Michael A. Grusak

Can We Improve the Nutritional Quality of Legume Seeds

The Food and Agriculture Organization statistics for 2001 ( ) show that 274 million metric tons of grain legumes were produced across the world, of which 177 million were soybeans ( Glycine max ; one-half of which were produced in the U.S.)

Inheritance of seed iron and zinc concentrations in common bean (Phaseolus vulgaris L.)

Micronutrients are essential elements needed in small amounts for adequate human nutrition and include the elements iron and zinc. Both of these minerals are essential to human well-being and an adequate supply of iron and zinc help to prevent iron deficiency anemia and zinc deficiency, two prevalent health concerns of the developing world. The objective of this study was to determine the inheritance of seed iron and zinc accumulation in a recombinant inbred line (RIL) population of common beans from a cross of lowxa0×xa0high mineral genotypes (DOR364xa0×xa0G19833) using a quantitative trait locus (QTL) mapping approach. The population was grown over two trial sites and two analytical methods (Inductively Coupled Plasma Spectrometry and Atomic Absorption Spectroscopy) were used to determine iron and zinc concentration in the seed harvested from these trials. The variability in seed mineral concentration among the lines was larger for iron (40.0–84.6xa0ppm) than for zinc (17.7–42.4xa0ppm) with significant correlations between trials, between methods and between minerals (up to rxa0=xa00.715). A total of 26 QTL were identified for the mineralxa0×xa0trialxa0×xa0method combinations of which half were for iron concentration and half for zinc concentration. Many of the QTL (11) for both iron (5) and zinc (6) clustered on the upper half of linkage group B11, explaining up to 47.9% of phenotypic variance, suggesting an important locus useful for marker assisted selection. Other QTL were identified on linkage groups B3, B6, B7, and B9 for zinc and B4, B6, B7, and B8 for iron. The relevance of these results for breeding common beans is discussed especially in light of crop improvement for micronutrient concentration as part of a biofortification program.

Genetic diversity, population structure and genome-wide marker-trait association analysis emphasizing seed nutrients of the USDA pea (Pisum sativum L.) core collection

Genetic diversity, population structure and genome-wide marker-trait association analysis was conducted for the USDA pea (Pisum sativum L.) core collection. The core collection contained 285 accessions with diverse phenotypes and geographic origins. The 137 DNA markers included 102 polymorphic fragments amplified by 15 microsatellite primer pairs, 36 RAPD loci and one SCAR (sequence characterized amplified region) marker. The 49 phenotypic traits fall into the categories of seed macro- and micro-nutrients, disease resistance, agronomic traits and seed characteristics. Genetic diversity, population structure and marker-trait association were analyzed with the software packages PowerMarker, STUCTURE and TASSEL, respectively. A great amount of variation was revealed by the DNA markers at the molecular level. Identified were three sub-populations that constituted 56.1%, 13.0% and 30.9%, respectively, of the USDA Pisum core collection. The first sub-population is comprised of all cultivated pea varieties and landraces; the second of wild P. sativum ssp. elatius and abyssinicum and the accessions from the Asian highland (Afghanistan, India, Pakistan, China and Nepal); while the third is an admixture containing alleles from the first and second sub-populations. This structure was achieved using a stringent cutoff point of 15% admixture (q-value 85%) of the collection. Significant marker-trait associations were identified among certain markers with eight mineral nutrient concentrations in seed and other important phenotypic traits. Fifteen pairs of associations were at the significant levels of P ≤ 0.01 when tested using the three statistical models. These markers will be useful in marker-assisted selection to breed pea cultivars with desirable agronomic traits and end-user qualities.

Quantitative trait locus analysis of root ferric reductase activity and leaf chlorosis in the model legume, Lotus japonicus

Background and aimsFerric reductase activity is a rate-limiting step in the accumulation of iron by Strategy I plants. Preliminary work with Lotus japonicus accessions Miyakojima MG-20 and Gifu B-129 identified differences in shoot chlorosis and ferric reductase activity. This study assessed the genetic basis for these differences.MethodsLines of a recombinant inbred population, derived from Miyakojima and Gifu, were tested for whole-root ferric reductase activity and shoot chlorosis following iron-limited growth. A ferric reductase gene (LjFRO1) was cloned from both parents. Protein sequence analysis, transcript abundance, and yeast complementation studies were conducted with the two parental alleles.ResultsA single quantitative trait locus (QTL) was identified for both ferric reductase activity and shoot chlorosis, with each QTL explaining ~30% of the variation and both overlapping across the same region of chromosome 3. LjFRO1 mapped to chromosome 3, but to a region adjacent to the reductase and chlorosis loci. Nucleotide variation in LjFRO1 parental alleles was identified, as were minor functional differences between the two proteins.ConclusionsThe results indicate that both allelic variation (providing potential functional differences) and unidentified molecular components (derived from non-LjFRO1 genetic loci) can contribute to the regulation of ferric reductase activity and chlorosis susceptibility.

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

BackgroundMarker-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.ResultsIn 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 1310.1xa0cM. 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.ConclusionThe 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.

Status and Future Developments Involving Plant Iron in Animal and Human Nutrition

Iron is an essential nutrient for humans and other animals, and must be consumed in adequate amounts to ensure proper growth and development, as well as good health of the organism. Dietary sources of iron can be divided into two types: non-heme iron, mostly provided by plant foods, and heme iron, present in animal foods. Heme iron intake is usually low for the majority of humans in many developing countries because of the high cost of animal products or due to cultural constraints concerning these foods. Heme iron intake also is low in most livestock, whose major source of dietary iron comes from forages and cereal crops. For these reasons, both humans and animals rely on plants as an important source of dietary iron. However, the iron concentration of plant foods varies greatly, and low concentrations in some common food sources make it difficult for humans and animals to meet daily dietary requirements when these foods are consumed in suggested amounts. Additionally, certain food components, such as phytate or tannins, can lower the bioavailablity of the iron that is in plant foods, thereby lowering its effective concentration even more. In order to improve the iron nutritional value of crop plants and consequently to improve human and animal health, several strategies are being utilized by plant scientists. These include: cultivar evaluation, plant breeding and marker-assisted selection, alteration of pathways of iron metabolism, and modification of iron bioavailability. In this review, we present the role that plant iron plays in the diets of humans and other animals, and discuss the strategies that can be employed to improve our plant-based food supply.

Plant Macro- and Micronutrient Minerals

All plants must obtain a number of inorganic mineral elements from their environment to ensure successful growth and development of both vegetative and reproductive tissues. These minerals serve numerous functions: as structural components in macromolecules, as cofactors in enzymatic reactions, as osmotic solutes needed tomaintain proper water potential, or as ionized species to provide charge balance in cellular compartments. Minerals can be divided into two classes, based on the relative amounts needed for plant growth (see Table 1). The macronutrients include nitrogen (N), potassium (K), calcium (Ca), magnesium (Mg), phosphorus (P) and sulfur (S); these are generally found in plants at concentrations greater than 0.1% of dry tissue weight. The currently recognized micronutrients include iron (Fe), zinc (Zn), manganese (Mn), copper (Cu), boron (B), chlorine (Cl), molybdenum (Mo) and nickel (Ni); these generally are found at concentrations less than 0.01% of dry tissue weight. These 14 minerals, along with the elements carbon (C), hydrogen (H) and oxygen (O), are broadly accepted as essential for the growth of all plants. Additional minerals, such as cobalt (Co), sodium (Na), silicon (Si), selenium (Se), iodine (I) and vanadium (V), have been shown to be essential or beneficial for certain plant species, but their widespread essentiality has yet to be established. Many other elements can be found in plants (over half the elements in the periodic table have been identified in some plant tissue), but these are thought to enter plants nonselectively. Most of these nonessential elements confer no known benefit to the plant, and many, such as cadmium (Cd) or chromium (Cr), are actually detrimental to plant growth.

Nutritional composition and cooking characteristics of tepary bean (Phaseolus acutifolius Gray) in comparison with common bean (Phaseolus vulgaris L.)

Tepary bean is a highly abiotic stress tolerant orphan crop for which there has been limited research on its nutritional value and cooking characteristics. These are key aspects when considering the potential for broader adoption of tepary bean. Therefore, the goal of this study was to evaluate a large set of seed composition and cooking traits related to human nutrition using both landraces and breeding lines of domesticated tepary bean from replicated field trials and to compare the traits in tepary with those in common bean. Tepary bean showed reduced fat and ash concentration and higher sucrose concentration as compared to common bean. Of the twelve amino acids evaluated, only proline in one of the two trials was statistically different between the two species. There were statistically significant differences between tepary and common bean for the concentration of some elements in this study; however, the elemental concentrations fell within the range of those found for common bean in previous studies. The majority of tepary bean lines showed consistently short cooking times and a high percentage of seeds showed measurable water uptake, while some showed a hardshell trait (low water uptake) and longer cooking times. Principal component analysis on a subset of traits showed a distinct group of common beans and two tepary bean groups that were divided on the basis of several agronomic, cooking, and elemental composition traits. Tepary bean, as with other pulses, is a highly nutritious crop with the range of composition and cooking characteristics similar to those of common bean. The variability for seed composition and cooking traits found within tepary bean can be exploited for its improvement.

Genome-wide association analysis of nutritional composition-related traits and iron bioavailability in cooked dry beans (Phaseolus vulgaris L.)

Seed nutrients in legumes are important for human health, particularly in developing countries with heavy reliance on plant-based diets, and among vegetarians in developed nations. Here, we report on our efforts to uncover the genetic basis underlying the phenotypic variation for protein, zinc, calcium concentrations, and iron bioavailability present in 206 accessions of dry bean (Phaseolus vulgaris L.) from the Andean Diversity Panel (ADP). We used 8111 single nucleotide polymorphisms (SNPs) generated with genotyping-by-sequencing (GBS) to examine the allelic variants’ associations with seed protein, zinc, and calcium concentrations, and iron bioavailability in the 206 ADP accessions grown over 2xa0years in Michigan. These efforts identified phenotypic variation among the ADP genotypes for each of the traits, with the highest variation (5.4-fold) found for cooked seed iron bioavailability. In addition, significant SNP-trait associations were found and explained from 6.3 to 13.2% of the phenotypic variation. These results expand the current understanding of the genetic architecture underlying these complex nutritional quality traits and iron bioavailability in dry beans. Furthermore, they have utility for future nutritional quality breeding efforts to better biofortify dry bean through genomics-assisted breeding.

Genetic diversity and association mapping of mineral element concentrations in spinach leaves

BackgroundSpinach is a useful source of dietary vitamins and mineral elements. Breeding new spinach cultivars with high nutritional value is one of the main goals in spinach breeding programs worldwide, and identification of single nucleotide polymorphism (SNP) markers for mineral element concentrations is necessary to support spinach molecular breeding. The purpose of this study was to conduct a genome-wide association study (GWAS) and to identify SNP markers associated with mineral elements in the USDA-GRIN spinach germplasm collection.ResultsA total of 14 mineral elements: boron (B), calcium (Ca), cobalt (Co), copper (Cu), iron (Fe), potassium (K), magnesium (Mg), manganese (Mn), molybdenum (Mo), sodium (Na), nickel (Ni), phosphorus (P), sulfur (S), and zinc (Zn) were evaluated in 292 spinach accessions originally collected from 29 countries. Significant genetic variations were found among the tested genotypes as evidenced by the 2 to 42 times difference in mineral concentrations. A total of 2402 SNPs identified from genotyping by sequencing (GBS) approach were used for genetic diversity and GWAS. Six statistical methods were used for association analysis. Forty-five SNP markers were identified to be strongly associated with the concentrations of 13 mineral elements. Only two weakly associated SNP markers were associated with K concentration. Co-localized SNPs for different elemental concentrations were discovered in this research. Three SNP markers, AYZV02017731_40, AYZV02094133_57, and AYZV02281036_185 were identified to be associated with concentrations of four mineral components, Co, Mn, S, and Zn. There is a high validating correlation coefficient with ru2009>u20090.7 among concentrations of the four elements. Thirty-one spinach accessions, which rank in the top three highest concentrations in each of the 14 mineral elements, were identified as potential parents for spinach breeding programs in the future.ConclusionsThe 45 SNP markers strongly associated with the concentrations of the 13 mineral elements: B, Ca, Co, Cu, Fe, Mg, Mn, Mo, Na, Ni, P, S, and Zn could be used in breeding programs to improve the nutritional quality of spinach through marker-assisted selection (MAS). The 31 spinach accessions with high concentrations of one to several mineral elements can be used as potential parents for spinach breeding programs.