2013. The genetic architecture of maize domestication and range expansion

2013. The genetic architecture of maize domestication and range expansion

DOWNLOAD: PDF
SÐT: 0981800855 (A. LONG)
PRICE: 100.000 VND
EMAIL: FOODCROPS@GMAIL.COM

Abstract

The genetic architecture of the evolution of extreme morphological divergence is one of the fundamental questions of evolutionary biology. Maize (Zea Mays ssp. mays) and its wild ancestor, teosinte (Zea mays ssp. parviglumis) provide an ideal model for examining this question in part because of their extreme phenotypic divergence in plant architecture, ear morphology, and environmental range. In order to examine the genetic changes underlying this divergence, we use a population of maize-teosinte BC2S3 RILs. Using these RILs allows us to examine genetic architecture on multiple levels. First, whole genome QTL mapping is used to explore the diversity of genetic architectures which control domestication traits. These genetic architectures range from nearly Mendelian to polygenic. For two near Mendelian traits, glume architecture and barren ear base, the largest QTL contained a single gene in the 1.5 LOD confidence interval. The most polygenic trait was ear diameter, for which we found 35 QTL of varying effect sizes. As part of this project we extended the capabilities of the statistical program R/qtl to apply to a wider variety of experimental crosses. In order to examine the causes of extreme morphological divergence on the single gene level, we fine-mapped a single gene, ZmCCT which controls an approximately 9 day difference in flowering time between the homozygous maize and teosinte classes. We demonstrate that the causative difference is cis-regulatory, as under long day lengths ZmCCT alleles from diverse teosintes were consistently expressed at a higher level than the corresponding temperate maize alleles. Taken together these results provide examples of the variety of ways in which complex traits evolve .

2013. Quantitative genetic analysis of 16 maize populations adapted to the northern US corn belt

2013. Quantitative genetic analysis of 16 maize populations adapted to the northern US corn belt

DOWNLOAD: PDF
SÐT: 0981800855 (A. LONG)
PRICE: 100.000 VND
EMAIL: FOODCROPS@GMAIL.COM

ABSTRACT

Genetic diversity is essential for genome sequencing and a key contributor to increase frequency of favorable alleles for maize improvement. The objectives of this study were to determine the genetic components, assess the genetic diversity, and propose the heterotic grouping of a large sample of short-season maize populations based on multiple traits. Sixteen maize populations were included in a diallel mating design that followed Gardner-Eberhart Analysis (GEAN) II to estimate variety (v,) and heterosis (hy) genetic effects. The general combining ability (g;) estimates were also determined and used to classify the populations based on their genetic diversity. Data were generated in partially balanced single lattice experiments  across North Dakota (ND) locations in 2010,2011, and 2012. Combined analyses of variance showed significant differences among genotypes. Heterosis effects explained the most among dial lei entries sum of squares for grain yield, while v,- effects had greater influence on grain quality traits. The g, effects agreed with the genetic effect that had larger contribution to the total among diallel entries sum of squares for various traits. Three groups were formed based on the genetic distances (GD) of the g, estimates. Four heterotic groups were established based on s,j estimates for grain yield. Close correspondence was observed between the groups formed using GD and stj. The heterotic grouping among populations agreed with their genetic background information and heterotic group’s specific and general combining ability (HSGCA) estimates. The EARLYGEM 21 populations having exotic background were assigned to a unique heterotic group. The heterotic groups established among these populations will increase breeding efficiency to improve and develop genetically broad-based populations. Inter-population recurrent selection programs can be employed for population crosses with high grain yield and above average grain quality formed by parental populations belonging to different heterotic groups. Intra-population recurrent selection programs can also be established for the parental populations identified with desirable grain quality traits. These populations will serve as unique germplasm sources of short-season diverse inbred lines to produce the next generation of diverse northern U.S. hybrids. New heterotic patterns have been established as a source of new commercially viable single-cross and population hybrids  .

2012. Genetic analysis of cell expansion during maize leaf development

2012. Genetic analysis of cell expansion during maize leaf development

DOWNLOAD: PDF
SÐT: 0981800855 (A. LONG)
PRICE: 100.000 VND
EMAIL: FOODCROPS@GMAIL.COM

ABTRACT

The growth and development of plants requires a finely tuned and exquisitely controlled sequence of events, including cell division and expansion. Efforts in the Sylvester lab have focused on understanding the mechanisms of cell expansion during maize leaf development. In this dissertation, the role of several proteins in cell expansion is investigated. First, evidence is presented that Z/77RAB2A1, a small guanosine-triphosphatase (GTPase) of the Ras superfamily, is localized to the Golgi in growing leaf cells. The localization pattern of this protein primarily to the Golgi and only secondarily to the ER, suggests a diversified, or altered, function from that observed in other eukaryotes and dicots. The research here shows that ZmRab2Al is differentially expressed in cells primarily undergoing cytokinesis and cell expansion, but is not highly expressed in fully differentiated, non-expanding tissue. Disruption of ZmRab2Al by transposon insertion correlates with an overexpansion phenotype in leaf epidermal cells. This report represents the first association of a RAB, or any portion of the vesicle transport machinery, with anisotropic cell expansion. The results presented here suggest a diversified function for the RAB2-family protein trafficking pathway in monocot cells when compared to either dicots or to animals.

A major goal of the research was to determine the subcellular localization of ZmRAB2Al, a critical step for determining its function. To accomplish this goal, an efficient method for transient transformation of maize leaf tissue was developed. This method is amenable to expressing genes that are encoded either by their cDNAs or in their intact genomic context (i.e., with regulatory sequences and introns present). The technique can also be used for expressing constructs that have been cloned into GATEWAY plasmids and so could be used for semi-high throughput expression studies, particularly due to the potential for simultaneous transient expression of multiple genes. This technique will simplify subcellular localization studies, and will also likely be useful for a wider variety of techniques, such as functional studies with rationally-designed, dominant-negative alleles or mislocalization studies with plant chromobodies. This technique is expected to be a major breakthrough for maize functional genetics.

Finally, the wartyl-0 allele was cloned using positional cloning techniques and shown shown here to encode ZmCSLD1, a member of the CELLULOSE SYNTHASE-LIKE superfamily predicted to be involved in the biosynthesis of cell wall material. Two other amino acid substitutions in this protein that result in mutant phenotypes, in the warty 1-bumpy and wartyl-rough liueate alleles, were also identified. In the absence of a crystal structure for any plant cellulose synthase protein, this work contributes to the understanding of amino acids that are essential for normal function in this protein. These alleles should also prove useful as material for further genetic screens, such as enhancer and suppressor screens that will identify additional key factors involved in cell wall biosynthesis and deposition.
 

The research presented here demonstrates that ZmRAB2Al and ZwCLSDl contribute to normal cell expansion in maize. These findings, along with the establishment of a novel method for transient gene expression in maize leaf tissue, provide insight into mechanisms of cell expansion and offer new tools that increase the experimental and engineering potential of maize as a major crop plant .

2010. Marker assisted selection and breeding for desirable thinner pericarp thickness and ear traits in fresh market waxy corn germplasm

2010. Marker assisted selection and breeding for desirable thinner pericarp thickness and ear traits in fresh market waxy corn germplasm

DOWNLOAD: PDF
SÐT: 0981800855 (A. LONG)
PRICE: 100.000 VND
EMAIL: FOODCROPS@GMAIL.COM

ABSTRACT

Kernel pericarp thickness and ear architectural traits arc important selection criteria in fresh waxy com breeding programs as they are associated with consumer sensory and visual preferences. An F2:3 mapping population from the cross between South Korean inbreds BH20 and BH30 was developed in order to estimate genetic relationships among pericarp thickness traits and car architectural traits, and to identify QTL regions for these traits through univariate and multivariate approaches. High correlations among pericarp thickness traits were detected and QTL regions associated with multiple pericarp thickness traits were identified. Through incorporating principal component analysis (PCA) of pericarp thickness traits and car traits with QTL analysis, we detected PC-QTL regions that appear to have pleiotropic effects on multiple traits, particularly the pericarp traits on different parts of the kernel. The pericarp thickness QTL information was used to perform marker assisted selection to pyramid favorable QTL, as well as validate pericarp QTL. The MAS population was designed to try and maintain favorable ear traits by making crosses between lines chosen for favorable ear and pericarp thickness phenotypes and lines chosen for favorable QTL alleles for pericarp thickness traits. A few ear traits showed weak but favorable associations with pericarp thickness traits. Evaluation of the MAS population revealed that most selected QTL markers were significant for at least one pericarp thickness trait. Comparing groups of lines in the MAS population sorted by: phenotypes for thinner pericarp; favorable QTL alleles for pericarp thickness; and unfavorable alleles for pericarp thickness from MAS population, we found that in some cases that marker based selection might be effective for reducing pericarp thickness. Pyramiding significant favorable marker alleles showed reduction of pericarp thickness on all kernel regions. Since tcstcross performance (TP) is ultimately more important than per se line performance (LP), a testcross population was generated for groups of selected lines from MAS population. This was done to enable assessment of the effect of groups of lines and different testers, and to compare LP with TP. Group 1 with most favorable alleles showed significantly thinner pericarp than group 2 with fewest favorable alleles in testcross evaluation, regardless of tester. The TP with tester BH1030, which was the thinner pericarp testcross hybrid showed thinner pericarp than TP with tester Bl 11020. We found evidences that suggested the tester had dominance effects on reducing pericarp thickness in testcross population. In summary, pericarp thickness QTL information was useful for marker assisted selection of favorable loci within Korean germplasm, and therefore offers the potential to be useful for introgression of these favorable loci into more adapted U.S. germplasm. Weak but favorable relationships among pericarp thickness and some ear traits could be used collectively to improve overall features through independent selection in a fresh waxy com breeding program  .

2010. Genome wide association mapping and detection of copy-number variations in maize

2010. Genome wide association mapping and detection of copy-number variations in maize

DOWNLOAD: PDF
SÐT: 0981800855 (A. LONG)
PRICE: 100.000 VND
EMAIL: FOODCROPS@GMAIL.COM

ABSTRACT

The identification of genes responsible for phenotypes represents a central genetic problem. Specific methods and experimental designs are needed in order to elucidate complex phenotypes. These methodologies usually depend on the development of a suitable population of individuals and appropriate techniques to investigate DNA polymorphisms in that population. Two independent projects are presented here to improve the investigation of gene-phenotype associations and also the investigation of DNA polymorphisms in plant genetics. In the first, genome-wide association mapping of SNPs with oleic acid content in maize kernel is presented, including a comprehensive introduction and analysis of this methodology in comparison to classical QTL mapping. This is one of the first reports in the field implementing novel methods, detecting a gene responsible for a QTL, validating the locus, and showing common pitfalls that can occur in such projects. In the second, structural variations were detected among 13 maize inbred lines demonstrating that this kind of DNA polymorphism is a common feature in the maize genome and probably associated with plant phenotypes. Together these two projects provide an important contribution to the field of plant genetics laying the ground for future investigations and also their application in plant breeding  .

2009. The genetic architecture of maize photoperiod sensitivity as defined by recombinant inbred line backcross, and heterogeneous inbred family populations.

2009. The genetic architecture of maize photoperiod sensitivity as defined by recombinant inbred line backcross, and heterogeneous inbred family populations.

DOWNLOAD: PDF
SÐT: 0981800855 (A. LONG)
PRICE: 100.000 VND
EMAIL: FOODCROPS@GMAIL.COM

ABSTRACT

Tropical maize germplasm has frequently been cited as a potential source of enhanced genetic diversity that could be used to increase corn productivity. One obstacle to utilizing tropical maize germplasm in temperate breeding programs is photoperiod sensitivity, which is very common in tropical adapted maize lines. An investigation of the quantitative trait loci (QTL) contributing to maize photoperiod sensitivity may increase the facility with which maize breeders can adapt tropical maize germplasm to temperate latitudes.

The photoperiod sensitive phase of maize was studied in a diverse set of inbreds. From a factorial mating of two temperate and two tropical inbreds, four populations of recombinant inbred lines (RIL) were developed for the purpose of mapping the QTL underlying photoperiod sensitivity in tropical maize. Plants were grown in both long- and short-day environments and a number of traits were measured in each environment. These traits include flowering time, plant height, leaf number, and ear structure traits. The trait differences between long- and short-day environments were reported as the photoperiodic responses of the RILs. Utilizing the data of both individual and combined mapping populations, QTL were identified using iterative QTL mapping (iQTLm). The positions and effects of these QTL were compared between populations and with flowering time, plant height, and leaf number QTL from other mapping studies. We detected four regions in the genome that produced large photoperiodic effects and named these Zea mays Photoperiodic Response 1-4 (ZmPRl, ZmPR2, ZmPR3, and ZmPR4). Similar QTL positions have been detected by other researchers studying photoperiod sensitivity and flowering time in maize. In addition to a major QTL on chromosome 3, QTL affecting the tasseled ear phenotype of maize were also found in the ZmPR3 and ZmPR4 QTL regions, implicating these QTL as also having effects on floral morphology. The four ZmPR loci are the most promising targets of marker-assisted selection against photoperiod sensitivity in maize.

Verification of the four ZmPR QTL was undertaken in four BC2F3:4 mapping populations, each having B73 as the recurrent parent. The CML254 backcross population had the same parentage as one of the RIL populations originally used to identify the ZmPR loci. We verified the presence of three of the four ZmPR loci in this population. We also found that the other three mapping populations, derived from CML247, Ki3, and Kil 1 showed significant flowering time and plant height associations at some of the ZmPR loci. Winter nurseries were used to verify that the ZmPR4 QTL, which was the strongest photoperiodic flowering time QTL detected in previous mapping studies, was indeed a photoperiodic and not flowering time per se QTL. An Ft population derived from a Kil 4 x CML254 cross was used to identify functional allelic differences among these two tropical lines at the ZmPR loci. Alleles of Ki 14 and CML254 were functionally distinct at ZmPR4 and ZmPR2.

The utility of QTL mapping for applied breeding programs is often limited by the transferability of QTL across populations and by the lack of precision in QTL mapping. One solution to these obstacles is to fine-map and clone the gene or genes underlying the QTL. I developed several heterogeneous inbred families (HIFs) from four RIL populations in order to facilitate fine-mapping. I observed several traits in these HIFs in phytotron, greenhouse, and field environments. I report the manner with which the HIFs were derived, as well as some observations and notes about future fine-mapping directions with these HIFs  .

2009. Regulation of aleurone cell fate determinants in Zea mays

2009. Regulation of aleurone cell fate determinants in Zea mays

DOWNLOAD: PDF
SÐT: 0981800855 (A. LONG)
PRICE: 100.000 VND
EMAIL: FOODCROPS@GMAIL.COM

INTRODUCTION

 
Human nutrition is provided by a limited number of plant species. About 90% of mankind’s food supply is derived from approximately 17 species, of which cereal grains supply the greatest percentage. Wheat, maize and rice together comprise at least 75% of the world’s grain production (Cordain 1999) The primary nutritious part of the cereal grain is the seed endosperm. Despite detailed knowledge of events that occur in angiosperm fertilization and endosperm formation, very little is known about the regulatory networks controlling the complex developmental and metabolic processes of cereal grain formation.

In cereal plants, double fertilization initiates the process of seed formation, in which one sperm nucleus fertilizes the egg cell in the embryo sac resulting in a diploid zygote, a second sperm nucleus fuses with two polar nuclei of the central cell to initiate the development of the triploid endosperm (Dumas and Mogensen 1993). The diploid zygote and the primary triploid nucleus enter separate developmental patterns to give rise to the embryo and the nutritive endosperm. The pathway leading to the formation of the endosperm from the triploid nucleus is a four stage process. (1) syncytial stage, where the primary triploid nucleus in the central cell undergoes a period of mitotic nuclear divisions without cytokinesis resulting in a large syncytium; (2) cellularization, a period during which cytokinesis separates the nuclei into discrete cells involving both anticlinal and periclinal divisions; (3) growth and differentiation, which results in distinct tissues namely starchy endosperm, basal transfer layer and aleurone and (4) maturation, an important process characterized by accumulation of storage reserves and the development of desiccation tolerance and dormancy (Becraft 2001, Olsen 2001)  .