Based on the frequency of maize- or teosinte-like plants in his cross, he argued that as few as five loci might be responsible for much of the phenotypic difference between maize and teosinte.
Later work by John Doebley et al. The two best-studied cases are the loci teosinte branched1 tb1 and teosinte glume architecture tga. Changes at tb1 are due to genetic alterations at distant regulatory sequences while critical changes at tga are likely to be due to amino-acid changes. Knowledge of these loci provides some of the best examples to date of how human selection for certain physical traits in maize has led to specific changes at the DNA level.
Many other genes, in addition to tb1 and tga1 , have played a role in domestication, however. The analysis of genetic diversity from whole-genome sequences of multiple maize and teosinte has identified nearly regions of the genome that show evidence of selection during domestication Hufford et al. Intriguingly, some of these regions do not contain genes, and many of the genes identified show differences in expression, pointing to the potentially important role of regulatory variation.
Overall, more than genes show reduced diversity due to the impact of selection. The modern diversity of inbred lines, ranging in their flowering time from 50 to days and in height from 3 to 15 feet tall, derives from maize landraces. Buckler, Holland and McMullen took advantage of this natural diversity to create a widely-used tool, the nested association mapping NAM panel, which consists of recombinant inbred populations see Glossary generated by crossing 25 diverse maize lines to the same recurrent parent McMullen et al.
This population is being used to identify the genes responsible for complex traits, such as flowering time Buckler et al. It appears that variation for most traits results from numerous genes that each have a small effect on a trait.
Maize differs in this regard from species that are self-pollinated, such as rice, sorghum and Arabidopsis , which frequently have fewer loci that produce large effects on traits Lin et al. Teosinte, as an out-crossing species, is similar to maize in this regard Weber et al.
Another powerful approach in maize that takes advantage of its diversity and history of outcrossing is that of genome wide association studies GWAS , which exploits ancient recombination events that have shuffled and reshuffled genes. GWAS looks for correlations between variation at individual markers and a trait, and has become an important complement to the use of experimental crosses.
By using detailed genetic and phenotypic information from the NAM line founders and by comparing this information to genotypic information obtained from their recombinant NAM progeny, we can begin to predict the phenotypic effects produced by the variants of many genes Wallace et al.
Using recently developed, high-throughput sequencing methods, a population of maize lines was genotyped with more than , single nucleotide polymorphic markers Romay et al. This density of marker information worked well for identifying the genetic basis of simple traits using GWAS, but more markers will be needed for analyzing complex traits.
The eventual goal of these efforts is to link genotypes with phenotypes for use in predictive breeding studies see Glossary. Predictive breeding will help breeders to create improved crops, by selecting alleles from different inbred maize lines to generate the combination of traits needed in a particular environment.
Today maize is one of the most important crops worldwide. As we try to increase yields, improve sustainability, and adapt maize to changing environmental and climatic conditions, we can take advantage of our understanding of the natural history of maize and its status as an important model organism. Future efforts at incorporating novel alleles into modern germplasm via selective breeding or transgenics, as well as developing predictive breeding models, will benefit from the history of research in maize, as well as its rich heritage of genetic diversity.
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication. This is an open-access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose.
The work is made available under the Creative Commons CC0 public domain dedication. Article citation count generated by polling the highest count across the following sources: Crossref , Scopus , PubMed Central. A better understanding of the natural history of model organisms will increase their value as model systems and also keep them at the forefront of research.
Essays on the wild lives of model organisms, from Arabidopsis to the zebrafish. Plants develop new organs to adjust their bodies to dynamic changes in the environment.
How independent organs achieve anisotropic shapes and polarities is poorly understood. To address this question, we constructed a mechano-biochemical model for Arabidopsis root meristem growth that integrates biologically plausible principles. Computer model simulations demonstrate how differential growth of neighboring tissues results in the initial symmetry-breaking leading to anisotropic root growth.
Furthermore, the root growth feeds back on a polar transport network of the growth regulator auxin. Model, predictions are in close agreement with in vivo patterns of anisotropic growth, auxin distribution, and cell polarity, as well as several root phenotypes caused by chemical, mechanical, or genetic perturbations.
Our study demonstrates that the combination of tissue mechanics and polar auxin transport organizes anisotropic root growth and cell polarities during organ outgrowth. Therefore, a mobile auxin signal transported through immobile cells drives polarity and growth mechanics to coordinate complex organ development.
Cited 37 Views 9, Annotations Open annotations. The current annotation count on this page is being calculated. Cite this article as: eLife ;4:e doi: Article Figures and data Abstract Introduction The lifecycle of maize Strengths as a model organism The position of maize in the grass family Identifying domestication genes Genetic diversity and analyzing complex traits Conclusion References Article and author information Metrics.
Figure 1. Download asset Open asset. Figure 2. Figure 3. The strengths of maize as a model organism. Separate male and female flowers that allow easily controlled crosses.
The availability of developmental series of meristems in the ear and tassel. Doebley J Stec A Genetic-analysis of the morphological differences between maize and teosinte. Doebley J Stec A Inheritance of the morphological differences between maize and teosinte: comparison of results for two F2 populations.
Emerson RA et al. Emerson RA Control of flowering in teosinte; shortday treatment brings early flowers. Hollick JB Paramutation: a trans-homolog interaction affecting heritable gene regulation Current Opinion in Plant Biology 15 — Iltis H Homeotic sexual translocations and the origin of maize Zea mays Poaceae : a new look at an old problem Economic Botony 54 :7— Figures, Tables, and Topics from this paper.
Citation Type. Has PDF. Publication Type. More Filters. Gametophytic cross-incompatibility in maize: resequencing the Ga1 locus.
Maize proteomics: An insight into the biology of an important cereal crop. View 1 excerpt, cites background. Previously regarded as an intriguing photosynthetic curiosity, the occurrence of C4 and Crassulacean acid metabolism CAM photosynthesis within a single organism has recently emerged as a source of … Expand. Somatic embryogenesis and plant regeneration of tropical maize genotypes. Over the past decades, advances in plant biotechnology have allowed the development of genetically modified maize varieties that have significantly impacted agricultural management and improved the … Expand.
Genetic and Genomic Toolbox of Zea mays. View 2 excerpts, cites background. Chemical Structure of RNA. Eukaryotic Genome Complexity. RNA Functions. Citation: Pray, L. Nature Education 1 1 Aa Aa Aa. Some of the most profound genetic discoveries have been made with the help of various model organisms that are favored by scientists for their widespread availability and ease of maintenance and proliferation.
One such model is Zea mays maize , particularly those plants that produce variably colored kernels. Because each kernel is an embryo produced from an individual fertilization , hundreds of offspring can be scored on a single ear, making maize an ideal organism for genetic analysis. Indeed, maize proved to be the perfect organism for the study of transposable elements TEs , also known as "jumping genes ," which were discovered during the middle part of the twentieth century by American scientist Barbara McClintock.
McClintock's work was revolutionary in that it suggested that an organism's genome is not a stationary entity, but rather is subject to alteration and rearrangement-a concept that was met with criticism from the scientific community at the time. However, the role of transposons eventually became widely appreciated, and McClintock was awarded the Nobel Prize in in recognition of this and her many other contributions to the field of genetics. McClintock and the Origins of Cytogenetics.
Figure 1. Figure 2: Variation in kernel phenotypes is used to study transposon behavior. Kernels on a maize ear show unstable phenotypes due to the interplay between a transposable element TE and a pigment gene. Plant transposable elements: where genetics meets genomics. Nature Reviews Genetics 3, All rights reserved. Expression of Ds in Maize. McClintock and the Theory of Epigenetics.
Beyond her discovery of TEs and her revolutionary cytogenetic research techniques, Barbara McClintock was also the first scientist to correctly speculate on the basic concept of epigenetics-or heritable changes in gene expression that are not caused by changes to DNA sequences.
Mainly, she recognized that genes can be expressed and silenced during mitosis in genetically identical cells. McClintock proposed this theory before the molecular structure of DNA and more than 40 years before the concept of epigenetics was formally studied, thereby further cementing her reputation as an innovator in her field. Barbara McClintock's discovery of transposable elements in Zea mays changed the way scientists think about genetic patterns of inheritance.
Although not widely accepted at the time of its discovery, McClintock's observation of the behavior of kernel color alleles was revolutionary in its proposition that genomic replication does not always follow a consistent pattern. Indeed, as a result of both autonomous and activator-controlled transposition at different stages of seed development, the genes of maize kernels are capable of producing a variety of coloration patterns. Today, McClintock is also recognized for her groundbreaking cytogenetic techniques, as well as her early speculations on the concept of epigenetics.
Thanks to these and other valuable contributions to the field, Barbara McClintock is rightly viewed as one of the pioneering figures in modern genetics. References and Recommended Reading Coe, E. Article History Close. Share Cancel. Revoke Cancel. Keywords Keywords for this Article. Save Cancel. Flag Inappropriate The Content is: Objectionable. Flag Content Cancel.
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