Rare genetic variation at Zea mays crtRB1 increases β-carotene in maize grain

Breeding to increase β-carotene levels in cereal grains, termed provitamin A biofortification, is an economical approach to address dietary vitamin A deficiency in the developing world. Experimental evidence from association and linkage populations in maize (Zea maysL.) demonstrate that the gene encoding β-carotene hydroxylase 1 (crtRB1) underlies a principal quantitative trait locus associated with β-carotene concentration and conversion in maize kernels. crtRB1 alleles associated with reduced transcript expression correlate with higher β-carotene concentrations. Genetic variation at crtRB1 also affects hydroxylation efficiency among encoded allozymes, as observed by resultant carotenoid profiles in recombinant expression assays. The most favorable crtRB1 alleles, rare in frequency and unique to temperate germplasm, are being introgressed via inexpensive PCR marker-assisted selection into tropical maize germplasm adapted to developing countries, where it is most needed for human health

Distinct Genetic Architectures for Male and Female Inflorescence Traits of Maize

We compared the genetic architecture of thirteen maize morphological traits in a large population of recombinant inbred lines. Four traits from the male inflorescence (tassel) and three traits from the female inflorescence (ear) were measured and studied using linkage and genome-wide association analyses and compared to three flowering and three leaf traits previously studied in the same population. Inflorescence loci have larger effects than flowering and leaf loci, and ear effects are larger than tassel effects. Ear trait models also have lower predictive ability than tassel, flowering, or leaf trait models. Pleiotropic loci were identified that control elongation of ear and tassel, consistent with their common developmental origin. For these pleiotropic loci, the ear effects are larger than tassel effects even though the same causal polymorphisms are likely involved. This implies that the observed differences in genetic architecture are not due to distinct features of the underlying polymorphisms. Our results support the hypothesis that genetic architecture is a function of trait stability over evolutionary time, since the traits that changed most during the relatively recent domestication of maize have the largest effects

Nitrogen mineralization from broiler litter applied to southeastern Coastal Plain soils

A field study was conducted to determine nitrogen (N) mineralization from broiler litter (EL) in two Coastal Plain soils of differing texture, sandy (Tifton loamy sand) or clayey (Greenville sandy clay loam). These soils represented the broad range in surface textures commonly found in soils used for agricultural production in the southeastern Coastal Plain. Published protocols used for the study were designed by the ARS mineralization team. In addition to measuring ammonium (NH4-N) and nitrate (NO3-N) in the soil as a measure of N mineralization, both total C and total N were measured to determine the impact of a single BL amendment on C sequestration and N accumulation. Amounts of N in the soil from BL mineralization over 70 days were identical for both soils, 46.4 mg N kg-1 soil (0.046%), but differences occurred in timing of the mineralization processes. In the sandy Tifton soil, depletion of NH4-N and nitrification of the NH4-N to NO3-N occurred simultaneously. The NH4-N from the BL was depleted in 21 days while peak NO3-N concentrations in the soil were found at 28 days. In the clayey Greenville soil, NH,-N concentrations from BL mineralization increased for 21 days and then decreased until reaching background levels by 70 days. Nitrate concentrations never did increase in the BL amended Greenville soil, indicating both that the nitrification rate was much slower than the ammonification race, and most likely, that what NO-N was produced was lost from the soil by denitrification under wet conditions. The combination of soil textural and microclimate differences along with greater protection of the BL residues in the clayey soil than in the sandy soil are believed responsible for the observed N mineralization differences between the two soils. Previous research has shown that N mineralization rate is positively correlated with sand content and negatively correlated with clay content of soils, and the results of this study concurred with those findings. Measurements of total C and total N in both Coastal Plain soils showed that overall increases were small with a single BL amendment, and it was concluded that long-term studies are needed to investigate C sequestration and N accumulation. It was concluded from the study that there is a high probability that BL mineralization rates will be significantly slower on the more clayey Coastal Plain soils than on very sandy ones, and that farm managers should take these rates into consideration when planning timing and amounts of BL applications

Rare genetic variation at Zea mays crtRB1 increases β-carotene in maize grain

Breeding to increase β-carotene levels in cereal grains, termed provitamin A biofortification, is an economical approach to address dietary vitamin A deficiency in the developing world. Experimental evidence from association and linkage populations in maize (Zea maysL.) demonstrate that the gene encoding β-carotene hydroxylase 1 (crtRB1) underlies a principal quantitative trait locus associated with β-carotene concentration and conversion in maize kernels. crtRB1 alleles associated with reduced transcript expression correlate with higher β-carotene concentrations. Genetic variation at crtRB1 also affects hydroxylation efficiency among encoded allozymes, as observed by resultant carotenoid profiles in recombinant expression assays. The most favorable crtRB1 alleles, rare in frequency and unique to temperate germplasm, are being introgressed via inexpensive PCR marker-assisted selection into tropical maize germplasm adapted to developing countries, where it is most needed for human health.This article is published as Yan, Jianbing, Catherine Bermudez Kandianis, Carlos E. Harjes, Ling Bai, Eun-Ha Kim, Xiaohong Yang, Debra J. Skinner et al. "Rare genetic variation at Zea mays crtRB1 increases β-carotene in maize grain." Nature genetics 42, no. 4 (2010): 322. doi: 10.1038/ng.551.</p