crops. This diversity can be utilized by selective breeding for increased nutrients in seeds. The targeted identification of precise factors related to nutritional traits and their utilization in a breeding program can help mitigate malnutrition. The principal objective of this review is to present the molecular mechanisms of nutrient acquisition, transport and metabolism to support a biofortification strategy in legume crops to contribute to addressing malnutrition.

The maize shoot ionome: Its interaction partners, predictive power, and genetic determinants

An improved understanding of how to manipulate the accumulation and enrichment of mineral elements in aboveground plant tissues holds promise for future resource efficient and sustainable crop production. The objectives of this study were to (a) evaluate the influence of Fe regimes on mineral element concentrations and contents in the maize shoot as well as their correlations, (b) examine the predictive ability of physiological and morphological traits of individual genotypes of the IBM population from the concentration of mineral elements, and (c) identify genetic factors influencing the mineral element composition within and across Fe regimes. We evaluated the concentration and content of 12 mineral elements in shoots of the IBM population grown in sufficient and deficient Fe regimes and found for almost all mineral elements a significant (α = 0.05) genotypic variance. Across all mineral elements, the variance of genotype*Fe regime interactions was on average even more pronounced. High prediction abilities indicated that mineral elements are powerful predictors of morphological and physiological traits. Furthermore, our results suggest that ZmHMA2/3 and ZmMOT1 are major players in the natural genetic variation of Cd and Mo concentrations and contents of maize shoots, respectively.

Genome-wide association studies of Ca and Mn in the seeds of the common bean (Phaseolus vulgaris L.)

SNP markers linked to genes controlling Ca and Mn uptake were identified in the common bean seeds using DArT-based association mapping (AM). The Ca concentration in the seeds varied between 475 and 3,100 mg kg^-1 with an average of 1,280.9 mg kg^-1 and the Mn concentration ranged from 4.87 to 27.54 mg kg^-1 with a mean of 11.76 mg kg^-1. A total of 19,204 SNP markers were distributed across 11 chromosomes that correspond to the haploid genome number of the common bean. The highest value of ΔK was determined as K = 2, and 173 common bean genotypes were split into two main subclusters as POP1 (Mesoamerican) and POP2 (Andean). The results of the UPGMA dendrogram and PCA confirmed those of STRUCTURE analysis. MLM based on the Q + K model identified a large number of markers-trait associations. Of the 19,204 SNPs, five (on Pv2, 3, 8, 10 and 11) and four (on Pv2, 3, 8 and 11) SNPs were detected to be significantly related to the Ca content of the beans grown in Bornova and Menemen, respectively in 2015. In 2016, six SNPs (on Pv1-4, 8 and 10) were identified to be significantly associated with the Ca content of the seeds obtained from Bornova and six SNPs (on Pv1-4, 8 and 10) from Menemen. Eight (on Pv3, 5 and 11) and four (on Pv2, 5 and 11) SNPs had a significant association with Mn content in Bornova in 2015 and 2016, respectively. In Menemen, eight (on Pv3, 5, 8 and 11) and 11 (on Pv1, 2, 5, 10 and 11) SNPs had a significant correlation with Mn content in 2015 and 2016, respectively.

Genome-Wide SNP Identification and Association Mapping for Seed Mineral Concentration in Mung Bean (Vigna radiata L.)

Mung bean (Vigna radiata L.) quality is dependent on seed chemical composition, which in turn determines the benefits of its consumption for human health and nutrition. While mung bean is rich in a range of nutritional components, such as protein, carbohydrates and vitamins, it remains less well studied than other legume crops in terms of micronutrients. In addition, mung bean genomics and genetic resources are relatively sparse. The objectives of this research were three-fold, namely: to develop a genome-wide marker system for mung bean based on genotyping by sequencing (GBS), to evaluate diversity of mung beans available to breeders in the United States and finally, to perform a genome-wide association study (GWAS) for nutrient concentrations based on a seven mineral analysis using inductively coupled plasma (ICP) spectroscopy. All parts of our research were performed with 95 cultivated mung bean genotypes chosen from the USDA core collection representing accessions from 13 countries. Overall, we identified a total of 6,486 high quality single nucleotide polymorphisms (SNPs) from the GBS dataset and found 43 marker × trait associations (MTAs) with calcium, iron, potassium, manganese, phosphorous, sulfur or zinc concentrations in mung bean grain produced in either of two consecutive years' field experiments. The MTAs were scattered across 35 genomic regions explaining on average 22% of the variation for each seed nutrient in each year. Most of the gene regions provided valuable candidate loci to use in future breeding of new varieties of mung bean and further the understanding of genetic control of nutritional properties in the crop. Other SNPs identified in this study will serve as important resources to enable marker-assisted selection (MAS) for nutritional improvement in mung bean and to analyze cultivars of mung bean.

The first genetic map for yellow lupin enables genetic dissection of adaptation traits in an orphan grain legume crop

BACKGROUND

Yellow lupin (Lupinus luteus L.) is a promising grain legume for productive and sustainable crop rotations. It has the advantages of high tolerance to soil acidity and excellent seed quality, but its current yield potential is poor, especially in low rainfall environments. Key adaptation traits such as phenology and enhanced stress tolerance are often complex and controlled by several genes. Genomic-enabled technologies may help to improve our basic understanding of these traits and to provide selective markers in breeding. However, in yellow lupin there are very limited genomic resources to support research and no published information is available on the genetic control of adaptation traits.

RESULTS

We aimed to address these deficiencies by developing the first linkage map for yellow lupin and conducting quantitative trait locus (QTL) analysis of yield under well-watered (WW) and water-deficit (WT) conditions. Two next-generation sequencing marker approaches - genotyping-by-sequencing (GBS) and Diversity Array Technology (DArT) sequencing - were employed to genotype a recombinant inbred line (RIL) population developed from a bi-parental cross between wild and domesticated parents. A total of 2,458 filtered single nucleotide polymorphism (SNP) and presence / absence variation (PAV) markers were used to develop a genetic map comprising 40 linkage groups, the first reported for this species. A number of significant QTLs controlling total biomass and 100-seed weight under two water (WW and WD) regimes were found on linkage groups YL-03, YL-09 and YL-26 that together explained 9 and 28% of total phenotypic variability. QTLs associated with length of the reproductive phase and time to flower were found on YL-01, YL-21, YL-35 and YL-40 that together explained a total of 12 and 44% of total phenotypic variation.

CONCLUSION

These genomic resources and the QTL information offer significant potential for use in marker-assisted selection in yellow lupin.

Seed mineral reserves and vigour of Bambara groundnut (Vigna subterranea L.) landraces differing in seed coat colour

A newly emerged seedling, given light and water, but no external source of minerals, uses its internal mineral nutrient reserves effectively for an early establishment. This research sought to investigate the influence of seed coat colour on the abundance of mineral elements in Bambara groundnut. Four landraces (G340A, Kazai, Kazuma, and Mana) varying in seed coat colour were analysed for differences in seed mineral composition using energy dispersive x-ray (EDX) analysis and atomic absorption spectrometry (AAS). Seeds were germinated at 10 °C and 25 °C, and various indices including, (1) mean emergence time, (2) mean germination rate, (3) coefficient of velocity of germination, and (4) final germination percentage (FGP) were calculated. The importance of seed mineral elements in the establishment of Bambara groundnut was examined by measuring root length (RL), shoot length (SL), shoot dry mass (SDM), and root dry mass (RDM). Plant tissue elemental analysis was done using flame atomic emission spectrometry (FAES) for K and flame atomic absorption spectrometry (FAAS) for Mg, Cu, Mn, and Zn. There were significant differences (P < 0.001) in mineral element content of dry seeds. G340A and Kazai had the highest and the lowest K, P, Mg, Mn, and Zn (11.65 gkg^-1, 7.2 gkg^-1, 2.33 gkg^-1, 59.56 mgkg^-1, and 44.42 mgkg^-1), and (8.82 gkg^-1, 4.75 gkg^-1, 1.38 gkg^-1, 48.9 mgkg^-1, and 42.6 mgkg^-1), respectively. Cold test germination indices were significantly different, the highest FGP was 73.3% in G340A and the lowest was 57.8% in Kazai. There were strong positive correlations between seed mineral concentration and plant growth parameters (p < 0.001). We concluded that (1) seed mineral concentration has a significant impact on the early establishment of Bambara groundnut and (2) the dark-coloured landraces (hue 8º) used in this study have the highest concentration of macro and micro elements compared to light coloured seeds (hue 38º).

Legume biofortification is an underexploited strategy for combatting hidden hunger

Legumes are the world's primary source of dietary protein and are particularly important for those in developing economies. However, the biofortification potential of legumes remains underexploited. Legumes offer a diversity of micronutrients and amino acids, exceeding or complementing the profiles of cereals. As such, the enhancement of legume nutritional composition presents an appealing target for addressing the "hidden hunger" of global micronutrient malnutrition. Affecting ~2 billion people, micronutrient malnutrition causes severe health effects ranging from stunted growth to reduced lifespan. An increased availability of micronutrient-enriched legumes, particularly to those in socio-economically deprived areas, would serve the dual functions of ameliorating hidden hunger and increasing the positive health effects associated with legumes. Here, we give an updated overview of breeding approaches for the nutritional improvement of legumes, and crucially, we highlight the importance of considering nutritional improvement in a wider ecological context. Specifically, we review the potential of the legume microbiome for agronomic trait improvement and highlight the need for increased genetic, biochemical, and environmental data resources. Finally, we state that such resources should be complemented by an international and multidisciplinary initiative that will drive crop improvement and, most importantly, ensure that research outcomes benefit those who need them most.

QTL Mapping of Genome Regions Controlling Manganese Uptake in Lentil Seed

This study evaluated Mn concentration in the seeds of 120 RILs of lentil developed from the cross “CDC Redberry” × “ILL7502”. Micronutrient analysis using atomic absorption spectrometry indicated mean seed manganese (Mn) concentrations ranging from 8.5 to 26.8 mg/kg, based on replicated field trials grown at three locations in Turkey in 2012 and 2013. A linkage map of lentil was constructed and consisted of seven linkage groups with 5,385 DNA markers. The total map length was 973.1 cM, with an average distance between markers of 0.18 cM. A total of 6 QTL for Mn concentration were identified using composite interval mapping (CIM). All QTL were statistically significant and explained 15.3–24.1% of the phenotypic variation, with LOD scores ranging from 3.00 to 4.42. The high-density genetic map reported in this study will increase fundamental knowledge of the genome structure of lentil, and will be the basis for the development of micronutrient-enriched lentil genotypes to support biofortification efforts.

Genome-wide SNP identification, linkage map construction and QTL mapping for seed mineral concentrations and contents in pea (Pisum sativum L.)

BACKGROUND

Marker-assisted breeding is now routinely used in major crops to facilitate more efficient cultivar improvement. This has been significantly enabled by the use of next-generation sequencing technology to identify loci and markers associated with traits of interest. While rich in a range of nutritional components, such as protein, mineral nutrients, carbohydrates and several vitamins, pea (Pisum sativum L.), one of the oldest domesticated crops in the world, remains behind many other crops in the availability of genomic and genetic resources. To further improve mineral nutrient levels in pea seeds requires the development of genome-wide tools. The objectives of this research were to develop these tools by: identifying genome-wide single nucleotide polymorphisms (SNPs) using genotyping by sequencing (GBS); constructing a high-density linkage map and comparative maps with other legumes, and identifying quantitative trait loci (QTL) for levels of boron, calcium, iron, potassium, magnesium, manganese, molybdenum, phosphorous, sulfur, and zinc in the seed, as well as for seed weight.

RESULTS

In this study, 1609 high quality SNPs were found to be polymorphic between 'Kiflica' and 'Aragorn', two parents of an F6-derived recombinant inbred line (RIL) population. Mapping 1683 markers including 75 previously published markers and 1608 SNPs developed from the present study generated a linkage map of size 1310.1 cM. Comparative mapping with other legumes demonstrated that the highest level of synteny was observed between pea and the genome of Medicago truncatula. QTL analysis of the RIL population across two locations revealed at least one QTL for each of the mineral nutrient traits. In total, 46 seed mineral concentration QTLs, 37 seed mineral content QTLs, and 6 seed weight QTLs were discovered. The QTLs explained from 2.4% to 43.3% of the phenotypic variance.

CONCLUSION

The genome-wide SNPs and the genetic linkage map developed in this study permitted QTL identification for pea seed mineral nutrients that will serve as important resources to enable marker-assisted selection (MAS) for nutritional quality traits in pea breeding programs.

Genetic Dissection of ICP-Detected Nutrient Accumulation in the Whole Seed of Common Bean (Phaseolus vulgaris L.)

Nutrient transport to grain legume seeds is not well studied and can benefit from modern methods of elemental analysis including spectroscopic techniques. Some cations such as potassium (K) and magnesium (Mg) are needed for plant physiological purposes. Meanwhile, some minerals such as copper (Cu), iron (Fe), molybdenum (Mo), and zinc (Zn) are important micronutrients. Phosphorus (P) is rich in legumes, while sulfur (S) concentration is related to essential amino acids. In this research, the goal was to analyze a genetic mapping population of common bean (Phaseolus vulgaris L.) with inductively coupled plasma (ICP) spectrophotometry to determine concentrations of and to discover quantitative trait loci (QTL) for 15 elements in ground flour of whole seeds. The population was grown in randomized complete block design experiments that had been used before to analyze Fe and Zn. A total of 21 QTL were identified for nine additional elements, of which four QTL were found for Cu followed by three each for Mg, Mn, and P. Fewer QTL were found for K, Na and S. Boron (B) and calcium (Ca) had only one QTL each. The utility of the QTL for breeding adaptation to element deficient soils and association with previously discovered nutritional loci are discussed.

Evaluation of Minerals, Phytochemical Compounds and Antioxidant Activity of Mexican, Central American, and African Green Leafy Vegetables

The green leafy vegetables Cnidoscolus aconitifolius and Crotalaria longirostrata are native to Mexico and Central America, while Solanum scabrum and Gynandropsis gynandra are native to Africa. They are consumed in both rural and urban areas in those places as a main food, food ingredient or traditional medicine. Currently, there is limited information about their nutritional and phytochemical composition. Therefore, mineral, vitamin C, phenolic and flavonoid concentration, and antioxidant activity were evaluated in multiple accessions of these leafy vegetables, and their mineral and vitamin C contribution per serving was calculated. The concentrations of Ca, K, Mg and P in these leafy vegetables were 0.82-2.32, 1.61-7.29, 0.61-1.48 and 0.27-1.44 mg/g fresh weight (FW), respectively. The flavonoid concentration in S. scabrum accessions was up to 1413 μg catechin equivalents/g FW, while the highest antioxidant activities were obtained in C. longirostrata accessions (52-60 μmol Trolox equivalents/g FW). According to guidelines established by the US Food and Drug Administration, a serving size (30 g FW) of C. longirostrata would be considered an excellent source of Mo (20 % or more of the daily value), and a serving of any of these green leafy vegetables would be an excellent source of vitamin C. Considering the importance of the minerals, phytochemicals and antioxidants in human health and their presence in these indigenous green leafy vegetables, efforts to promote their consumption should be implemented.

Shoot ionome to predict the synergism and antagonism between nutrients as affected by substrate and physiological status

The elemental composition of a tissue or organism is defined as ionome. However, the combined effects on the shoot ionome determined by the taxonomic character, the nutrient status and different substrates have not been investigated. This study tests the hypothesis that phylogenetic variation of monocots and dicots grown in iron deficiency can be distinguished by the shoot ionome. We analyzed 18 elements in barley, cucumber and tomato and in two substrates (hydroponic vs soil) with different nutritional regimes. Multivariate analysis evidenced a clear separation between the species. In hydroponic conditions the main drivers separating the species are non essential-nutrients as Ti, Al, Na and Li, which were positively correlated with macro- (P, K) and micronutrients (Fe, Zn, Mo, B). The separation between species is confirmed when plants are grown on soil, but the distribution is determined especially by macronutrients (S, P, K, Ca, Mg) and micronutrients (B). A number of macro (Mg, Ca, S, P, K) and micronutrients (Fe, Mn, Zn, Cu, Mo, B) contribute to plant growth and several other important physiological and metabolic plant activities. The results reported here confirmed that the synergism and antagonism between them and other non-essential elements (Ti, Al, Si, Na) define the plant taxonomic character. The ionome profile might thus be exploited as a tool for the diagnosis of plants physiological/nutritional status but also in defining biofortification strategies to optimize both mineral enrichment of staple food crops and the nutrient input as fertilizers.

Genetics- and genomics-based interventions for nutritional enhancement of grain legume crops: status and outlook

Meeting the food demands and ensuring nutritional security of the ever increasing global population in the face of degrading natural resource base and impending climate change is the biggest challenge of the twenty first century. The consequences of mineral/micronutrient deficiencies or the hidden hunger in the developing world are indeed alarming and need urgent attention. In addressing the problems associated with mineral/micronutrient deficiency, grain legumes as an integral component of the farming systems in the developing world have to play a crucial role. For resource-poor populations, a strategy based on selecting and/or developing grain legume cultivars with grains denser in micronutrients, by biofortification, seems the most appropriate and attractive approach to address the problem. This is evident from the on-going global research efforts on biofortification to provide nutrient-dense grains for use by the poorest of the poor in the developing countries. Towards this end, rapidly growing genomics technologies hold promise to hasten the progress of breeding nutritious legume crops. In conjunction with the myriad of expansions in genomics, advances in other 'omics' technologies particularly plant ionomics or ionome profiling open up novel opportunities to comprehensively examine the elemental composition and mineral networks of an organism in a rapid and cost-effective manner. These emerging technologies would effectively guide the scientific community to enrich the edible parts of grain legumes with bio-available minerals and enhancers/promoters. We believe that the application of these new-generation tools in turn would provide crop-based solutions to hidden hunger worldwide for achieving global nutritional security.

Iron nutrition, biomass production, and plant product quality

One of the grand challenges in modern agriculture is increasing biomass production, while improving plant product quality, in a sustainable way. Of the minerals, iron (Fe) plays a major role in this process because it is essential both for plant productivity and for the quality of their products. Fe homeostasis is an important determinant of photosynthetic efficiency in algae and higher plants, and we review here the impact of Fe limitation or excess on the structure and function of the photosynthetic apparatus. We also discuss the agronomic, plant breeding, and transgenic approaches that are used to remediate Fe deficiency of plants on calcareous soils, and suggest ways to increase the Fe content and bioavailability of the edible parts of crops to improve human diet.

RIKEN tandem mass spectral database (ReSpect) for phytochemicals: a plant-specific MS/MS-based data resource and database

The fragment pattern analysis of tandem mass spectrometry (MS/MS) has long been used for the structural characterization of metabolites. The construction of a plant-specific MS/MS data resource and database will enable complex phytochemical structures to be narrowed down to candidate structures. Therefore, a web-based database of MS/MS data pertaining to phytochemicals was developed and named ReSpect (RIKEN tandem mass spectral database). Of the 3595 metabolites in ReSpect, 76% were derived from 163 literature reports, whereas the rest was obtained from authentic standards. As a main web application of ReSpect, a fragment search was established based on only the m/z values of query data and records. The confidence levels of the annotations were managed using the MS/MS fragmentation association rule, which is an algorithm for discovering common fragmentations in MS/MS data. Using this data resource and database, a case study was conducted for the annotation of untargeted MS/MS data that were selected after quantitative trait locus analysis of the accessions (Gifu and Miyakojima) of a model legume Lotus japonicus. In the case study, unknown metabolites were successfully narrowed down to putative structures in the website.

Elemental profiles reflect plant adaptations to the environment

Most mineral elements found in plant tissues come exclusively from the soil, necessitating that plants adapt to highly variable soil compositions to survive and thrive. Profiling element concentrations in genetically diverse plant populations is providing insights into the plant-environment interactions that control elemental accumulation, as well as identifying the underlying genes. The resulting molecular understanding of plant adaptation to the environment both demonstrates how soils can shape genetic diversity and provides solutions to important agricultural challenges.

Quantitative trait locus analysis of symbiotic nitrogen fixation activity in the model legume Lotus japonicus

Many legumes form nitrogen-fixing root nodules. An elevation of nitrogen fixation in such legumes would have significant implications for plant growth and biomass production in agriculture. To identify the genetic basis for the regulation of nitrogen fixation, quantitative trait locus (QTL) analysis was conducted with recombinant inbred lines derived from the cross Miyakojima MG-20 × Gifu B-129 in the model legume Lotus japonicus. This population was inoculated with Mesorhizobium loti MAFF303099 and grown for 14 days in pods containing vermiculite. Phenotypic data were collected for acetylene reduction activity (ARA) per plant (ARA/P), ARA per nodule weight (ARA/NW), ARA per nodule number (ARA/NN), NN per plant, NW per plant, stem length (SL), SL without inoculation (SLbac-), shoot dry weight without inoculation (SWbac-), root length without inoculation (RLbac-), and root dry weight (RWbac-), and finally 34 QTLs were identified. ARA/P, ARA/NN, NW, and SL showed strong correlations and QTL co-localization, suggesting that several plant characteristics important for symbiotic nitrogen fixation are controlled by the same locus. QTLs for ARA/P, ARA/NN, NW, and SL, co-localized around marker TM0832 on chromosome 4, were also co-localized with previously reported QTLs for seed mass. This is the first report of QTL analysis for symbiotic nitrogen fixation activity traits.

Biodiversity of mineral nutrient and trace element accumulation in Arabidopsis thaliana

In order to grow on soils that vary widely in chemical composition, plants have evolved mechanisms for regulating the elemental composition of their tissues to balance the mineral nutrient and trace element bioavailability in the soil with the requirements of the plant for growth and development. The biodiversity that exists within a species can be utilized to investigate how regulatory mechanisms of individual elements interact and to identify genes important for these processes. We analyzed the elemental composition (ionome) of a set of 96 wild accessions of the genetic model plant Arabidopsis thaliana grown in hydroponic culture and soil using inductively coupled plasma mass spectrometry (ICP-MS). The concentrations of 17-19 elements were analyzed in roots and leaves from plants grown hydroponically, and leaves and seeds from plants grown in artificial soil. Significant genetic effects were detected for almost every element analyzed. We observed very few correlations between the elemental composition of the leaves and either the roots or seeds. There were many pairs of elements that were significantly correlated with each other within a tissue, but almost none of these pairs were consistently correlated across tissues and growth conditions, a phenomenon observed in several previous studies. These results suggest that the ionome of a plant tissue is variable, yet tightly controlled by genes and gene × environment interactions. The dataset provides a valuable resource for mapping studies to identify genes regulating elemental accumulation. All of the ionomic data is available at www.ionomicshub.org.

Moving micronutrients from the soil to the seeds: genes and physiological processes from a biofortification perspective

The micronutrients iron (Fe), zinc (Zn), and copper (Cu) are essential for plants and the humans and animals that consume plants. Increasing the micronutrient density of staple crops, or biofortification, will greatly improve human nutrition on a global scale. This review discusses the processes and genes needed to translocate micronutrients through the plant to the developing seeds, and potential strategies for developing biofortified crops.

Variation and inheritance of iron reductase activity in the roots of common bean (Phaseolus vulgaris L.) and association with seed iron accumulation QTL

BACKGROUND

Iron deficiency anemia is a global problem which often affects women and children of developing countries. Strategy I plants, such as common bean (Phaseolus vulgaris L.) take up iron through a process that involves an iron reduction mechanism in their roots; this reduction is required to convert ferric iron to ferrous iron. Root absorbed iron is critical for the iron nutrition of the plant, and for the delivery of iron to the shoot and ultimately the seeds. The objectives of this study were to determine the variability and inheritance for iron reductase activity in a range of genotypes and in a low × high seed iron cross (DOR364 x G19833), to identify quantitative trait loci (QTL) for this trait, and to assess possible associations with seed iron levels.

RESULTS

The experiments were carried out with hydroponically grown plants provided different amounts of iron varying between 0 and 20 μM Fe(III)-EDDHA. The parents, DOR364 and G19833, plus 13 other cultivated or wild beans, were found to differ in iron reductase activity. Based on these initial experiments, two growth conditions (iron limited and iron sufficient) were selected as treatments for evaluating the DOR364 × G19833 recombinant inbred lines. A single major QTL was found for iron reductase activity under iron-limited conditions (1 μM Fe) on linkage group b02 and another major QTL was found under iron sufficient conditions (15 μM Fe) on linkage group b11. Associations between the b11 QTL were found with several QTL for seed iron.

CONCLUSIONS

Genes conditioning iron reductase activity in iron sufficient bean plants appear to be associated with genes contributing to seed iron accumulation. Markers for bean iron reductase (FRO) homologues were found with in silico mapping based on common bean synteny with soybean and Medicago truncatula on b06 and b07; however, neither locus aligned with the QTL for iron reductase activity. In summary, the QTL for iron reductase activity under iron limited conditions may be useful in environments where beans are grown in alkaline soils, while the QTL for iron reductase under sufficiency conditions may be useful for selecting for enhanced seed nutritional quality.

QTL for seed iron and zinc concentration and content in a Mesoamerican common bean (Phaseolus vulgaris L.) population

Iron and zinc deficiencies are human health problems found throughout the world and biofortification is a plant breeding-based strategy to improve the staple crops that could address these dietary constraints. Common bean is an important legume crop with two major genepools that has been the focus of genetic improvement for seed micronutrient levels. The objective of this study was to evaluate the inheritance of seed iron and zinc concentrations and contents in an intra-genepool Mesoamerican × Mesoamerican recombinant inbred line population grown over three sites in Colombia and to identify quantitative trait loci (QTL) for each mineral. The population had 110 lines and was derived from a high-seed iron and zinc climbing bean genotype (G14519) crossed with a low-mineral Carioca-type, prostrate bush bean genotype (G4825). The genetic map for QTL analysis was created from SSR and RAPD markers covering all 11 chromosomes of the common bean genome. A set of across-site, overlapping iron and zinc QTL was discovered on linkage group b06 suggesting a possibly pleiotropic locus and common physiology for mineral uptake or loading. Other QTL for mineral concentration or content were found on linkage groups b02, b03, b04, b07, b08 and b11 and together with the b06 cluster were mostly novel compared to loci found in previous studies of the Andean genepool or inter-genepool crosses. The discovery of an important new locus for seed iron and zinc concentrations may facilitate crop improvement and biofortification using the high-mineral genotype especially within the Mesoamerican genepool.