Perennial Teosinte Research Articles

A teosinte-derived allele of ZmSC improves salt tolerance in maize.

Maize, a salt-sensitive crop, frequently suffers severe yield losses due to soil salinization. Enhancing salt tolerance in maize is crucial for maintaining yield stability. To address this, we developed an introgression line (IL76) through introgressive hybridization between maize wild relatives Zea perennis, Tripsacum dactyloides, and inbred Zheng58, utilizing the tri-species hybrid MTP as a genetic bridge. Previously, genetic variation analysis identified a polymorphic marker on Zm00001eb244520 (designated as ZmSC), which encodes a vesicle-sorting protein described as a salt-tolerant protein in the NCBI database. To characterize the identified polymorphic marker, we employed gene cloning and homologous cloning techniques. Gene cloning analysis revealed a non-synonymous mutation atthe 1847th base of ZmSCIL76 , where a guanine-to-cytosine substitution resultedin the mutation of serine to threonine at the 119th amino acid sequence (using ZmSCZ58 as the reference sequence). Moreover, homologous cloning demonstrated that the variation site derived from Z. perennis. Functional analyses showed that transgenic Arabidopsis lines overexpressing ZmSCZ58 exhibited significant reductions in leaf number, root length, and pod number, alongside suppression of the expression of genes in the SOS and CDPK pathways associated with Ca2+ signaling. Similarly, fission yeast strains expressing ZmSCZ58 displayed inhibited growth. In contrast, the ZmSCIL76 allele from Z. perennis alleviated these negative effects in both Arabidopsis and yeast, with the lines overexpressing ZmSCIL76 exhibiting significantly higher abscisic acid (ABA) content compared to those overexpressing ZmSCZ58 . Our findings suggest that ZmSC negatively regulates salt tolerance in maize by suppressing downstream gene expression associated with Ca2+ signaling in the CDPK and SOS pathways. The ZmSCIL76 allele from Z. perennis, however, can mitigate this negative regulatory effect. These results provide valuable insights and genetic resources for future maize salt tolerance breeding programs.

Unlocking the hidden potential of Mexican teosinte seeds: revealing plant growth-promoting bacterial and fungal biocontrol agents.

The bacterial component of plant holobiont maintains valuable interactions that contribute to plants' growth, adaptation, stress tolerance, and antagonism to some phytopathogens. Teosinte is the grass plant recognized as the progenitor of modern maize, domesticated by pre-Hispanic civilizations around 9,000 years ago. Three teosinte species are recognized: Zea diploperennis, Zea perennis, and Zea mays. In this work, the bacterial diversity of three species of Mexican teosinte seeds was explored by massive sequencing of 16S rRNA amplicons. Streptomyces, Acinetobacter, Olivibacter, Erwinia, Bacillus, Pseudomonas, Cellvibrio, Achromobacter, Devosia, Lysobacter, Sphingopyxis, Stenotrophomonas, Ochrobactrum, Delftia, Lactobacillus, among others, were the bacterial genera mainly represented. The bacterial alpha diversity in the seeds of Z. diploperennis was the highest, while the alpha diversity in Z. mays subsp. mexicana race was the lowest observed among the species and races. The Mexican teosintes analyzed had a core bacteriome of 38 bacterial genera, including several recognized plant growth promoters or fungal biocontrol agents such as Agrobacterium, Burkholderia, Erwinia, Lactobacillus, Ochrobactrum, Paenibacillus, Pseudomonas, Sphingomonas, Streptomyces, among other. Metabolic inference analysis by PICRUSt2 of bacterial genera showed several pathways related to plant growth promotion (PGP), biological control, and environmental adaptation. The implications of these findings are far-reaching, as they highlight the existence of an exceptional bacterial germplasm reservoir teeming with potential plant growth promotion bacteria (PGPB). This reserve holds the key to cultivating innovative bioinoculants and formidable fungal antagonistic strains, thereby paving the way for a more sustainable and eco-friendly approach to agriculture. Embracing these novel NGS-based techniques and understanding the profound impact of the vertical transference of microorganisms from seeds could revolutionize the future of agriculture and develop a new era of symbiotic harmony between plants and microbes.

Creation of doubled haploid lines of maize <i>Zea mays</i> L. by resynthesis from a tetraploid population

The search for new, effective methods for broadening the genetic polymorphism of the original breeding material remains one of important problems of hybrid maize breeding. Globally, breeding of commercial maize varieties and hybrids is carried out using diploid genotypes, whereas tetraploid sources of initial material and wild relatives of maize are poorly involved in the breeding process. The direct heteroploid crosses between diploid and tetraploid genotypes lead to the formation of weakly fertile or completely sterile triploid hybrids, which are cytologically unstable in subsequent generations. Tetraploid maize (2n=40), as well as some wild relatives with tetraploid genome, such as Zea perennis Hitchk. (2n=40) and Tripsacum dactiloides (L.) L. (2n=72), are attractive to breeders as sources for improving economically valuable traits. The attractiveness of resynthesized diploid lines is explained by the fact that unequal crossing over between homologous chromosomes forming polyvalent associations of chromosomes, more chromosomal rearrangements occur in tetraploids than in diploid genotypes, the chromosomes of which form bivalents. Synthetic tetraploid populations of maize and its tetraploid wild relatives have great potential of variability for improving diploid maize. The authors proposed a direct method for the resynthesis of doubled haploid lines using haploid induction and an indirect method for obtaining diploid lines by heteroploid crossing and subsequent segregation of a triploid hybrid in the progeny. The method of resynthesizing the tetraploid maize genome to diploid serves as an ideal model for studying the processes of crossing over in meiosis between multivalent associations of homologous chromosomes; it is promising for obtaining diploid lines with an increased frequency of recombination between the homologous chromosomes of different genomes, combined into a common one, and can serve as a source for obtaining aneuploid series.

Multispecies polyploidization, chromosome shuffling, and genome extraction in Zea/Tripsacum hybrids.

By hybridization and special sexual reproduction, we sequentially aggregated Zea mays, Zea perennis, and Tripsacum dactyloides in an allohexaploid, backcrossed it with maize, derived self-fertile allotetraploids of maize and Z. perennis by natural genome extraction, extended their first six selfed generations, and finally constructed amphitetraploid maize using nascent allotetraploids as a genetic bridge. Transgenerational chromosome inheritance, subgenome stability, chromosome pairings and rearrangements, and their impacts on an organism's fitness were investigated by fertility phenotyping and molecular cytogenetic techniques genomic in situ hybridization (GISH) and fluorescence in situ hybridization (FISH). Results showed that diversified sexual reproductive methods produced highly differentiated progenies (2n = 35-84) with varying proportions of subgenomic chromosomes, of which one individual (2n = 54, MMMPT) overcame self-incompatibility barriers and produced a self-fertile nascent near-allotetraploid by preferentially eliminating Tripsacum chromosomes. Nascent near-allotetraploid progenies showed persistent chromosome changes, intergenomic translocations, and rDNA variations for at least up to the first six selfed generations; however, the mean chromosome number preferably maintained at the near-tetraploid level (2n = 40) with full integrity of 45S rDNA pairs, and a trend of decreasing variations by advancing generations with an average of 25.53, 14.14, and 0.37 for maize, Z. perennis, and T. dactyloides chromosomes, respectively. The mechanisms for three genome stabilities and karyotype evolution for formatting new polyploid species were discussed.

Integrated single-molecule real-time sequencing and RNA sequencing reveal the molecular mechanisms of salt tolerance in a novel synthesized polyploid genetic bridge between maize and its wild relatives

BackgroundTripsacum dactyloides (2n = 4x = 72) and Zea perennis (2n = 4x = 40) are tertiary gene pools of Zea mays L. and exhibit many abiotic adaptations absent in modern maize, especially salt tolerance. A previously reported allopolyploid (hereafter referred to as MTP, 2n = 74) synthesized using Zea mays, Tripsacum dactyloides, and Zea perennis has even stronger salt tolerance than Z. perennis and T. dactyloides. This allopolyploid will be a powerful genetic bridge for the genetic improvement of maize. However, the molecular mechanisms underlying its salt tolerance, as well as the key genes involved in regulating its salt tolerance, remain unclear.ResultsSingle-molecule real-time sequencing and RNA sequencing were used to identify the genes involved in salt tolerance and reveal the underlying molecular mechanisms. Based on the SMRT-seq results, we obtained 227,375 reference unigenes with an average length of 2300 bp; most of the unigenes were annotated to Z. mays sequences (76.5%) in the NR database. Moreover, a total of 484 and 1053 differentially expressed genes (DEGs) were identified in the leaves and roots, respectively. Functional enrichment analysis of DEGs revealed that multiple pathways responded to salt stress, including “Flavonoid biosynthesis,” “Oxidoreductase activity,” and “Plant hormone signal transduction” in the leaves and roots, and “Iron ion binding,” “Acetyl-CoA carboxylase activity,” and “Serine-type carboxypeptidase activity” in the roots. Transcription factors, such as those in the WRKY, B3-ARF, and bHLH families, and cytokinin negatively regulators negatively regulated the salt stress response. According to the results of the short time series-expression miner analysis, proteins involved in “Spliceosome” and “MAPK signal pathway” dynamically responded to salt stress as salinity changed. Protein–protein interaction analysis revealed that heat shock proteins play a role in the large interaction network regulating salt tolerance.ConclusionsOur results reveal the molecular mechanism underlying the regulation of MTP in the response to salt stress and abundant salt-tolerance-related unigenes. These findings will aid the retrieval of lost alleles in modern maize and provide a new approach for using T. dactyloides and Z. perennis to improve maize.

A comparison of the direct and indirect defence abilities of cultivated maize versus perennial and annual teosintes

The transition from a perennial to an annual life cycle, as well as domestication, are expected to increase plant growth and reproduction at the same time that anti-herbivore defences are reduced. Here, we investigated the effects of the life-history transition (the perennial teosinte Zea diploperennis to the annual teosinte Z. mays ssp. mexicana) and domestication of Zea (annual teosinte to the modern maize Z. mays ssp. mays) on direct and indirect defences against the fall armyworm Spodoptera frugiperda. The direct defence of Zea was assessed by larval survival and nutritional indices based on food intake and utilisation. Indirect defence was measured in terms of the olfactory preference of the night-active predatory earwig Doru luteipes for nocturnal herbivore-induced plant volatiles (HIPVs) from the teosintes and maize. Larval growth and survival were reduced on teosintes relative to maize. Whilst larvae fed on perennial teosinte had lower food intake indices, those on annual teosinte showed lower food utilisation indices relative to maize. The earwig preferred HIPVs emitted by teosintes over those by maize, but it did not discriminate between odours of herbivore-damaged annual and perennial teosinte. The nocturnal HIPV blend from maize contained the lowest total amount of fatty acid derivatives, while it had higher total amounts of terpenes compared to teosintes. Our study shows that the teosintes are better defended than maize in terms of direct and indirect defences; however, the perennial teosinte have stronger direct defences against the fall armyworm than the annual teosinte.

Allopolyploidization facilitates gene flow and speciation among corn, Zea perennis and Tripsacum dactyloides

Main conclusionTripsacum dactyloides is closely related to Zea mays since Zea perennis and the MTP tri- species hybrid have four possible reproductive modes.Eastern gamagrass (Tripsacum dactyloides L.) and tetraploid perennial teosinte (Zea perennis) are well known to possess genes conferring resistance against biotic and abiotic stresses as well as adaptation to flood and aluminum toxic soils. However, plant breeders have been hampered to utilize these and other beneficial traits for maize improvement due to sterility in their hybrids. By crossing a tetraploid maize-inbred line × T. dactyloides, a female fertile hybrid was produced that was crossed with Z. perennis to yield a tri-genomic female fertile hybrid, which was backcrossed with diploid maize to produce BC1 and BC2. The tri-genomic hybrid provided a new way to transfer genetic material from both species into maize by utilizing conventional plant breeding methods. On the basis of cytogenetic observations using multi-color genomic in situ hybridization, the progenies were classified into four groups, in which chromosomes could be scaled both up and down with ease to produce material for varying breeding and genetic purposes via apomixis or sexual reproduction. In the present study, pathways were found to recover maize and to obtain specific translocations as well as a speedy recovery of the T. dactyloides–maize addition line in a second backcross generation. However, phenotypes of the recovered maize were in most cases far from maize as a result of genetic load from T. dactyloides and Z. perennis, and could not be directly used as a maize-inbred line but could serve as an intermediate material for maize improvement. A series of hybrids was produced (having varying chromosome number, constitution, and translocations) with agronomic traits from all three parental species. The present study provides an application of overcoming the initial interspecific barriers among these species. Moreover, T. dactyloides is closely related to Z. mays L. ssp. mays since Z. perennis and the MTP tri- species hybrid have four possible reproductive modes.

Morphological and Climatic Variability of Teosinte (Zea spp.) and Relationships Among Taxa

Abstract—The wild species of the genus Zea comprise nine different taxa, including annual and perennial, diploid and tetraploid species, distributed from northern Mexico to Costa Rica. Due to the great variability existing among species, the aim of this work was to evaluate the morphological and climatic variability patterns and phylogenetic relationships among species, based on morphological characters. Two hundred and seventy-six populations of known species and races were included; 15 individuals per population were planted. From each individual, 19 morphological and physiological traits were measured, and at each collection site 23 climatic descriptors were obtained. Both data sets were analyzed with multivariate analysis. For the phylogenetic analysis 17 morphological variables were transformed to character states using GAP-WEIGHTING. With multivariate analyses, it was possible to determine the existence of well-defined groups. Species, and races of different subspecies, were found to be clearly delimited by geographic regions, climatic characteristics, altitudes, and distinct morphological features. The phylogenetic relationships found are congruent with those identified in similar studies based on molecular data. Morphological data on their own cannot give enough information to infer divergence times. In this context, multivariate and phylogenetic analyses with morphological data are taxonomically of great importance for identifying species and subspecies of genus Zea. At species level, the study has added elements to distinguish between Zea diploperennis from the states of Nayarit and Jalisco, between Zea perennis from Michoacán and Jalisco, and between Zea luxurians from Oaxaca and Guatemala.

Temperaturas cardinales de desarrollo del teocintle (Zea spp.)

El teocintle representa una fuente importante de genes para el mejoramiento del maíz (Zea mays L.); sin embargo, poco se ha avanzado en la caracterización de sus respuestas a diversas condiciones ambientales, incluyendo el desarrollo del teocintle en función de la temperatura, siendo ésta una variable clave para su adaptación y distribución. La temperatura base (Tb), temperatura óptima (To) y temperatura umbral máxima (Tu) son conocidas también como temperaturas cardinales del desarrollo y son particulares para cada especie, genotipo y etapa fenológica. El objetivo del presente estudio fue determinar las temperaturas cardinales de poblaciones de los teocintles Zea perennis, Zea diploperennis, Zea mays subsp. mexicana razas Chalco, Durango, Mesa Central y Nobogame y Zea mays subsp. parviglumis o raza Balsas. Se utilizaron datos de experimentos de campo realizados entre 1986 y 2005 donde se monitorearon datos de días a antesis (F), datos de temperatura y precipitación. Se utilizaron modelos lineales y curvilíneos para explicar la variación de la tasa de desarrollo de la etapa siembra-antesis (1/F) en función de la variación de la temperatura media (Tm) del período siembra-floración. Los resultados mostraron que la relación entre Tm y 1/F es descrita por una función curvilínea, ajustándose en todos los casos un modelo cuadrático-exponencial, con un valor de r2> 0.73. El valor de Tb varió de 8.02 a 14.31 °C, el de To entre 23.5 y 31.67 °C y el de Tu entre 29.43 y 40.61 °C. Se concluye que los valores de temperaturas cardinales del teocintle varían entre y dentro de razas, lo que indica adaptación a diversas condiciones térmicas para las razas de teocintle estudiadas.

Ecogeography of teosinte.

Adaptation of crops to climate change has motivated an increasing interest in the potential value of novel traits from wild species; maize wild relatives, the teosintes, harbor traits that may be useful to maize breeding. To study the ecogeographic distribution of teosinte we constructed a robust database of 2363 teosinte occurrences from published sources for the period 1842–2016. A geographical information system integrating 216 environmental variables was created for Mexico and Central America and was used to characterize the environment of each teosinte occurrence site. The natural geographic distribution of teosinte extends from the Western Sierra Madre of the State of Chihuahua, Mexico to the Pacific coast of Nicaragua and Costa Rica, including practically the entire western part of Mesoamerica. The Mexican annuals Zea mays ssp. parviglumis and Zea mays ssp. mexicana show a wide distribution in Mexico, while Zea diploperennis, Zea luxurians, Zea perennis, Zea mays ssp. huehuetenangensis, Zea vespertilio and Zea nicaraguensis had more restricted and distinct ranges, representing less than 20% of the total occurrences. Only 11.2% of teosinte populations are found in Protected Natural Areas in Mexico and Central America. Ecogeographical analysis showed that teosinte can cope with extreme levels of precipitation and temperatures during growing season. Modelling teosinte geographic distribution demonstrated congruence between actual and potential distributions; however, some areas with no occurrences appear to be within the range of adaptation of teosintes. Field surveys should be prioritized to such regions to accelerate the discovery of unknown populations. Potential areas for teosintes Zea mays ssp. mexicana races Chalco, Nobogame, and Durango, Zea mays ssp. huehuetenangensis, Zea luxurians, Zea diploperennis and Zea nicaraguensis are geographically separated; however, partial overlapping occurs between Zea mays ssp. parviglumis and Zea perennis, between Zea mays ssp. parviglumis and Zea diploperennis, and between Zea mays ssp. mexicana race Chalco and Zea mays ssp. mexicana race Central Plateau. Assessing priority of collecting for conservation showed that permanent monitoring programs and in-situ conservation projects with participation of local farmer communities are critically needed; Zea mays ssp. mexicana (races Durango and Nobogame), Zea luxurians, Zea diploperennis, Zea perennis and Zea vespertilio should be considered as the highest priority taxa.

Cytological diploidization of paleopolyploid genus Zea: Divergence between homoeologous chromosomes or activity of pairing regulator genes?

Cytological diploidization process is different in autopolyploid and allopolyploid species. Colchicine applied at the onset of meiosis suppresses the effect of pairing regulator genes resulting multivalents formation in bivalent-forming species. Colchicine treated maizes (4x = 2n = 20, AmAmBmBm) showed up to 5IV, suggesting pairing between chromosomes from genomes homoeologous Am and Bm. In untreated individuals of the alloautooctoploid Zea perennis (8x = 2n = 40, ApApAp´Ap´Bp1Bp1Bp2Bp2) the most frequent configuration was 5IV+10II (formed by A and B genomes, respectively). The colchicine treated Z. perennis show up to 10IV revealing higher affinity within genomes A and B, but any homology among them. These results suggest the presence of a paring regulator locus (PrZ) in maize and Z. perennis, whose expression is suppressed by colchicine. It could be postulated that in Z. perennis, PrZ would affect independently the genomes A and B, being relevant the threshold of homology, the fidelity of pairing in each genomes and the ploidy level. Cytological analysis of the treated hexaploid hybrids (6x = 2n = 30), with Z. perennis as a parental, strongly suggests that PrZ is less effective in only one doses. This conclusion was reinforced by the homoeologous pairing observed in untreated dihaploid maizes, which showed up to 5II. Meiotic behaviour of individuals treated with different doses of colchicine allowed to postulate that PrZ affect the homoeologous association by controlling entire genomes (Am or Bm) rather than individual chromosomes. Based on cytological and statistical results it is possible to propose that the cytological diploidization in Zea species occurs by restriction of pairing between homoeologous chromosomes or by genetical divergence of the homoeologous chromosomes, as was observed in untreated Z. mays ssp. parviglumis. These are independent but complementary systems and could be acting jointly in the same nucleus.

Do assortative mating and immigrant inviability help maintain population genetic structuring of an herbivore on a crop and a wild relative?

Population genetic structuring is common among herbivorous insects and frequently is associated with divergent host plants, such as crops and their wild relatives. Previous studies showed population genetic structuring in corn leafhopper Dalbulus maidis in Mexico, such that the species consists of two sympatric, host plant-associated populations: an abundant and widespread "pestiferous" population on maize (Zea mays mays), and a small and localized "wild" population on perennial teosinte (Zea diploperennis), a maize wild relative with a limited distribution. This study addressed whether assortative mating and immigrant inviability mediate genetic structuring of corn leafhopper by comparing the mating and reproductive successes of pestiferous and wild females that colonize their nonassociated host plants against the successes of females colonizing their associated host plants. Assortative mating was assessed by comparing mating frequencies and premating and mating times among females of each population on each host plant; immigrant inviability was assessed by comparing, across two generations, the fecundity, survival, development time, sex ratio, and population growth rate among leafhopper populations and host plants. Our results showed that on maize, and compared to resident, pestiferous females, wild females were more likely to mate, and greater proportions of their offspring survived to adult stage and were daughters; consequently, the per-generation population growth rate on maize was greater for immigrant, wild leafhoppers compared to resident, pestiferous leafhoppers. Our results suggested that wild leafhoppers emigrating to maize have a fitness advantage over resident, pestiferous leafhoppers, while immigrant pestiferous and resident wild leafhoppers on teosinte have similar fitnesses.

Egg Parasitoids ofDalbulus maidison Wild Teosintes in Mexico

Little is known about parasitoids that attack insect pests on wild host plants, including wild teosintes. Sentinel teosinte plants with eggs of the specialist herbivore pest, the corn leafhopper, Dalbulus maidis (DeLong) (Hemiptera: Cicadellidae), were used to attract and capture egg parasitoid species in natural habitats of annual teosinte Zea mays ssp. parviglumis Iltis & Doebley, which is the direct ancestor of maize (Zea mays ssp. mays L.), and perennial teosinte Zea perennis (Hitchc.) Reeves & Mangelsdorf in central Mexico. In annual teosinte, eggs of D. maidis were parasitized by Anagrus incarnatus Haliday and Anagrus columbi Perkins (Hymenoptera: Mymaridae), as well as Paracentrobia sp. near subflava (Girault) and Pseudoligosita sp. near longifrangiata (Viggiani) (Hymenoptera: Trichogrammatidae); in perennial teosinte, they were parasitized by A. incarnatus and Pseudoligosita sp. near longifrangiata. All the egg parasitoids, recorded for the first time from wild teosintes, have been previously known from the same leafhopper pest on cultivated maize. Thus, their conservation in wild teosinte habitats may be important for enhancing natural biological control of the corn leafhopper in adjacent maize fields.

A Bird in the Hand Versus Two in the Bush? The Specialist Leafhopper Dalbulus maidis (Hemiptera: Cicadellidae) Does Not Discriminate Against Sub-optimal Host Plants (Zea spp.).

The corn leafhopper [Dalbulus maidis (DeLong & Wolcott)] is a specialist on Zea (Poaceae) that coevolved with maize (Zea mays mays) and its teosinte (Zea spp.) relatives. This study tested the hypothesis that host acceptance by females varies among Zea hosts, and is correlated with variation in defensive levels across those hosts. Prior studies revealed differences in plant defenses among Zea hosts and corresponding differences in corn leafhopper performance. Thus, host acceptance was expected to be correlated with defensive levels and offspring performance across Zea hosts, following the hypothesis that offspring performance mediates host preference. In parallel, host acceptance was expected to be correlated with transitions in life history strategy (perennial to annual life cycle), domestication status (wild to domesticated), and breeding intensity (landrace to hybrid variety) in Zea because variation in defensive levels and corn leafhopper performance were shown in prior studies to be correlated with those transitions. The study's hypotheses were tested by comparing, under no-choice conditions, host acceptance by corn leafhopper of a suite of Zea hosts encompassing those transitions: perennial teosinte (Zea diploperennis), Balsas teosinte (Zea mays parviglumis), and landrace and commercial hybrid maize. The results did not show differences in host acceptance for oviposition or feeding among the hosts. Thus, under no-choice conditions, all Zea hosts may be similarly acceptable for feeding and oviposition, despite marked ovipositional preferences under choice conditions and poorer offspring performance on teosintes relative to maize shown previously. The results suggested also that oviposition frequency per plant by females was not correlated with their offspring's performance.

Plastid phylogenomic study of species within the genus Zea: rates and patterns of three classes of microstructural changes.

This project examines the relationships within the genus Zea using complete plastid genomes (plastomes). While Zea mays has been well studied, congeneric species have yet to be as thoroughly examined. For this study four complete plastomes and a fifth nearly complete plastome were sequenced in the five species (Zea diploperennis, Zea perennis, Zea luxurians, Zea nicaraguensis, and Zea mays subsp. huehuetenangensis) by Sanger or next-generation methods. An analysis of the microstructural changes, such as inversions, insertion or deletion mutations (indels) and determination of their frequencies were performed for the complete plastomes. It was determined that 193 indels and 15 inversions occurred across the examined plastomes of Zea. Tandem repeat indels were the most common type of microstructural change observed. Divergence times were estimated using a noncorrelated relaxed clock method. Divergence dates for specific nodes relative to Zea were calculated to fall between 38,000years before present (YBP) for the subspecies included in this study and 23,000 YBP for section Luxuriantes included in this study. The stem lineage of all Zea species was calculated to have diverged at 176,000 YBP. The calculated mutation rates for the genus fell within the range of 1.7E-8 to 3.5E-8 microstructural changes per site per year. These rates of change are not uniform, despite the close relationships of taxa in this study. Phylogenomic analyses using full plastome alignments were also conducted to compare tree topologies from different types of mutations. In most cases, the previous work examining Zea mitochondrial and nuclear data was confirmed.

Early Development of Leaf Trichomes Is Associated With Decreased Damage in Teosinte, Compared With Maize, bySpodoptera frugiperda(Lepidoptera: Noctuidae)

Invertebrate herbivores prefer younger over older plant stages. Therefore, defensive traits against herbivores during early plant ontogeny are important. Defensive chemical and physical traits are well-studied in domesticated plants, but not in their wild relatives. Little is known about the function of trichomes, a physical defense against herbivore arthropods that damage cultivated plants and their wild ancestors. Maize is one of the most important crops in the world, but few studies have been conducted on the physical defenses during early ontogeny of maize and its wild relative teosinte. Therefore, the objective of this study was to characterize the density of trichomes (macrohairs) in maize and teosintes, and to evaluate the chewing damage by Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae) larvae on the 6-leaf stage of 1) perennial teosinte Zea perennis (Poaceae), 2) annual teosinte Zea mays ssp. parviglumis , 3) landrace maize, and 4) on the 2-leaf stage of the landrace maize. Significantly less damage occurred in both teosinte species, which showed pubescence (trichomes) on the upper leaf-blade, but not on the midrib leaf surface. The highest trichome density was found on Z. perennis , followed by Z. mays ssp. parviglumis at the 6-leaf stage. No trichomes were found on the landrace maize, at the 6-leaf stage or 2-leaf stage. Results suggest that trichomes play an important role in preventing damage by chewing larvae on the ancestors of maize. Genes that promote macrohair initiation in teosintes during early vegetative development could be incorporated into maize plants in the future.

Effect of Herbivore Insect Pest Age on Fecundity and Attractiveness to Egg Parasitoids in Maize and Its Wild Relative, Teosinte

Little is known about insect pest ontogeny, with respect to fecundity, on domesticated plants and their wild relatives, and the effect of fecundity on parasitoids. The aim was to determine fecundity in young (2 wk old) and mature (8 wk old) females of the pest Dalbulus maidis (DeLong) (Hemiptera: Cicadellidae) on maize, Zea mays ssp. mays , and its wild relative, teosinte. The effect of fecundity on parasitoid attraction was also evaluated. First, the fecundity of young D. maidis females and their attractiveness to parasitoids was evaluated in the native maize race “maiz ancho” and in the teosinte Zea perennis . Next, the fecundity of mature females and their attractiveness to parasitoids was evaluated in the native maize race “maiz ancho” at two juvenile stages, and in the teosintes Zea mays ssp. parviglumis and Z. perennis . Whereas young females laid more eggs on maize than on Z. perennis , mature females laid similar numbers of eggs on all plants studied. Anagrus incarnatus Haliday (Hymenoptera: Mymaridae) was the most abundant egg parasitoid. Eggs from young versus mature D. maidis females attracted more parasitoids. Furthermore, more parasitoid adults emerged from eggs produced by young D. maidis females on maize than on Z. perennis , whereas no difference was seen in the number of parasitoid adults emerging from eggs produced by mature D. maidis females from any of the four plant treatments. These results indicate that fecundity changes with herbivore pest age and egg parasitoid attraction depends on herbivore density; in this case, attraction was higher for young D. maidis females.

Genomic affinities revealed by GISH suggests intergenomic restructuring between parental genomes of the paleopolyploid genus Zea.

The present work compares the molecular affinities, revealed by GISH, with the analysis of meiotic pairing in intra- and interspecific hybrids between species of Zea obtained in previous works. The joint analysis of these data provided evidence about the evolutionary relationships among the species from the paleopolyploid genus Zea (maize and teosintes). GISH and meiotic pairing of intraspecific hybrids revealed high genomic affinity between maize (Zea mays subsp. mays) and both Zea mays subsp. parviglumis and Zea mays subsp. mexicana. On the other hand, when Zea mays subsp. huehuetenanguensis DNA was probed on maize chromosomes, a lower affinity was detected, and the pattern of hybridization suggested intergenomical restructuring between the parental genomes of maize. When DNA from Zea luxurians was used as probe, homogeneous hybridization signals were observed through all maize chromosomes. Lower genomic affinity was observed when DNA from Zea diploperennis was probed on maize chromosomes, especially at knob regions. Maize chromosomes hybridized with Zea perennis DNA showed hybridization signals on four chromosome pairs: two chromosome pairs presented hybridization signal in only one chromosomal arm, whereas four chromosome pairs did not show any hybridization. These results are in agreement with previous GISH studies, which have identified the genomic source of the chromosomes involved in the meiotic configurations of Z. perennis × maize hybrids. These findings allow postulating that maize has a parental genome not shared with Z. perennis, and the existence of intergenomic restructuring between the parental genomes of maize. Moreover, the absence of hybridization signals in all maize knobs indicate that these heterochromatic regions were lost during the Z. perennis genome evolution.

The effect of different genome and cytoplasm on meiotic pairing in maize newly synthetic polyploids

Abstract Allopolyploidization plays the special role in the evolution of many crops. Moreover, the evolution in early stage of some allopolyploidization events is predicted to be effected by nuclear-cytoplasmic interactions. Maize and teosintes are well model system for study of genetic recombination in allopolyploidization. In order to investigate the effects of genome organization and cytoplasm on genome evolution in newly synthesized allopolyploids (neoallopolyploids), a series of neoallopolyploids were produced by reciprocal crosses of maize and Zea perennis. By using dual-color genomic in situ hybridization, intra- and intergenomic meiosis pairing of these polyploids were quantified and compared with regard to its genome organization and cytoplasm background. In the four neoallopolyploids, the stability of maize genome is consistently lower than that of Z. perennis genome. Additional, the stability of maize genome is affected by genome ploidy. The cytoplasm, genome composition and their interaction do have the special role in chromosome paring and the meiosis behaviors in Zea allopolyploids vary significantly and showed non-diploidization. Z. perennis cytoplasm may give a relatively relaxed environment for maize genome.

Perennial aneuploidy as a potential material for gene introgression between maize and Zea perennis

Hybridization, which allows for gene flow between crops, is difficult between maize and Zea perennis. In this study, we aim to initiate and study gene flow between maize and Z. perennis via a special aneuploid plant (MDT) derived from an interspecific hybrid of the two species. The chromosome constitution and morphological characters of MDT as well as certain backcross progenies were examined. Results from genomic in situ hybridization (GISH) indicate that aneuploid MDT consisted of nine maize chromosomes and 30 Z. perennis chromosomes. The backcross progenies of MDT×maize displayed significant diversity of vegetative and ear morphology; several unusual plants with specific chromosome constitution were founded in its progenies. Some special perennial progeny with several maize chromosomes were obtained by backcrossing MDT with Z. perennis, and the first whole chromosome introgression from maize to Z. perennis was detected in this study. With this novel material and method, a number of maize-tetraploid teosinte addition or substitution lines can be generated for further study, which has great significance to maize and Z. perennis genetic research, especially for promoting introgression and transferring desirable traits.