Simultaneous Dissection of Grain Carotenoid Levels and Kernel Color in Biparental Maize Populations with Yellow-to-Orange Grain

ABSTRACT Maize enriched in provitamin A carotenoids could be key in combatting vitamin A deficiency in human populations relying on maize as a food staple. Consumer studies indicate that orange maize may be regarded as novel and preferred. This study identifies genes of relevance for grain carotenoid concentrations and kernel color, through simultaneous dissection of these traits in 10 families of the U.S. maize nested association mapping panel that have yellow to orange grain. Quantitative trait loci (QTL) were identified via joint-linkage analysis, with phenotypic variation explained for individual kernel color QTL ranging from 2.4 to 17.5%. These QTL were cross-analyzed with significant marker-trait associations in a genome-wide association study that utilized ∼27 million variants. Nine genes were identified: four encoding activities upstream of the core carotenoid pathway, one at the pathway branchpoint, three within the α- or β-pathway branches, and one encoding a carotenoid cleavage dioxygenase. Of these, three exhibited significant pleiotropy between kernel color and one or more carotenoid traits. Kernel color exhibited moderate positive correlations with β-branch and total carotenoids and negligible correlations with α-branch carotenoids. These findings can be leveraged to simultaneously achieve desirable kernel color phenotypes and increase concentrations of provitamin A and other priority carotenoids.

Introduction of a New Interesting Walnut Cultivar “Leto”

Ιn an effort to create walnut cultivars (Juglans regia) with high productivity, fruit quality and lateral bearing, a new cultivar, named “Leto”, was created by the cross “Gustine” × “Pedro”. Its main phenological and pomological characteristics were assessed according to the criteria of IPGR (1994) and UPOV-TG/125/6 (1999), for 10 consecutive years and compared with its maternal cultivars and “Chandler”. Observations showed that “Leto” has high lateral bearing habit (90%) and presents satisfactory yield at the full production age. The tree size is smaller than that of its parents and “Chandler”, female flowers bloom from 11 to 22 of April and male from 3 to 6 of April. “Leto” nuts are harvested at the end of September, present easy hull dehiscence and high kernel percentage. Other positive nut characteristics of “Leto” are light kernel color, well kernel filling and easy removal of the kernel halves. “Leto” is a mid-early cultivar of great interest due to its high- quality nuts, suitable for dense plantings, in regions where the last spring frosts occur in late March to early April, thus, making it a promising cultivar for Greece, but also for other regions with similar geomorphological and climatic conditions.

Trait Association and Prediction Through Integrative K-mer Analysis

Genome-wide association study (GWAS) with single nucleotide polymorphisms (SNPs) has been widely used to explore genetic controls of phenotypic traits. Here we employed an GWAS approach using k-mers, short substrings from sequencing reads. Using maize cob and kernel color traits, we demonstrated that k-mer GWAS can effectively identify associated k-mers. Co-expression analysis of kernel color k-mers and pathway genes directly found k-mers from causal genes. Analyzing complex traits of kernel oil and leaf angle resulted in k-mers from both known and candidate genes. Evolution analysis revealed most k-mers positively correlated with kernel oil were strongly selected against in maize populations, while most k-mers for upright leaf angle were positively selected. In addition, phenotypic prediction of kernel oil, leaf angle, and flowering time using k-mer data showed at least a similarly high prediction accuracy to the standard SNP-based method. Collectively, our results demonstrated the bridging role of k-mers for data integration and functional gene discovery.

Simultaneous Dissection of Grain Carotenoid Levels and Kernel Color in Biparental Maize Populations with Yellow-to-Orange Grain

ABSTRACTMaize enriched in provitamin A carotenoids could be key in combatting vitamin A deficiency in human populations relying on maize as a food staple. Consumer studies indicate that orange maize may be regarded as novel and preferred. This study identifies genes of relevance for grain carotenoid concentrations and kernel color, through simultaneous dissection of these traits in 10 families of the U.S. maize nested association mapping population that have yellow to orange grain. Quantitative trait loci (QTL) were identified via joint-linkage analysis, with phenotypic variation explained for individual kernel color QTL ranging from 2.4 to 17.5%. These QTL were cross-analyzed with significant marker-trait associations in a genome-wide association study that utilized ∼27 million variants. Nine genes were identified: four encoding activities upstream of the core carotenoid pathway, one at the pathway branchpoint, three within the α- or β-pathway branches, and one encoding a carotenoid cleavage dioxygenase. Of these, three exhibited significant pleiotropy between kernel color and one or more carotenoid traits. Kernel color exhibited moderate positive correlations with β-branch and total carotenoids and negligible correlations with α-branch carotenoids. These findings can be leveraged to simultaneously achieve desirable kernel color phenotypes and increase concentrations of provitamin A and other priority carotenoids.

Measuring antioxidant activity in yellow corn (Zea mays L.) inbreds from three different geographic regions

Corn (Zea mays L.) provides a major source of calories for human consumption and therefore, the nutritional components of corn have a large impact on human health. For example, corn kernels contain antioxidants, such as polyphenols (including anthocyanins and other flavonoids) and carotenoids. Such compounds represent useful targets for biofortification breeding. In this study, we used 34 corn inbred lines from three different regions (East Asia, Southern Asia, and subtropical regions) and 11 F1 hybrids derived from the inbreds to investigate antioxidant activity in yellow corn. We compared different methods for measuring antioxidant activity to test their consistency and to determine whether color could be used as an indicator of antioxidant activity. We also measured carotenoid levels in yellow corn. No difference in antioxidant activity was detected between inbred corn lines from temperate vs. tropical regions. We determined that carotenoid is a major contributor to antioxidant activity in yellow corn and that kernel color, especially yellowness, could be used as an indicator of antioxidant activity in yellow corn. These findings lay the foundation for the biofortification of yellow corn by providing information about the correlations among kernel color, carotenoid contents, and antioxidant activity and by identifying an easy method to assess antioxidant activity in yellow corn.

Physical, Nutritional and Functional Properties of Walnuts Genotypes (Juglans regia L.) from Romania

Walnut (Juglans regia L.) is the oldest fruit grown in the world and grows spontaneously almost throughout Romania. In this study, the physical properties and chemical composition of twenty types of walnuts from three different locations in Romania were studied. The physical analyzes that were performed were: walnut dimensions and shape properties (nut diameter, nut length, nut shape and nut size), fruit properties (walnut weight, walnut kernel weight and percentage of kernel) and external properties of walnut (walnut kernel extraction, kernel color and shell roughness). The proximate chemical composition (content of water, ash, lipids, proteins and carbohydrates) was determined by standardized AOAC methods, while fatty compounds were determined by GSMS. Water content ranged from 1.23% to 5.00%, mineral content between 1.31% and 2.49%, lipids content between 56.09% and 66.56% and protein content ranged between 12.73% and 20.413%. Based on these, the carbohydrate content and nutritional value of the 20 walnut samples were calculated. In all samples, saturated palmitic acid (C16:0) and stearic acid (C18:0) as well as unsaturated oleic (C18:1), linoleic (C18:2) and linolenic (C18:3) fatty acids were determined. A statistical analysis was also performed correlating the results obtained from the chemical analyzes of the walnuts.

Genotypic and Environmental Variations in Kernel Color Indices in the Main Almond (Prunus dulcis (Mill.) D.A. Webb) Cultivars Grown in North-Eastern Morocco

Color indices are important quality traits that define the consumer visual acceptance and agroindustrial preferences. Little is known regarding these properties in the commercial almond cultivars grown in Morocco. This work aimed at investigating kernel color indices in five cultivars, namely, “Fournat de Brézenaud,” “Tuono,” “Ferragnès,” “Ferraduel,” and “Marcona.” Color indices consisted in the following: brightness (L∗), redness index (a∗), yellowness index (b∗), chroma (C∗), hue (H∗), and metric saturation (S∗). Measurements were performed over three consecutive growing seasons (2016–2018) across five different sites from northern (Aknoul, Bni Hadifa, and Tahar Souk) and eastern (Rislane and Sidi Bouhria) Morocco. All factors (cultivar, growing season, and site) affected significantly studied color properties; however, genotype was the main variability source. Wide variabilities were found among cultivars. “Marcona” showed the highest L∗, while “Ferragnès” and “Ferraduel” displayed greater scores of a∗, b∗, C∗, and S∗. Sidi Bouhria presented the lowest L∗ but higher a∗, H∗, and S∗. Moreover, Bni Hadifa displayed higher L∗, b∗, and C∗. 2016 (drier growing season) had the highest values of most indices. Principal component analyses (PCA) discriminate all factors through the first three components: PC1 (61%, genetic component) and PC2 (30%) and PC3 (7%) which were of environmental nature since they separate sites and growing seasons, respectively. Despite environmental effects, we suggested a possible discrimination among the studied cultivars based on their kernel color indices. Drought conditions during fruit development seemed to improve kernel quality via synthesis of pigments resulting in higher a∗ and b∗.

Transposon-induced inversions activate gene expression in Maize pericarp

Chromosomal inversions can have considerable biological and agronomic impacts including disrupted gene function, change in gene expression and inhibited recombination. Here we describe the molecular structure and functional impact of six inversions caused by Alternative Transpositions between p1 and p2 genes responsible for floral pigmentation in maize. In maize line p1-wwB54, the p2 gene is expressed in anther and silk but not in pericarp, making the kernels white. We identified inversions in this region caused by transposition of Ac and fractured Ac (fAc) transposable elements. These inversions change the position of a p1 enhancer and activate the expression of p2 in the kernel pericarp, resulting in red kernel color. We hypothesize that these inversions place the p2 gene promoter near a p1 gene enhancer, thereby activating p2 expression in kernel pericarp.