Project description:Breeding day-neutral strawberry (Fragaria x ananassa Duchesne) is pivotal to extend fruit-bearing season and increase the efficiency of production. However, genetic improvement of day-neutrality by the means of molecular marker technologies remains slow due to genome complexity of octoploid strawberry. This study employs an innovative approach by integrating the Subtracted Diversity Array (SDA) technology and Bulked Segregant Analysis (BSA) to facilitate the identification of molecular markers associated with day-neutrality in octoploid strawberry. A Fragaria Discovery Panel (FDP) containing 287 features specific to strawberry genome was constructed as a platform for rapid screening of DNA polymorphism between one short day (SD) strawberry DNA bulk and three day-neutral (DN) bulks varrying in flowering strength. Differential array hybridisation patterns between the DN and SD bulks revealed a novel molecular marker, FaP2E11, closely linked to CYTOKININ OXIDASE 1 (CKX1) gene possibly involved in promoting flowering under non-inductive condition. Interestingly, a 12 bp deletion was observed within the FaP2E11 sequence cloned from SD genotypes but not DN genotypes. As cytokinin is required to induce flowering, this result indicates that full sequence of FaP2E11 and the sequence with deletion are allelic variants linked to the low enzyme activity CKX1 and the wild type alleles, respectively.
Project description:Common wheat (T. aestivum) converged three subgenomes adapted to different environments. The combinatorial interaction between transcription factors (TFs) and regulatory elements (REs) defines a regulatory circuit that underlies subgenome convergence and divergence. Compared to the relatively conserved gene composition across subgenomes, the intergenic regions with abundant REs is drastically diversified by almost complete TE turnovers, raising major questions regarding how subgenome convergent and divergent regulation is encoded in the highly diversified intergenic regions, and the impact of TE evolution on regulatory conservation and innovation. In the present study, we created genome-wide TF binding catalog to assemble an extensive wheat regulatory network comprising connections among 182 TFs. The different effects of ancient and recent TE insertions on regulatory specificity were observed. Subgenome asymmetric TE expansion is an important source of subgenome divergent TFBS, which help explain the vast occupancy difference across subgenomes. Interestingly, the ancient expansion of RLC_famc1.4-derived TFBS occurred in more than 25% triads promoters. A significant fraction of these TE-derived TFBS subjected to region-specific evolutionary selections, resulting in subgenome-balanced TF binding but unbalanced degeneration of flanking TE sequences. These TE-derived subgenome convergent and divergent regulation linked to subgenome conserved and diversified pathways, suggesting that TEs are an important regulatory driving force contributed to polyploid evolution. Overall, this study demonstrated the impact of TEs on shaping the plasticity and adaptation of common wheat, enriched the theories of TE-promoted transcriptional innovation from the evolutionary aspects of polyploid regulation since first reported by McClintock.
Project description:Polyploidization drives regulatory and phenotypic innovation. How the merger of different genomes contributes to polyploid development is a fundamental issue in evolutionary developmental biology and breeding research. Clarifying this issue is challenging because of genome complexity and the difficulty in tracking stochastic subgenome divergence during development. Recent single-cell sequencing techniques enabled probing subgenome divergent regulation in the context of cellular differentiation. However, analyzing single-cell data suffers from high error rates due to high-dimensionality, noise, and sparsity, and the errors stack up in polyploid analysis due to the increased dimensionality of comparisons between subgenomes of each cell, hindering deeper mechanistic understandings. Here, we developed a quantitative computational framework, pseudo-genome divergence quantification (pgDQ), for quantifying and tracking subgenome divergence directly at the cellular level. Further comparing with cellular differentiation trajectories derived from scRNA-seq data allowed for an examination of the relationship between subgenome divergence and the progression of development. pgDQ produces robust results and is insensitive to data dropout and noise, avoiding high error rates due to multiple comparisons of genes, cells, and subgenomes. A statistical diagonostic approach is proposed to identify genes that are central to subgenome divergence during development, which facilitates the integration of different data modalities, enabling the identification of factors and pathways that mediate subgenome-divergent activity during development. Case studies demonstrated that applying pgDQ to single cell and bulk tissue transcriptome data promotes a systematic and deeper understanding of how dynamic subgenome divergence contributes to developmental trajectories in polyploid evolution.
Project description:The importance and applications of polyploidy have long been recognized, from shaping the evolutionary success of flowering plants to improving agricultural productivity. Recent studies have shown that one of the parental subgenomes in ancient polyploids is generally more dominant - having both retained more genes and being more highly expressed - a phenomenon termed subgenome dominance. How quickly one subgenome dominates within a newly formed polyploid, if immediate or after millions of years, and the genomic features that determine which genome dominates remain poorly understood. To investigate the rate of subgenome dominance emergence, we examined gene expression, gene methylation, and transposable element (TE) methylation in a natural less than 140 year old allopolyploid (Mimulus peregrinus), a resynthesized interspecies triploid hybrid (M. robertsii), a resynthesized allopolyploid (M. peregrinus), and diploid progenitors (M. guttatus and M. luteus). We show that subgenome expression dominance occurs instantly following the hybridization of two divergent genomes and that subgenome expression dominance significantly increases over generations. Additionally, CHH methylation levels are significantly reduced in regions near genes and within transposons in the first generation hybrid, intermediate in the resynthesized allopolyploid, and are repatterned differently between the dominant and submissive subgenomes in the natural allopolyploid. Our analyses reveal that the subgenome differences in levels of TE methylation mirror the increase in expression bias observed over the generations following the hybridization. These findings not only provide important insights into genomic and epigenomic shock that occurs following hybridization and polyploid events, but may also contribute to uncovering the mechanistic basis of heterosis and subgenomic dominance.
Project description:Expression divergence caused by genetic variation and crosstalks among subgenomes of the allohexaploid bread wheat (Triticum aestivum. L., BBAADD) is hypothesized to increase its adaptability and/or plasticity. However, the molecular basis of expression divergence remains unclear. Squamosa promoter-binding protein-like (SPL) transcription factors are critical for a wide array of biological processes. In this study, we constructed expression regulatory networks by combining DAP-seq for 40 SPLs, ATAC-seq, and RNA-seq. Our findings indicate that a group of low-affinity SPL binding regions (SBRs) were targeted by diverse SPLs and caused different sequence preferences around the core GTAC motif. The SBRs including the low-affinity ones are evolutionarily conserved, enriched GWAS signals related to important agricultural traits. However, those SBRs are highly diversified among the cis-regulatory regions (CREs) of syntenic genes, with less than 8% SBRs coexisting in triad genes, suggesting that CRE variations are critical for subgenome differentiations. Knocking out of TaSPL7A/B/D and TaSPL15A/B/D subfamily further proved that both high- and low-affinity SBRs played critical roles in the differential expression of genes regulating tiller number and spike sizes. Our results have provided baseline data for downstream networks of SPLs and wheat improvements and revealed that CRE variations are critical sources for subgenome divergence in the allohexaploid wheat.
Project description:Divergence of gene function is a hallmark of evolution, but assessing functional divergence over deep time is not trivial. The few alleles available for cross-species studies often fail to expose the entire functional spectrum of genes, potentially obscuring deeply conserved pleiotropic roles. Here, we explore the functional divergence of WUSCHEL HOMEOBOX9 (WOX9), suggested to have species-specific roles in embryo and inflorescence development. Using a cis-regulatory editing drive system, we generated a comprehensive allelic series in tomato, which revealed hidden pleiotropic roles for WOX9. Analysis of accessible chromatin and conserved cis-regulatory sequences identified the regions responsible for this pleiotropic activity, the functions of which were conserved in groundcherry, a tomato relative. Mimicking these alleles in arabidopsis, distantly related to tomato and groundcherry, revealed new inflorescence phenotypes, exposing a deeply conserved pleiotropy. We suggest that targeted cis-regulatory mutations can uncover conserved gene functions and reduce undesirable effects in crop improvement.
Project description:Wheat (Triticum aestivum) has a large allohexaploid genome. Subgenome-divergent regulation contributed to genome plasticity and the domestication of polyploid wheat. However, the specificity encoded in the wheat genome determining subgenome-divergent spatio-temporal regulation has been largely unexplored. The considerable size and complexity of the genome are major obstacles to dissecting the regulatory specificity. Here, we compared the epigenomes and transcriptomes from a large set of samples under diverse developmental and environmental conditions. Thousands of distal epigenetic regulatory elements (distal-epiREs) were specifically linked to their target promoters with coordinated epigenomic changes. We revealed that subgenome-divergent activity of homologous regulatory elements are affected by specific epigenetic signatures. Subgenome-divergent epiRE regulation of tissue specificity is associated with dynamic modulation of H3K27me3 mediated by Polycomb complex and demethylases. Furthermore, quantitative epigenomic approaches detected key stress responsive cis- and trans-acting factors validated by DNA Affinity Purification and sequencing (DAP-seq), and demonstrated the coordinated interplay between epiRE sequence contexts, epigenetic factors, and transcription factors in regulating subgenome divergent transcriptional responses to external changes. Thus, this study provides a wealth of resources for elucidating the epiRE regulomics and subgenome-divergent regulation in hexaploid wheat, and gives new clues for interpreting genetic and epigenetic interplay in regulating the benefits of polyploid wheat.
Project description:Expression divergence caused by genetic variation and crosstalks among subgenomes of the allohexaploid bread wheat (Triticum aestivum. L., BBAADD) is hypothesized to increase its adaptability and/or plasticity. However, the molecular basis of expression divergence remains unclear. Squamosa promoter-binding protein-like (SPL) transcription factors are critical for a wide array of biological processes. In this study, we constructed expression regulatory networks by combining DAP-seq for 40 SPLs, ATAC-seq, and RNA-seq. Our findings indicate that a group of low-affinity SPL binding regions (SBRs) were targeted by diverse SPLs and caused different sequence preferences around the core GTAC motif. The SBRs including the low-affinity ones are evolutionarily conserved, enriched GWAS signals related to important agricultural traits. However, those SBRs are highly diversified among the cis-regulatory regions (CREs) of syntenic genes, with less than 8% SBRs coexisting in triad genes, suggesting that CRE variations are critical for subgenome differentiations. Knocking out of TaSPL7A/B/D and TaSPL15A/B/D subfamily further proved that both high- and low-affinity SBRs played critical roles in the differential expression of genes regulating tiller number and spike sizes. Our results have provided baseline data for downstream networks of SPLs and wheat improvements and revealed that CRE variations are critical sources for subgenome divergence in the allohexaploid wheat.
Project description:Expression divergence caused by genetic variation and crosstalks among subgenomes of the allohexaploid bread wheat (Triticum aestivum. L., BBAADD) is hypothesized to increase its adaptability and/or plasticity. However, the molecular basis of expression divergence remains unclear. Squamosa promoter-binding protein-like (SPL) transcription factors are critical for a wide array of biological processes. In this study, we constructed expression regulatory networks by combining DAP-seq for 40 SPLs, ATAC-seq, and RNA-seq. Our findings indicate that a group of low-affinity SPL binding regions (SBRs) were targeted by diverse SPLs and caused different sequence preferences around the core GTAC motif. The SBRs including the low-affinity ones are evolutionarily conserved, enriched GWAS signals related to important agricultural traits. However, those SBRs are highly diversified among the cis-regulatory regions (CREs) of syntenic genes, with less than 8% SBRs coexisting in triad genes, suggesting that CRE variations are critical for subgenome differentiations. Knocking out of TaSPL7A/B/D and TaSPL15A/B/D subfamily further proved that both high- and low-affinity SBRs played critical roles in the differential expression of genes regulating tiller number and spike sizes. Our results have provided baseline data for downstream networks of SPLs and wheat improvements and revealed that CRE variations are critical sources for subgenome divergence in the allohexaploid wheat.