As one of the world's most important crops, maize (corn) needs little introduction. What is less well appreciated is the story of its remarkable transformation (Figure 1). Genetic data point to the tropical Balsas river valley in Mexico as the site where maize (Zea mays ssp. mays) was domesticated from teosinte (Zea mays ssp. parviglumis) (Matsuoka et al., 2002; van Heerwaarden et al., 2011). Archeological data support this location and also suggest that squash may have been domesticated at the same time (Piperno et al., 2009). Some think maize was first collected for the fermentable sugars in its stalk (Iltis, 2000; Smalley and Blake, 2003), but more likely it was for the storable starch in its seed.

Figure 1

Download asset Open asset

The word teosinte is derived from ‘teocintli’—‘teotl’ meaning sacred and ‘cintli’ meaning dried ear of corn—from the indigenous Nahuatl language. We use the word teosinte to refer to all the wild species of Zea that are native to Mexico and Central America. Teosinte sows its seeds widely. In addition to dispersing pollen in the wind, the kernels fall from the plant and, if eaten, are carried to other locations in fecal matter, thanks to the indigestible fruitcase (see Box 1 for a glossary of specialist terms used in this article). The domestication of maize kept the wind-born pollen of teosinte, but changed other traits, improving its utility for human consumption (Doebley, 2004). The teosinte fruitcase, full of silica and lignin, became softer (Figure 1C), allowing humans to grind its kernels for food. The branch holding the kernels (cob) grew in girth, increasing the kernel row number from 2 to 20, or more (Figure 1D). Kernels no longer self-dispersed but were held tight on the cob, requiring the intervention of humans to sow seeds. Finally, the long branches shortened, but kept the leaves along the branch. These ‘husk leaves’ keep birds, insects and other pests from eating the kernels.

From the Balsas region of Mexico, maize spread north and south (Matsuoka et al., 2002), adapting to very different environmental conditions. In a testament to its adaptability, maize is now found growing across a wider area than any other major crop (Figure 2). Cobs of corn found in archeological sites suggest that major morphological changes had occurred by 6500 years ago (Piperno and Flannery, 2001). Pollen flow between domesticated maize and other teosinte taxa contributed to some of its diversification (van Heerwaarden et al., 2011), and local adaptation and trade continue to shape maize genetic diversity (Mercer et al., 2008; Ruiz Corral et al., 2008). Maize varieties in Mexico can often be distinguished by kernel or cob traits (Vielle-Calzada and Padilla, 2009) but genetic diversity within these open-pollinated populations remains high (Pressoir and Berthaud, 2004).

Figure 2

Download asset Open asset

Darwin was the first to recognize inbreeding depression (see Glossary) in maize, a critical component of maize breeding. He noted a reduced size in self-pollinated corn and the improved size and vigor, or heterosis, of cross-pollinated corn (Darwin, 1876). His observations were extended by George Harrison Shull in 1908, who made inbreds by self-pollinating maize plants for multiple generations before crossing them together to make hybrids (Shull, 1908). Today, of course, hybrid maize is the predominant form grown in industrial agriculture (Duvick, 2001), with traditional open-pollinated landraces (see Glossary) primarily limited to small scale or subsistence farming.

Teosinte is sensitive to day length and only makes flowers when days are short (Emerson, 1924). An important step in breeding maize for higher latitudes involved overriding this environmental control, creating maize plants that flower independently of day length. The maize shoot apical meristem (see Glossary) initiates a genetically determined number of leaves before it transitions to become the male reproductive structure, known as the tassel. Buds are found in the axils (see Glossary) of most leaves—the lower buds become tillers, which are long branches, resembling the main stem. The buds above the tillers will develop into the ears, which hold the kernels. During early development, the ear and tassel primordia appear similar to each other (Figure 3A,B). Sex determination genes initiate a program that blocks development of female reproductive parts in the male flowers of the tassel and male reproductive parts in the female flowers of the ear (Cheng et al., 1983). Interestingly, the tassel of a tiller is often partially feminized. While teosinte plants have multiple tillers, ensuring a supply of pollen over many days, modern maize often has a single tassel and lacks tillers entirely. Maize hybrids are created by planting two distinct inbreds in alternate rows and detasseling one inbred, ensuring that the ears on detasseled plants are cross-pollinated and thus hybrid.

Figure 3

Download asset Open asset

As with other flowering plants, the male sperm is carried in the pollen. Following meiosis, the microspore undergoes two mitotic divisions, generating two sperm cells contained within a vegetative cell (see Glossary). The vegetative nucleus does the work of bringing the sperm cells to the female egg. The pollen germinates on silks, the extended pistils (see Glossary) of the female flower, and grows a tube inside the silk. Once the pollen tube reaches the plant's ovule, one sperm will fertilize the haploid egg cell, creating the diploid embryo, and the other sperm will fertilize the central cell of the female gametophyte, which has two polar nuclei (see Glossary). The resulting triploid cell develops into the endosperm, a sacrificial tissue that feeds the growing embryo.

Once the kernel, containing the double fertilization event, matures, it can be planted or stored for years in a dry state. The root emerges first, growing towards gravity. The shoot grows upward, supported by the nutrients of the endosperm (Figure 3C). Maize is a monocotyledonous plant, meaning it produces one embryonic leaf (as compared to another model plant Arabidopsis thaliana, which is a dicotyledonous plant). The cotyledon equivalent for maize is the coleoptile, which is connected to the nutritive scutellum (see Glossary). Inside the tubular coleoptile are sequentially younger leaves that arise from a shoot apical meristem.

Geneticists began collecting, describing and distributing maize mutants in the early 1900's (see references in Emerson et al., 1935). They took advantage of a number of features that make maize a valuable resource for genetic research (Box 2). Dozens of genes affect the texture of the endosperm and the color of its outermost layer, the aleurone, providing easily visible and eye-catching information about the genotype of the next generation. The large, distinctive chromosomes of maize further paved the way for a number of major discoveries, including linking genetic recombination to physical exchange of chromosomal segments (Creighton and McClintock, 1931). The copious amounts of pollen maize plants produce can be easily gathered and mutagenized with chemicals to create new mutant plants, allowing researchers to easily screen for even lethal mutations (Neuffer, 1993; Candela and Hake, 2008). Transposable elements (see Glossary), first described by Barbara McClintock (McClintock, 1950), continue to be an important tool for cloning genes based on mutant phenotype, and their use has provided novel insights into epigenetics (Lisch, 2012), such as the relationship between transposon activity and DNA methylation (Chandler and Walbot, 1986).

Maize and teosinte are members of the grass family Poaceae, which includes more than 10,000 species (Kellogg, 1998), including the major cereals, such as wheat and rice. The subfamily that includes Zea is Panicoideae (3236 species), which also includes C4 energy crops (see Glossary) such as switchgrass, sorghum, miscanthus and the recently sequenced model, Setaria (Grass Phylogeny Working Group II, 2012). Wheat, barley, and the model Brachypodium are in the Pooideae subfamily (3850 species), while rice, a well-studied model, as well as an important crop, is in the Ehrartoideae (111 species) (Grass Phylogeny Working Group II, 2012). The latter two subfamilies contain only C3 grasses.

Despite the difference of more than 60 million years of evolution, studies of grass genomes have revealed that significant portions of their chromosomes share the same gene arrangement (Moore et al., 1995). This discovery provides an opportunity to isolate genes based on common positions of shared markers. With the ever-increasing number of sequenced grass genomes, such as rice, sorghum, Brachypodium, Setaria and maize (https://genomevolution.org/wiki/index.php/Sequenced_plant_genomes#Grasses), researchers can now take advantage of comparative genomics to identify orthologous genes and regulatory elements that are likely to be important for biological processes (Lin et al., 2012).

George Beadle was the first to cross maize with teosinte and examine the F2 progeny (Beadle 1972). 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. found quantitative trait loci (QTL; see Glossary) consistent with this idea (Doebley and Stec, 1991, 1993), and careful genetic analysis of these regions allowed Doebley's group to dissect some of these QTL down to the responsible genes. The two best-studied cases are the loci teosinte branched1 (tb1) and teosinte glume architecture (tga). tb1 is responsible for the shortening and feminization of the axillary branches in domesticated maize (Doebley et al., 1997; Studer et al., 2011), while tga is responsible for the hardened fruitcase of teosinte (Wang et al., 2005). 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 500 regions of the genome that show evidence of selection during domestication (Hufford et al., 2012). 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 3000 genes show reduced diversity due to the impact of selection. In spite of this strong selection, maize landraces still retain more than 80% of the diversity found in teosinte, and it should be possible to identify potentially useful genetic diversity in landraces or teosinte while maintaining the key genetic contributors to improved maize.

The modern diversity of inbred lines, ranging in their flowering time from 50 to 120 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 5000 recombinant inbred populations (see Glossary) generated by crossing 25 diverse maize lines to the same recurrent parent (McMullen et al., 2009). This population is being used to identify the genes responsible for complex traits, such as flowering time (Buckler et al., 2009), plant architecture (Brown et al., 2011; Tian et al., 2011), and resistance to pests (Kump et al., 2011; Poland et al., 2011). 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., 1995; Salome et al., 2011; Huang et al., 2012). Teosinte, as an out-crossing species, is similar to maize in this regard (Weber et al., 2008).

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., 2014). Other collections of maize inbred lines are also available for GWAS studies (Flint-Garcia et al., 2005). Using recently developed, high-throughput sequencing methods, a population of 2815 maize lines was genotyped with more than 600,000 single nucleotide polymorphic markers (Romay et al., 2013). 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.

1. 1. Birchler JA

   (2014) Engineered minichromosomes in plants

   Current Opinion in Plant Biology 19:76–80.

   https://doi.org/10.1016/j.pbi.2014.05.009

   • Google Scholar
2. 1. Birchler JA
   2. Hart JR

   (1987)

   Interaction of endosperm size factors in maize

   Genetics 117:309–317.

   • Google Scholar
3. 1. Brown PJ
   2. Upadyayula N
   3. Mahone GS
   4. Tian F
   5. Bradbury PJ
   6. Myles S
   7. Holland JB
   8. Flint-Garcia S
   9. McMullen MD
   10. Buckler ES
   11. Rocheford TR

   (2011) Distinct genetic architectures for male and female inflorescence traits of maize

   PLOS Genetics 7:e1002383.

   https://doi.org/10.1371/journal.pgen.1002383

   • Google Scholar
4. 1. Buckler ES
   2. Holland JB
   3. Bradbury PJ
   4. Acharya CB
   5. Brown PJ
   6. Browne C
   7. Ersoz E
   8. Flint-Garcia S
   9. Garcia A
   10. Glaubitz JC
   11. Goodman MM
   12. Harjes C
   13. Guill K
   14. Kroon DE
   15. Larsson S
   16. Lepak NK
   17. Li H
   18. Mitchell SE
   19. Pressoir G
   20. Peiffer JA
   21. Rosas MO
   22. Rocheford TR
   23. Romay MC
   24. Romero S
   25. Salvo S
   26. Sanchez Villeda H
   27. da Silva HS
   28. Sun Q
   29. Tian F
   30. Upadyayula N
   31. Ware D
   32. Yates H
   33. Yu J
   34. Zhang Z
   35. Kresovich S
   36. McMullen MD

   (2009) The genetic architecture of maize flowering time

   Science 325:714–718.

   https://doi.org/10.1126/science.1174276

   • Google Scholar
5. 1. Candela H
   2. Hake S

   (2008) The art and design of genetic screens: maize

   Nature Reviews Genetics 9:192–203.

   https://doi.org/10.1038/nrg2291

   • Google Scholar
6. 1. Chandler VL
   2. Walbot V

   (1986) DNA modification of a maize transposable element correlates with loss of activity

   Proceedings of the National Academy of Sciences of USA 83:1767–1771.

   https://doi.org/10.1073/pnas.83.6.1767

   • Google Scholar
7. 1. Cheng PC
   2. Greyson RI
   3. Walden DB

   (1983) Organ initiation and the development of unisexual flowers in the tassel and ear of Zea mays

   American Journal of Botany 70:450–462.

   https://doi.org/10.2307/2443252

   • Google Scholar
8. 1. Creighton HB
   2. McClintock B

   (1931) A correlation of cytological and genetical crossing-over in Zea Mays

   Proceedings of the National Academy of Sciences of USA 17:492–497.

   https://doi.org/10.1073/pnas.17.8.492

   • Google Scholar
9. Book

   1. Darwin C

   (1876)

   The Effects of Cross and Self Fertilization in the Vegetable Kingdom

   John Murray.

   • Google Scholar
10. 1. Doebley J
    2. Stec A

    (1991)

    Genetic-analysis of the morphological differences between maize and teosinte

    Genetics 129:285–295.

    • Google Scholar
11. 1. Doebley J
    2. Stec A

    (1993)

    Inheritance of the morphological differences between maize and teosinte: comparison of results for two F2 populations

    Genetics 134:559–570.

    • Google Scholar
12. 1. Doebley J
    2. Stec A
    3. Hubbard L

    (1997) The evolution of apical dominance in maize

    Nature 386:485–488.

    https://doi.org/10.1038/386485a0

    • Google Scholar
13. 1. Doebley J

    (2004) The genetics of maize evolution

    Annual Review of Genetics 38:37–59.

    https://doi.org/10.1146/annurev.genet.38.072902.092425

    • Google Scholar
14. 1. Duvick DN

    (2001) Biotechnology in the 1930s: the development of hybrid maize

    Nature Reviews Genetics 2:69–74.

    https://doi.org/10.1038/35047587

    • Google Scholar
15. 1. Emerson RA

    et al. (1935)

    A summary of linkage studies in maize

    Cornell University Agricultural Experiment Station Memoir 180:1–83.

    • Google Scholar
16. 1. Emerson RA

    (1924)

    Control of flowering in teosinte; shortday treatment brings early flowers

    Journal of Heredity 15:41–49.

    • Google Scholar
17. 1. Flint-Garcia SA
    2. Thuillet AC
    3. Yu J
    4. Pressoir G
    5. Romero SM
    6. Mitchell SE
    7. Doebley J
    8. Kresovich S
    9. Goodman MM
    10. Buckler ES

    (2005) Maize association population: a high-resolution platform for quantitative trait locus dissection

    The Plant Journal 44:1054–1064.

    https://doi.org/10.1111/j.1365-313X.2005.02591.x

    • Google Scholar
18. 1. Hollick JB

    (2012) Paramutation: a trans-homolog interaction affecting heritable gene regulation

    Current Opinion in Plant Biology 15:536–543.

    https://doi.org/10.1016/j.pbi.2012.09.003

    • Google Scholar
19. 1. Huang X
    2. Zhao Y
    3. Wei X
    4. Li C
    5. Wang A
    6. Zhao Q
    7. Li W
    8. Guo Y
    9. Deng L
    10. Zhu C
    11. Fan D
    12. Lu Y
    13. Weng Q
    14. Liu K
    15. Zhou T
    16. Jing Y
    17. Si L
    18. Dong G
    19. Huang T
    20. Lu T
    21. Feng Q
    22. Qian Q
    23. Li J
    24. Han B

    (2012) Genome-wide association study of flowering time and grain yield traits in a worldwide collection of rice germplasm

    Nature Genetics 44:32–39.

    https://doi.org/10.1038/ng.1018

    • Google Scholar
20. 1. Hufford MB
    2. Xu X
    3. van Heerwaarden J
    4. Pyhäjärvi T
    5. Chia JM
    6. Cartwright RA
    7. Elshire RJ
    8. Glaubitz JC
    9. Guill KE
    10. Kaeppler SM
    11. Lai J
    12. Morrell PL
    13. Shannon LM
    14. Song C
    15. Springer NM
    16. Swanson-Wagner RA
    17. Tiffin P
    18. Wang J
    19. Zhang G
    20. Doebley J
    21. McMullen MD
    22. Ware D
    23. Buckler ES
    24. Yang S
    25. Ross-Ibarra J

    (2012) Comparative population genomics of maize domestication and improvement

    Nature Genetics 44:808–811.

    https://doi.org/10.1038/ng.2309

    • Google Scholar
21. 1. Iltis H

    (2000) Homeotic sexual translocations and the origin of maize (Zea mays Poaceae): a new look at an old problem

    Economic Botony 54:7–42.

    https://doi.org/10.1007/BF02866598

    • Google Scholar
22. 1. Kellogg EA

    (1998) Relationships of cereal crops and other grasses

    Proceedings of the National Academy of Sciences of USA 95:2005–2010.

    https://doi.org/10.1073/pnas.95.5.2005

    • Google Scholar
23. 1. Kump KL
    2. Bradbury PJ
    3. Wisser RJ
    4. Buckler ES
    5. Belcher AR
    6. Oropeza-Rosas MA
    7. Zwonitzer JC
    8. Kresovich S
    9. McMullen MD
    10. Ware D
    11. Balint-Kurti PJ
    12. Holland JB

    (2011) Genome-wide association study of quantitative resistance to southern leaf blight in the maize nested association mapping population

    Nature Genetics 43:163–168.

    https://doi.org/10.1038/ng.747

    • Google Scholar
24. 1. Lin YR
    2. Schertz KF
    3. Paterson AH

    (1995)

    Comparative analysis of QTLs affecting plant height and maturity across the Poaceae, in reference to an interspecific sorghum population

    Genetics 141:391–411.

    • Google Scholar
25. 1. Lin Z
    2. Li X
    3. Shannon LM
    4. Yeh CT
    5. Wang ML
    6. Bai G
    7. Peng Z
    8. Li J
    9. Trick HN
    10. Clemente TE
    11. Doebley J
    12. Schnable PS
    13. Tuinstra MR
    14. Tesso TT
    15. White F
    16. Yu J

    (2012) Parallel domestication of the Shattering1 genes in cereals

    Nature Genetics 44:720–724.

    https://doi.org/10.1038/ng.2281

    • Google Scholar
26. 1. Lisch D

    (2012) Regulation of transposable elements in maize

    Current Opinion in Plant Biology 15:511–516.

    https://doi.org/10.1016/j.pbi.2012.07.001

    • Google Scholar
27. 1. Matsuoka Y
    2. Vigouroux Y
    3. Goodman MM
    4. Sanchez GJ
    5. Buckler E
    6. Doebley J

    (2002) A single domestication for maize shown by multilocus microsatellite genotyping

    Proceedings of the National Academy of Sciences of USA 99:6080–6084.

    https://doi.org/10.1073/pnas.052125199

    • Google Scholar
28. 1. McClintock B

    (1950) The origin and behavior of mutable loci in maize

    Proceedings of the National Academy of Sciences of USA 36:344–355.

    https://doi.org/10.1073/pnas.36.6.344

    • Google Scholar
29. 1. McMullen MD
    2. Kresovich S
    3. Villeda HS
    4. Bradbury P
    5. Li H
    6. Sun Q
    7. Flint-Garcia S
    8. Thornsberry J
    9. Acharya C
    10. Bottoms C
    11. Brown P
    12. Browne C
    13. Eller M
    14. Guill K
    15. Harjes C
    16. Kroon D
    17. Lepak N
    18. Mitchell SE
    19. Peterson B
    20. Pressoir G
    21. Romero S
    22. Oropeza Rosas M
    23. Salvo S
    24. Yates H
    25. Hanson M
    26. Jones E
    27. Smith S
    28. Glaubitz JC
    29. Goodman M
    30. Ware D
    31. Holland JB
    32. Buckler ES

    (2009) Genetic properties of the maize nested association mapping population

    Science 325:737–740.

    https://doi.org/10.1126/science.1174320

    • Google Scholar
30. 1. Mercer K
    2. Martínez-Vásquez Á
    3. Perales HR

    (2008) Asymmetrical local adaptation of maize landraces along an altitudinal gradient

    Evolutionary Applications 1:489–500.

    https://doi.org/10.1111/j.1752-4571.2008.00038.x

    • Google Scholar
31. 1. Monfreda C

    et al. (2008) Farming the planet: 2. Geographic distribution of crop areas, yields, physiological types, and net primary production in the year 2000

    Global Biogeochemical Cycles 22:GB1022.

    https://doi.org/10.1029/2007GB002947

    • Google Scholar
32. 1. Moore G
    2. Devos KM
    3. Wang Z
    4. Gale MD

    (1995) Cereal genome evolution - grasses, line up and form a Circle

    Current Biology 7:737–739.

    https://doi.org/10.1016/S0960-9822(95)00148-5

    • Google Scholar
33. 1. Nannas NJ
    2. Dawe RK

    (2015)

    Genetics and genomic toolbo of Zea mays

    Genetics 199:655–699.

    • Google Scholar
34. Book

    1. Neuffer MG

    (1993)

    Mutagenesis

    In: Freeling M, Walbot V, editors. The Maize Handbook. Springer-Verlag. pp. 212–219.

    • Google Scholar
35. 1. Piperno DR
    2. Flannery KV

    (2001) The earliest archaeological maize (Zea mays L.) from highland Mexico: new accelerator mass spectrometry dates and their implications

    Proceedings of the National Academy of Sciences of USA 98:2101–2103.

    https://doi.org/10.1073/pnas.98.4.2101

    • Google Scholar
36. 1. Piperno DR
    2. Ranere AJ
    3. Holst I
    4. Iriarte J
    5. Dickau R

    (2009) Starch grain and phytolith evidence for early ninth millennium B.P. maize from the Central Balsas River Valley, Mexico

    Proceedings of the National Academy of Sciences of USA 106:5019–5024.

    https://doi.org/10.1073/pnas.0812525106

    • Google Scholar
37. 1. Poland JA
    2. Bradbury PJ
    3. Buckler ES
    4. Nelson RJ

    (2011) Genome-wide nested association mapping of quantitative resistance to northern leaf blight in maize

    Proceedings of the National Academy of Sciences of USA 108:6893–6898.

    https://doi.org/10.1073/pnas.1010894108

    • Google Scholar
38. 1. Pressoir G
    2. Berthaud J

    (2004) Population structure and strong divergent selection shape phenotypic diversification in maize landraces

    Heredity 92:95–101.

    https://doi.org/10.1038/sj.hdy.6800388

    • Google Scholar
39. 1. Romay MC
    2. Millard MJ
    3. Glaubitz JC
    4. Peiffer JA
    5. Swarts KL
    6. Casstevens TM
    7. Elshire RJ
    8. Acharya CB
    9. Mitchell SE
    10. Flint-Garcia SA
    11. McMullen MD
    12. Holland JB
    13. Buckler ES
    14. Gardner CA

    (2013) Comprehensive genotyping of the USA national maize inbred seed bank

    Genome Biology 14:R55.

    https://doi.org/10.1186/gb-2013-14-6-r55

    • Google Scholar
40. 1. Ruiz Corral JA

    et al. (2008) Climatic adaptation and ecological descriptors of 42 Mexican maize races

    Crop Science 48:1502–1512.

    https://doi.org/10.2135/cropsci2007.09.0518

    • Google Scholar
41. 1. Salome PA
    2. Bomblies K
    3. Laitinen RA
    4. Yant L
    5. Mott R
    6. Weigel D

    (2011) Genetic architecture of flowering-time variation in Arabidopsis thaliana

    Genetics 188:421–433.

    https://doi.org/10.1534/genetics.111.126607

    • Google Scholar
42. 1. Shull G

    (1908)

    The composition of a field of maize

    Rep Am Breeders Assoc 4:296–301.

    • Google Scholar
43. 1. Smalley S
    2. Blake M

    (2003) Sweet beginnings: stalk sugar and the domestication of maize

    Current Anthropology 44:675–703.

    https://doi.org/10.1086/377664

    • Google Scholar
44. 1. Studer A
    2. Zhao Q
    3. Ross-Ibarra J
    4. Doebley J

    (2011) Identification of a functional transposon insertion in the maize domestication gene tb1

    Nature Genetics 43:1160–1166.

    https://doi.org/10.1038/ng.942

    • Google Scholar
45. 1. Tian F
    2. Bradbury PJ
    3. Brown PJ
    4. Hung H
    5. Sun Q
    6. Flint-Garcia S
    7. Rocheford TR
    8. McMullen MD
    9. Holland JB
    10. Buckler ES

    (2011) Genome-wide association study of leaf architecture in the maize nested association mapping population

    Nature Genetics 43:159–162.

    https://doi.org/10.1038/ng.746

    • Google Scholar
46. 1. van Heerwaarden J
    2. Doebley J
    3. Briggs WH
    4. Glaubitz JC
    5. Goodman MM
    6. de Jesus Sanchez Gonzalez J
    7. Ross-Ibarra J

    (2011) Genetic signals of origin, spread, and introgression in a large sample of maize landraces

    Proceedings of the National Academy of Sciences of USA 108:1088–1092.

    https://doi.org/10.1073/pnas.1013011108

    • Google Scholar
47. Book

    1. Vielle-Calzada JP
    2. Padilla J

    (2009)

    The Mexican Landraces: Description, Classification and Diversity

    Springer.

    • Google Scholar
48. 1. Wallace JG
    2. Larsson SJ
    3. Buckler ES

    (2014) Entering the second century of maize quantitative genetics

    Heredity 112:30–38.

    https://doi.org/10.1038/hdy.2013.6

    • Google Scholar
49. 1. Wang H
    2. Nussbaum-Wagler T
    3. Li B
    4. Zhao Q
    5. Vigouroux Y
    6. Faller M
    7. Bomblies K
    8. Lukens L
    9. Doebley JF

    (2005) The origin of the naked grains of maize

    Nature 436:714–719.

    https://doi.org/10.1038/nature03863

    • Google Scholar
50. 1. Weber AL
    2. Briggs WH
    3. Rucker J
    4. Baltazar BM
    5. de Jesús Sánchez-Gonzalez J
    6. Feng P
    7. Buckler ES
    8. Doebley J

    (2008) The genetic architecture of complex traits in teosinte (Zea mays ssp. parviglumis): new evidence from association mapping

    Genetics 180:1221–1232.

    https://doi.org/10.1534/genetics.108.090134

    • Google Scholar

Author details

1. Sarah Hake

   Plant Gene Expression Center, US Department of Agriculture-Agriculture Research Service, Albany, United States

   Contribution

   SH, Conception and design, Drafting or revising the article

   For correspondence

   hake@berkeley.edu

   Competing interests

   The authors declare that no competing interests exist.

2. Jeffrey Ross-Ibarra

   Department of Plant Sciences, Center for Population Biology and Genome Center, University of California, Davis, Davis, United States

   Contribution

   JR-I, Drafting or revising the article

   Competing interests

   The authors declare that no competing interests exist.

• 10,308

  views

• 1,941

  downloads

• 88

  citations

Views, downloads and citations are aggregated across all versions of this paper published by eLife.