Grain composition and amino acid content in maize cultivars representing 80 years of commercial maize varieties

In order to determine how modern hybrids have impacted grain composition and amino acid content of the corn crop, we characterized a set of cultivars that were widely grown in different eras from the 1920s through 2001. Grain composition exhibited clear trends with time, with protein decreasing and starch increasing. The effects of different plant densities were examined. The grain protein content of modern hybrids responds to plant density and environment differently than the protein content of older varieties. These differences are consistent with a model in which protein content is modulated by different growth conditions. These differences may explain, in part, the mechanism by which modern hybrids maintain yield in different environments, i.e. reduction of protein content in stressful environments frees resources that are used to maintain yield. We examined the content of the nutritionally limiting essential amino acids lysine, methionine and tryptophan in grain of these cultivars. On a per tissue mass basis, the levels of these amino acids dropped with time while on a per protein basis, their levels were not significantly changed. We conclude that the development of modern hybrids has resulted in maize with reduced protein content, but the nutritional quality of this protein has not changed

Anthocyanins and antioxidant activity in coloured waxy corn at different maturation stages

The anthocyanin content and antioxidant activity of kernels from 12 genotypes of waxy corn at two maturation stages (milk and mature) were investigated. The individual anthocyanins contained in coloured waxy corn were identified and quantified by HPLC-DAD-ESI/MS analysis. Cyanidin-3-glucoside and its derivatives were detected as being most dominant. Furthermore, acylated anthocyanins constituted 67.1–88.2% and 46.2–83.6% of the total contents at the milk and mature stages, respectively. The concentration of monomeric anthocyanin increased throughout the development of each genotype of corn. The antioxidant activity, which was determined by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging ability, increased with ripening. However, the ferric reducing antioxidant power (FRAP) and Trolox equivalent antioxidant capacity (TEAC) revealed decreases in some genotypes during ripening. The kernels of a purplish black waxy corn genotype (KKU-WX111031) exhibited the greatest antioxidant activity and contained the highest level of anthocyanins among the genotypes tested at both maturation stages

Anthocyanin, phenolics and antioxidant activity changes in purple waxy corn as affected by traditional cooking

Antioxidant components, including anthocyanins and phenolic compounds, antioxidant activity, and their changes during traditional cooking of fresh purple waxy corn were investigated. As compared to the raw corn, thermal treatment caused significant (p ⩽ 0.05) decreases in each antioxidant compound and antioxidant activity. Steam cooking preserved more antioxidant compounds than boiling. Boiling caused a significant loss of anthocyanin and phenolic compounds into the cooking water. This cooking water is a valuable co-product because it is a good source of purple pigment. By comparing levels of antioxidant compounds in raw and cooked corn, we determined that degradation results in greater loss than leaching or diffusion into cooking water. Additionally, separation of kernels from the cob prior to cooking caused increased loss of antioxidant compounds

Accuracy and Training Population Design for Genomic Selection on Quantitative Traits in Elite North American Oats

Genomic selection (GS) is a method to estimate the breeding values of individuals by using markers throughout the genome. We evaluated the accuracies of GS using data from five traits on 446 oat (Avena sativa L.) lines genotyped with 1005 Diversity Array Technology (DArT) markers and two GS methods (ridge regression–best linear unbiased prediction [RR-BLUP] and BayesCπ) under various training designs. Our objectives were to (i) determine accuracy under increasing marker density and training population size, (ii) assess accuracies when data is divided over time, and (iii) examine accuracy in the presence of population structure. Accuracy increased as the number of markers and training size become larger. Including older lines in the training population increased or maintained accuracy, indicating that older generations retained information useful for predicting validation populations. The presence of population structure affected accuracy: when training and validation subpopulations were closely related accuracy was greater than when they were distantly related, implying that linkage disequilibrium (LD) relationships changed across subpopulations. Across many scenarios involving large training populations, the accuracy of BayesCπ and RR-BLUP did not differ. This empirical study provided evidence regarding the application of GS to hasten the delivery of cultivars through the use of inexpensive and abundant molecular markers available to the public sector

Selection of methionine-enriched soybean seeds

Protein accounts for approximately 40 % of the dry weight of a soybean seed; how­ ever, soy protein is deficient in both cysteine and methionine. To overcome this sulfur deficiency, animal feeders supplement soy protein rations with costly methio­ nine, which is more stable than cysteine. To alleviate the need for methionine supplementation, we mutagenized seeds and selected genetic soybean lines, the protein of which is enriched approximately 20 % for both cysteine and methionine. Animal rations prepared from these genetic lines should not require methionine supplemen­tation

Construction and evaluation of a maize (Zea mays) chimaeric promoter with activity in kernel endosperm and embryo

Chimaeric promoters contain DNA sequences from different promoters. Chimaeric promoters are developed to increase the level of recombinant protein expression, to precisely control transgene activity or to combat homology-based gene silencing. Sets of chimaeric promoters, each containing different lengths of DNA from maize (Zea mays) 27zn (27 kDa γ-zein) endosperm-specific promoter and the Glb1 (Globulin-1) embryo-specific promoter were created and tested in a transient expression assay of GFP (green fluorescent protein). Promoter fragments with the highest activity were combined to create the chimaeric promoter A27znGlb1. In the context of the chimaeric promoter, the selected Glb1 promoter fragment was necessary and sufficient to activate expression in embryo tissue and was functionally equivalent to the native Glb1 promoter. Similarly, the selected 27zn promoter fragment in the chimaeric promoter was necessary and sufficient to activate expression in endosperm tissue and was functionally equivalent to the native 27zn promoter. Maize transgenic plants containing the A27znGlb1 chimaeric promoter fused to GFP were produced to characterize this promoter in vivo. Quantitative reverse-transcriptase PCR was used to determine that the promoter was active in the embryo, endosperm, pericarp and immature leaf tissues. GFP activity in plants containing the chimaeric promoter was not significantly different in endosperm than the activity of GFP fused to the full-length 27zn promoter, nor was it different in embryo from the activity of GFP fused to the full-length Glb1 promoter. Transgene copy numbers were shown to be between 4 and 12 copies in different events

Maize Transgenes Containing Zein Promoters are Regulated by opaque2

Understanding epistatic interactions between transgenes and native genes is critical for predicting the response of transgenes to different genetic backgrounds and environments. Our objective was to determine if predicted epistatic interactions occur between maize (Zea mays L.) transgenes carrying zein promoters and opaque2, a transcriptional regulator of zein genes. Expression of the transgenes was significantly decreased in kernels containing the opaque2 mutation. Native zein proteins in these kernels were reduced as well. Thus, transgene expression mirrored expression of the native gene that contributed the promoter of the transgene. This work demonstrates that information about native gene expression may be useful for predicting transgene expression, reducing the risk of unintended consequences of transgene expression

Recurrent Selection for Transgene Activity Levels in Maize Results in Proxy Selection for a Native Gene with the Same Promoter

High activity levels of a transgene can be very useful, making a transgene easier to evaluate for safety and efficacy. High activity levels can also increase the economic benefit of the production of high value proteins in transgenic plants. The goal of this research is to determine if recurrent selection for activity of a transgene will result in higher activity, and if selection for activity of a transgene controlled by a native promoter will also increase protein levels of the native gene with the same promoter. To accomplish this goal we used transgenic maize containing a construct encoding green fluorescent protein controlled by the promoter for the maize endosperm-specific 27kDa gamma zein seed storage protein. We carried out recurrent selection for fluorescence intensity in two breeding populations. After three generations of selection, both selected populations were significantly more fluorescent and had significantly higher levels of 27kDa gamma zein than the unselected control populations. These higher levels of the 27kDa gamma zein occurred independently of the presence of the transgene. The results show that recurrent selection can be used to increase activity of a transgene and that selection for a transgene controlled by a native promoter can increase protein levels of the native gene with the same promoter via proxy selection. Moreover, the increase in native gene protein level is maintained in the absence of the transgene, demonstrating that proxy selection can be used to produce non-transgenic plants with desired changes in gene expression

Evaluation of Maize Germplasm from Saint Croix for Resistance to Leaf Feeding by Fall Armyworm

Maize (Zea mays L.) is a preferred host of fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera:Noctuidae), with larvae primarily feeding on developing leaves and ear tissue. The fall armyworm is resistant to several classes of insecticide and Bt-maize grown in certain areas. Native sources of plant resistance to the pest are available for public use, but new sources of resistance need to be discovered and developed. The objective for this study was to test maize germplasm collected from Saint Croix, U.S. Virgin Islands, for resistance to leaf feeding by fall armyworm. Plants were grown in the field and artificially infested at a high level. Scores of damage by fall armyworm feeding on leaves at 7 and 14 days differed significantly for the 13 maize genotypes tested. Scores at 14 days for Saint Croix Group 1 (5.8), Saint Croix Group 3 (5.6), Saint Croix 2 (5.6), and Saint Croix 7 (6.0) were moderately resistant and not significantly different from one another. Individual plants in the populations were variable for resistance to leaf feeding, and scored between 4 and 7. It should be possible to select within the populations for greater resistance to damage by fall armyworms feeding on leaves