Project description:Archaeological cobs from Paredones and Huaca Prieta (Peru) represent some of the oldest maize known to date, yet they present relevant phenotypic traits corresponding to domesticated maize. This contrasts with the earliest Mexican macro-specimens from Guila Naquitz and San Marcos, which are phenotypically intermediate for these traits, even though they date more recently in time. To gain insights into the origins of ancient Peruvian maize, we sequenced DNA from three Paredones specimens dating ~6700-5000 calibrated years before present (BP), conducting comparative analyses with two teosinte subspecies (Zea mays ssp. mexicana and parviglumis) and extant maize, that include highland and lowland landraces from Mesoamerica and South America. We show that Paredones maize originated from the same domestication event as Mexican maize and was domesticated by ~6700 BP, implying rapid dispersal followed by improvement. Paredones maize shows no relevant gene flow from mexicana, smaller than that observed in teosinte parviglumis. Thus, Paredones samples represent the only maize without confounding mexicana variation found to date. It also harbors significantly fewer alleles previously found to be adaptive to highlands, but not of alleles adaptive to lowlands, supporting a lowland migration route. Our overall results imply that Paredones maize originated in Mesoamerica, arrived in Peru without mexicana introgression through a rapid lowland migration route, and underwent improvements in both Mesoamerica and South America.
Project description:Through domestication, humans have substantially altered the morphology of Zea mays ssp. parviglumis (teosinte) into the currently recognizable maize. A wealth of archeological and population genetic data has established maize as a model system for studying domestication , genome evolution and the genetics and evolution of complex traits. We used expression profiling of 18,242 genes for 38 diverse maize genotypes and 18 teosinte genotypes to examine how domestication has re-shaped the transcriptome of maize seedlings. We detected evidence for more than 600 genes having significantly different expression levels in maize compared to teosinte as well as 800 genes with significantly altered co-expression profiles reflective of substantial rewiring of the transcriptome since domestication. These genes likely include loci with altered expression due to domestication. The genes with altered expression show a significant enrichment for genes located in regions that previous population genetic analyses have identified as having undergone a selective sweep during maize domestication; thirty-two genes previously identified as putative targets of selection also exhibit altered expression levels and co-expression relationships. We also identified 45 genes with altered, primarily higher, expression in inbred relative to out-crossed teosinte. These genes are over-represented for genes that function in response to biotic stress and may reflect responses to the effects of inbreeding. This study not only documents alterations in the maize transcriptome following domestication and identifies several genes that may have contributed to the evolution of maize but also highlights the complementary information that can be gained by combining gene expression with population genetic analyses.
Project description:Modification of cis regulatory elements to produce differences in gene expression level, localization, and timing is an important mechanism by which organisms evolve divergent adaptations. To examine gene regulatory change during the domestication of maize from its wild progenitor, teosinte, we assessed allele-specific expression in a collection of maize and teosinte inbreds and their F1 hybrids using three tissues from different developmental stages. Our use of F1 hybrids represents the first study in a domesticated crop and wild progenitor that dissects cis and trans regulatory effects to examine characteristics of genes under various cis and trans regulatory regimes. We find evidence for consistent cis regulatory divergence that differentiates maize from teosinte in approximately 4% of genes. These genes are significantly correlated with genes under selection during domestication and crop improvement, suggesting an important role for cis regulatory elements in maize evolution.
Project description:MicroRNAs (miRNAs) are small non-coding RNAs that play essential roles in plant growth and development. We conducted a genome-wide survey of maize miRNA genes, characterizing their structure, expression, and evolution. Computational approaches based on homology and secondary structure modeling identified 150 high-confidence genes within 26 miRNA families. For 25 families, expression was verified by deep-sequencing of small RNA libraries that were prepared from an assortment of maize tissues. PCR-RACE amplification of 68 miRNA transcript precursors, representing 18 families conserved across several plant species, showed that splice variation and the use of alternative transcriptional start and stop sites is common within this class of genes. Comparison of sequence variation data from diverse maize inbred lines versus teosinte accessions suggest that the mature miRNAs are under strong purifying selection while the flanking sequences evolve equivalently to other genes. Since maize is derived from an ancient tetraploid, the effect of whole-genome duplication on miRNA evolution was examined. We found that, like protein-coding genes, duplicated miRNA genes underwent extensive gene-loss, with ~35% of duplicate homeologous miRNA genes retained. This number is higher than that observed with protein-coding genes. A search for putative miRNA targets indicated a bias towards genes in regulatory and metabolic pathways. As maize is one of the principal models for plant growth and development, this study will serve as a foundation for future research into the functional roles of miRNA genes. Surveying miRNA genes in 5 maize tissues (root, seedling, tassel, ear, and pollen) by sequencing small RNA libraries using the Illumina Genome Analyzer
Project description:DNA methylation is a ubiquitous chromatin feature — in maize, more than 25% of cytosines in the genome are methylated. Recently, major progress has been made in describing the molecular mechanisms driving methylation, yet variation and evolution of the methylation landscape during maize domestication remain largely unknown. Here we leveraged whole-genome sequencing (WGS) and whole-genome bisulfite sequencing (WGBS) on populations of modern maize, landrace, and teosinte (Zea mays ssp. parviglumis) to investigate the adaptive and phenotypic consequences of methylation variations in maize. By using a novel estimation approach, we inferred the methylome site frequency spectrum (mSFS) to estimate forward and backward methylation mutation rates and selection coefficients. We only found weak evidence for direct selection on DNA methylation in any context, but thousands of differentially methylated regions (DMRs) were identified in population-wide that are correlated with recent selection. Further investigation revealed that DMRs are enriched in 5’ untranslated regions, and that maize hypomethylated DMRs likely helped rewire distal gene regulation. For two trait-associated DMRs, vgt1-DMR and tb1DMR, our HiChIP data indicated that the interactive loops between DMRs and respective downstream genes were present in B73, a modern maize line, but absent in teosinte. Functional analyses suggested that these DMRs likely served as cis-acting elements that modulated gene regulation after domestication. Our results enable a better understanding of the evolutionary forces acting on patterns of DNA methylation and suggest a role of methylation variation in adaptive evolution.
Project description:Meiotic drivers subvert Mendelian expectations by manipulating reproductive development to bias their own transmission. Chromosomal drive typically functions in asymmetric female meiosis, while gene drive is normally postmeiotic and typically found in males. Cryptic drive is thought to be pervasive and can be unleashed following hybridization with a naïve genome, resulting in sterility and hybrid incompatibility. Using single molecule and single pollen genome sequencing, we describe an instance of gene drive in hybrids between maize (Zea mays ssp. mays) and teosinte mexicana (Zea mays ssp. mexicana), that depends on RNA interference (RNAi) in the male germline. Multiple hairpin-derived small RNA from mexicana target a novel domestication gene, Teosinte Drive Responder, that is required for pollen fertility and has undergone selection for immunity to RNAi. Introgression of mexicana into early cultivated maize is thought to have been critical to its geographical dispersal throughout the Americas. A survey of maize landraces and sympatric populations of teosinte mexicana reveals allelic bias at genes required for RNAi on at least 4 chromosomes that are also subject to gene drive in pollen from synthetic hybrids. Teosinte Pollen Drive likely played a major role in maize domestication, and offers an explanation for the widespread abundance of hairpin-encoded and other endogenous small RNA in the germlines of plants and animals.
Project description:Meiotic drivers subvert Mendelian expectations by manipulating reproductive development to bias their own transmission. Chromosomal drive typically functions in asymmetric female meiosis, while gene drive is normally postmeiotic and typically found in males. Cryptic drive is thought to be pervasive and can be unleashed following hybridization with a naïve genome, resulting in sterility and hybrid incompatibility. Using single molecule and single pollen genome sequencing, we describe an instance of gene drive in hybrids between maize (Zea mays ssp. mays) and teosinte mexicana (Zea mays ssp. mexicana), that depends on RNA interference (RNAi) in the male germline. Multiple hairpin-derived small RNA from mexicana target a novel domestication gene, Teosinte Drive Responder, that is required for pollen fertility and has undergone selection for immunity to RNAi. Introgression of mexicana into early cultivated maize is thought to have been critical to its geographical dispersal throughout the Americas. A survey of maize landraces and sympatric populations of teosinte mexicana reveals allelic bias at genes required for RNAi on at least 4 chromosomes that are also subject to gene drive in pollen from synthetic hybrids. Teosinte Pollen Drive likely played a major role in maize domestication, and offers an explanation for the widespread abundance of hairpin-encoded and other endogenous small RNA in the germlines of plants and animals.
Project description:MicroRNAs (miRNAs) are small non-coding RNAs that play essential roles in plant growth and development. We conducted a genome-wide survey of maize miRNA genes, characterizing their structure, expression, and evolution. Computational approaches based on homology and secondary structure modeling identified 150 high-confidence genes within 26 miRNA families. For 25 families, expression was verified by deep-sequencing of small RNA libraries that were prepared from an assortment of maize tissues. PCR-RACE amplification of 68 miRNA transcript precursors, representing 18 families conserved across several plant species, showed that splice variation and the use of alternative transcriptional start and stop sites is common within this class of genes. Comparison of sequence variation data from diverse maize inbred lines versus teosinte accessions suggest that the mature miRNAs are under strong purifying selection while the flanking sequences evolve equivalently to other genes. Since maize is derived from an ancient tetraploid, the effect of whole-genome duplication on miRNA evolution was examined. We found that, like protein-coding genes, duplicated miRNA genes underwent extensive gene-loss, with ~35% of duplicate homeologous miRNA genes retained. This number is higher than that observed with protein-coding genes. A search for putative miRNA targets indicated a bias towards genes in regulatory and metabolic pathways. As maize is one of the principal models for plant growth and development, this study will serve as a foundation for future research into the functional roles of miRNA genes.
Project description:1 g samples of maize seedling leaf bases were collected from the wild-type (Zheng58) plants and the mutants (bzu3-2). we undertook glycoproteomics analyses of the N-glycans. Based on the libraries of maize protein group and plant N-glycosylation modification in the Uniprot database, we identified 2,194 intact N-glycopeptides, and quantified 181 differentially expressed intact N-glycopeptides (DEGPs)