Maize and its closest wild relatives, the teosintes, differ strikingly in the morphology of their female inflorescences or ears. Despite their divergent morphologies, several studies indicate that ...some varieties of teosinte are cytologically indistinguishable from maize and capable of forming fully fertile hybrids with maize. Molecular analyses identified one form of teosinte (Zea mays ssp. parviglumis) as the progenitor of maize. Analyses of the inheritance of the morphological traits that distinguish maize and teosinte indicates that they are under the control of multiple genes and exhibit quantitative inheritance. Nevertheless, these analyses have also identified a few loci of large effect that appear to represent key innovations during maize domestication. Remaining challenges are to identify additional major and minor effect genes, the polymorphisms within these genes that control the phenotypes, and how the combination of the individual and epistatic effects of these genes transformed teosinte into maize.
Domestication is a tractable system for following evolutionary change. Under domestication, wild populations respond to shifting selective pressures, resulting in adaptation to the new ecological ...niche of cultivation. Owing to the important role of domesticated crops in human nutrition and agriculture, the ancestry and selection pressures transforming a wild plant into a domesticate have been extensively studied. In Zea mays, morphological, genetic and genomic studies have elucidated how a wild plant, the teosinte Z. mays subsp. parviglumis, was transformed into the domesticate Z. mays subsp. mays. Five major morphological differences distinguish these two subspecies, and careful genetic dissection has pinpointed the molecular changes responsible for several of these traits. But maize domestication was a consequence of more than just five genes, and regions throughout the genome contribute. The impacts of these additional regions are contingent on genetic background, both the interactions between alleles of a single gene and among alleles of the multiple genes that modulate phenotypes. Key genetic interactions include dominance relationships, epistatic interactions and pleiotropic constraint, including how these variants are connected in gene networks. Here, we review the role of gene interactions in generating the dramatic phenotypic evolution seen in the transition from teosinte to maize.
• Flowering time is a major determinant of the local adaptation of plants. Although numerous loci affecting flowering time have been mapped in maize, their underlying molecular mechanisms and roles ...in adaptation remain largely unknown.
• Here, we report the identification and characterization of MADS-box transcription factor ZmMADS69 that functions as a flowering activator through the ZmRap2.7-ZCN8 regulatory module and contributes to adaptation. We show that ZmMADS69 underlies a quantitative trait locus controlling the difference in flowering time between maize and its wild ancestor, teosinte. Maize ZmMADS69 allele is expressed at a higher level at floral transition and confers earlier flowering than the teosinte allele under long days and short days. Overexpression of ZmMADS69 causes early flowering, while a transposon insertion mutant of ZmMADS69 exhibits delayed flowering. ZmMADS69 shows pleiotropic effects for multiple traits of agronomic importance.
• ZmMADS69 functions upstream of the flowering repressor ZmRap2.7 to downregulate its expression, thereby relieving the repression of the florigen gene ZCN8 and causing early flowering. Population genetic analyses showed that ZmMADS69 was a target of selection and may have played an important role as maize spread from the tropics to temperate zones.
• Our findings provide important insights into the regulation and adaptation of flowering time.
Maize (Zea mays ssp. mays) was domesticated in southwestern Mexico ∼9,000 years ago from its wild ancestor, teosinte (Zea mays ssp. parviglumis) 1. From its center of origin, maize experienced a ...rapid range expansion and spread over 90° of latitude in the Americas 2–4, which required a novel flowering-time adaptation. ZEA CENTRORADIALIS 8 (ZCN8) is the maize florigen gene and has a central role in mediating flowering 5, 6. Here, we show that ZCN8 underlies a major quantitative trait locus (QTL) (qDTA8) for flowering time that was consistently detected in multiple maize-teosinte experimental populations. Through association analysis in a large diverse panel of maize inbred lines, we identified a SNP (SNP-1245) in the ZCN8 promoter that showed the strongest association with flowering time. SNP-1245 co-segregated with qDTA8 in maize-teosinte mapping populations. We demonstrate that SNP-1245 is associated with differential binding by the flowering activator ZmMADS1. SNP-1245 was a target of selection during early domestication, which drove the pre-existing early flowering allele to near fixation in maize. Interestingly, we detected an independent association block upstream of SNP-1245, wherein the early flowering allele that most likely originated from Zea mays ssp. mexicana introgressed into the early flowering haplotype of SNP-1245 and contributed to maize adaptation to northern high latitudes. Our study demonstrates how independent cis-regulatory variants at a gene can be selected at different evolutionary times for local adaptation, highlighting how complex cis-regulatory control mechanisms evolve. Finally, we propose a polygenic map for the pre-Columbian spread of maize throughout the Americas.
•ZCN8 underlies a major QTL for flowering time detected in maize-teosinte populations•Two independent cis-variants in the ZCN8 promoter affect maize flowering time•Two cis-variants in ZCN8 arose in a stepwise manner to enhance maize adaptation•The pre-Columbian spread of maize involved numerous loci with distinct features
Guo et al. show that two independently associated variants in the ZCN8 promoter control natural variation in maize flowering time. They demonstrate that the two cis-variants arose in a stepwise manner and played distinct roles in maize adaptation to higher latitudes. They finally propose a polygenic map for the pre-Columbian spread of maize.
Axillary branch suppression is a favorable trait bred into many domesticated crop plants including maize compared with its highly branched wild ancestor teosinte. Branch suppression in maize was ...achieved through selection of a gain of function allele of the teosinte branched1 (tb1) transcription factor that acts as a repressor of axillary bud growth. Previous work indicated that other loci may function epistatically with tb1 and may be responsible for some of its phenotypic effects. Here, we show that tb1 mediates axillary branch suppression through direct activation of the tassels replace upper ears1 (tru1) gene that encodes an ankyrin repeat domain protein containing a BTB/POZ motif necessary for protein–protein interactions. The expression of TRU1 and TB1 overlap in axillary buds, and TB1 binds to two locations in the tru1 gene as shown by chromatin immunoprecipitation and gel shifts. In addition, nucleotide diversity surveys indicate that tru1, like tb1, was a target of selection. In modern maize, TRU1 is highly expressed in the leaf trace vasculature of axillary internodes, while in teosinte, this expression is highly reduced or absent. This increase in TRU1 expression levels in modern maize is supported by comparisons of relative protein levels with teosinte as well as by quantitative measurements of mRNA levels. Hence, a major innovation in creating ideal maize plant architecture originated from ectopic overexpression of tru1 in axillary branches, a critical step in mediating the effects of domestication by tb1.
The progenitor of maize is Balsas teosinte (Zea mays subsp. parviglumis) which grows as a wild plant in the valley of the Balsas river in Mexico. Domestication, primarily targeting above-ground ...traits, has led to substantial changes in the plant's morphology and modern maize cultivars poorly resemble their wild ancestor. We examined the hypotheses that Balsas teosinte (accession PI 384071) has a) a different root system architecture and b) a structurally and functionally different rhizosphere microbial community than domesticated cultivars sweet corn (Zea mays subsp. mays accession PI 494083) and popping corn (Zea mays subsp. mays accession PI 542713). In a greenhouse experiment, five plants from each corn variety were grown in individual pots containing a Maury silt loam – perlite (2:1) mixture and grown to the V8 growth stage at which rhizosphere bacterial and fungal community structure was assessed using terminal restriction fragment length polymorphism and fatty acid methyl ester analysis. Functional characteristics of the rhizosphere were assayed by examining the potential activity of seven extracellular enzymes involved in carbon, nitrogen and phosphorus cycling. Root system architecture was characterized by root scans of sand grown plants at the V5 growth stage. Compared to the control the sweet corn rhizosphere had different bacterial and fungal community structure, decreased fungal diversity and increased bacterial abundance. Teosinte caused a significant change in the rhizosphere bacterial and fungal community structure and increased bacterial abundance, but no significant decrease in bacterial or fungal diversity where the former was found to be significantly greater than in the sweet corn rhizosphere. Popping corn did not trigger significant changes in the bacterial or fungal diversity and bacterial abundance in the soil. The individual popping corn plants changed the bacterial and fungal communities in different directions and the overall effect on community structure was significant, but small. Of the enzymes analyzed, potential N-acetylglucosaminidase (NAG) activity was found to contributed most to the differentiation of teosinte rhizosphere samples from the other corn varieties. The teosinte root system had proportionally more very fine (diameter < 0.03 mm) roots than popping corn and sweet corn and it developed the highest root to shoot dry weight ratio, followed by popping corn. Sweet corn had significantly lower average root diameter than popping corn and teosinte and grew proportionally the least below-ground dry mass. The results allude to functional and structural differences in the rhizosphere microbial communities of the corn varieties that, with additional research, could lead to useful discoveries on how corn domestication has altered rhizosphere processes and how plant genotype influences nutrient cycling.
•Rhizosphere processes of ancestral and domesticated corn varieties were assessed.•We examine microbe community structure, enzyme activity and root system architecture.•Influence of corn varieties on rhizosphere processes was detectable but subtle.•Sweet corn had the most influence followed by teosinte and popping corn.•Findings could be used to screen genotypes for beneficial rhizosphere traits.
Domesticated plants are assumed to have weakened chemical defenses. We argue, however, that artificial selection will have maintained defense traits against specialized herbivores that have coexisted ...with the crops throughout their domestication.
We assessed the performance of eight species of insect herbivores from three feeding guilds on six European maize lines and six populations of their wild ancestor, teosinte. A metabolomics approach was used in an attempt to identify compounds responsible for observed differences in insect performance.
Insects consistently performed better on maize than on teosinte. As hypothesized, this difference was greater for generalist herbivores that are normally not found on teosinte. We also found clear differences in defense metabolites among the different genotypes, but none that consistently correlated with differences in performance. Concentrations of benzoxazinoids, the main chemical defense in maize, tended to be higher in leaves of teosinte, but the reverse was true for the roots.
It appears that chemical defenses that target specialized insects are still present at higher concentrations in cultivated maize than compounds that are more effective against generalists. These weakened broad-spectrum defenses in crops may explain the successes of novel pests.
The complex evolutionary history of maize (Zea mays L. ssp. mays) has been clarified with genomic-level data from modern landraces and wild teosinte grasses 1, 2, augmenting archaeological findings ...that suggest domestication occurred between 10,000 and 6,250 years ago in southern Mexico 3, 4. Maize rapidly evolved under human selection, leading to conspicuous phenotypic transformations, as well as adaptations to varied environments 5. Still, many questions about the domestication process remain unanswered because modern specimens do not represent the full range of past diversity due to abandonment of unproductive lineages, genetic drift, on-going natural selection, and recent breeding activity. To more fully understand the history and spread of maize, we characterized the draft genome of a 5,310-year-old archaeological cob excavated in the Tehuacan Valley of Mexico. We compare this ancient sample against a reference panel of modern landraces and teosinte grasses using D statistics, model-based clustering algorithms, and multidimensional scaling analyses, demonstrating the specimen derives from the same source population that gave rise to modern maize. We find that 5,310 years ago, maize in the Tehuacan Valley was on the whole genetically closer to modern maize than to its wild counterpart. However, many genes associated with key domestication traits existed in the ancestral state, sharply contrasting with the ubiquity of derived alleles in living landraces. These findings suggest much of the evolution during domestication may have been gradual and encourage further paleogenomic research to address provocative questions about the world’s most produced cereal.
•Researchers characterized genome of a 5,310-year-old maize cob•The ancient maize genome is a basal lineage equally related to modern landraces•There is genetic evidence of naked kernels 5,310 years ago in Tehuacan, Mexico•Human selection on maize domestication traits occurred as a gradual process
Ramos-Madrigal et al. sequence the genome of 5,310-year-old maize cob, which represents a basal lineage equally related to all modern varieties. They provide an in-depth genomic characterization of maize at an early point during its evolution as a domesticate, suggesting that human selection occurred as a gradual process.
Gluten-free products present huge advantages for individuals with gluten intolerance or celiac disease. The most influential strategy to develop a product comparable to wheat-containing gluten ...products is to promote its nutritional and sensorial attributes. Recently, rice flour and teosinte flour were used to develop gluten-free bread. As a result, this work aimed to compare the physical/technological attributes of bread made with rice flour and teosinte flour with corn fiber fortification and examine consumer acceptance and purchase intent. An extreme vertices mixture design decided that a teosinte flour (43.4%), high protein white rice flour (55%), and high protein brown rice flour (1.6%) ratio of gluten-free flour mixture for bread was best based on the sensory attributes utilized for the desirability function methodology. After optimizing the gluten-free flour mixture, the bread was fortified with corn fiber under 1.7 g and 3.8 g per serving, and it was evaluated to examine its physical/technological attributes, consumer perception, liking, emotions, and purchase intent. Incorporating fiber into gluten-free bread impacted the color and texture, giving lighter and yellower colors with a firmer texture. Likewise, concerning health benefit claims, gluten-free bread with fiber claims only improves the purchase intent and overall liking of bread containing 1.7 g per serving of fiber. The flavor attribute was the main driver for consumers’ purchase decisions. This product could be beneficial for consumers who are seeking fiber in their diet.
Regulation of plant height and stem elongation has contributed significantly to improvement of cereal productivity by reducing lodging and improving distribution of assimilates to the inflorescence ...and grain. In wheat, genetic control of height has been largely contributed by the Reduced height-1 alleles that confer gibberellin insensitivity; the beneficial effects of these alleles are associated with less favourable effects involving seedling emergence, grain quality, and inflorescence architecture that have driven new research investigating genetic variation of stem growth. Here, we show that TEOSINTE BRANCHED1 (TB1) regulates height of wheat, with TB1 being expressed at low levels in nodes of the main culm prior to elongation, and increased dosage of TB1 restricting elongation of stem internodes. The effect of TB1 on stem growth is not accompanied by poor seedling emergence, as transgenic lines with increased activity of TB1 form longer coleoptiles than null transgenic controls. Analysis of height in a multiparent mapping population also showed that allelic variation for TB1 on the B genome influences height, with plants containing the variant TB-B1b allele being taller than those with the wild-type TB-B1a allele. Our results show that TB1 restricts height and stem elongation in wheat, suggesting that variant alleles that alter the expression or function of TB1 could be used as a new source of genetic diversity for optimizing architecture of wheat in breeding programmes.
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