Project description:Speciation via interspecific or intergeneric hybridization and polyploidization triggers genomic responses Examination of small RNA of diploid Parent, Tetraploid parent, F1 hybrid and hexaploid amhiploid. Four pools of plants for each sample
Project description:Genome rearrangements are associated with eukaryotic evolutionary processes ranging from tumorigenesis to speciation. Such rearrangements are especially common following the shock of interspecific hybridization, and some of these could be expected to have strong selective value. To test this expectation we created de novo interspecific yeast hybrids between two diverged but largely syntenic species, Saccharomyces cerevisiae and S. uvarum, then experimentally evolved them under continuous ammonium limitation. We discovered that a characteristic interspecific genome rearrangement arose multiple times in independently evolved populations. We uncovered nine different breakpoints, all occurring in a ~1 kb region of chromosome 14, and all producing an “interspecific fusion junction” within the MEP2 gene coding sequence, such that the 5’ portion derives from S. cerevisiae and the 3’ portion derives from S. uvarum. In most cases the rearrangements altered both chromosomes, resulting in what can be considered to be an introgression of a several-kb region of S. uvarum into an otherwise intact S. cerevisiae chromosome 14, while the S. uvarum chromosome 14 experienced an interspecific reciprocal translocation at the same breakpoint within MEP2, yielding a chimaeric chromosome. The net result is the presence in the cell of two MEP2 fusion genes having identical breakpoints. Given that MEP2 encodes for a high-affinity ammonium permease, that MEP2 fusion genes arise repeatedly under ammonium-limitation, and that three independent evolved isolates carrying MEP2 fusion genes are each more fit than their common ancestor, the novel MEP2 fusion genes are very likely adaptive under ammonium limitation. Our results suggest that when homoploid hybrids form, the admixture of two genomes enables swift and otherwise unlikely evolutionary innovations. Furthermore, the architecture of the MEP2 rearrangement suggests a model for rapid introgression, a phenomenon seen in numerous eukaryotic phyla, that does not invoke repeated backcrossing to one of the parental species. Nomenclature: GSY86 TimeZeroInoculum = ancestral interspecific hybrid used to inoculate ammonium-limited chemostats into 3 replicate vessels A, B, C. 150gen = various single-clone isolates from 150 generations of evolutions from vessels A, B or C. 200gen = various isolates from 200 generations of evolutions from vessels A, B or C. Logical Set: Set of arrays organized by shared biological context, such as organism, tumors types, processes, etc.
Project description:The formation of new species is often a consequence of genetic incompatibilities accumulated between populations during allopatric divergence. When divergent taxa interbreed, these incompatibilities impact physiology and have a direct cost resulting in reduced hybrid fitness. Recent surveys of gene regulation in interspecific hybrids have revealed anomalous expression across large proportions of the genome, with 30-70% of all genes apparently misexpressed, mostly in the direction of down-regulation. However, since most of these studies have focused on pairs of species exhibiting high degrees of reproductive isolation, the association between regulatory disruption and reduced hybrid fitness prior to species formation remains unclear. Within the copepod species Tigriopus californicus, interpopulation hybrids show reduced fitness associated with mitochondrial dysfunction. Here we show that in contrast to studies of interspecific hybrids, only 1.2% of the transcriptome was misexpressed in interpopulation hybrids of T. californicus, and nearly 80% of misexpressed genes were overexpressed rather than underexpressed. Moreover, many of the misexpressed genes were components of functional pathways impacted by mitonuclear incompatibilities in hybrid T. californicus (e.g., oxidative phosphorylation and antioxidant response). We also show that the magnitude of hybrid misregulation is not dependent on levels of protein sequence divergence, even though the latter is correlated with expression divergence between parental populations. Our results suggest that hybrid breakdown at early stages of speciation may result from initial incompatibilities amplified by the cost of compensatory physiological responses.
Project description:Genome rearrangements are associated with eukaryotic evolutionary processes ranging from tumorigenesis to speciation. Such rearrangements are especially common following the shock of interspecific hybridization, and some of these could be expected to have strong selective value. To test this expectation we created de novo interspecific yeast hybrids between two diverged but largely syntenic species, Saccharomyces cerevisiae and S. uvarum, then experimentally evolved them under continuous ammonium limitation. We discovered that a characteristic interspecific genome rearrangement arose multiple times in independently evolved populations. We uncovered nine different breakpoints, all occurring in a ~1 kb region of chromosome 14, and all producing an “interspecific fusion junction” within the MEP2 gene coding sequence, such that the 5’ portion derives from S. cerevisiae and the 3’ portion derives from S. uvarum. In most cases the rearrangements altered both chromosomes, resulting in what can be considered to be an introgression of a several-kb region of S. uvarum into an otherwise intact S. cerevisiae chromosome 14, while the S. uvarum chromosome 14 experienced an interspecific reciprocal translocation at the same breakpoint within MEP2, yielding a chimaeric chromosome. The net result is the presence in the cell of two MEP2 fusion genes having identical breakpoints. Given that MEP2 encodes for a high-affinity ammonium permease, that MEP2 fusion genes arise repeatedly under ammonium-limitation, and that three independent evolved isolates carrying MEP2 fusion genes are each more fit than their common ancestor, the novel MEP2 fusion genes are very likely adaptive under ammonium limitation. Our results suggest that when homoploid hybrids form, the admixture of two genomes enables swift and otherwise unlikely evolutionary innovations. Furthermore, the architecture of the MEP2 rearrangement suggests a model for rapid introgression, a phenomenon seen in numerous eukaryotic phyla, that does not invoke repeated backcrossing to one of the parental species. Nomenclature: GSY86 TimeZeroInoculum = ancestral interspecific hybrid used to inoculate ammonium-limited chemostats into 3 replicate vessels A, B, C. 150gen = various single-clone isolates from 150 generations of evolutions from vessels A, B or C. 200gen = various isolates from 200 generations of evolutions from vessels A, B or C.
Project description:High plasticity of common wheat is attributed to the captured and polyploidization-promoted diversity. However, uncontrolled subgenome diversification can lead to hybrid conflict and dysgenesis, resulting in decreased diversity. How genomic diversity is maintained and interpreted to increase plasticity is unclear. By data-mining from the binding of 193 genome-wide trans-factors and genetic perturbations in common wheat, we identified LHP1 as a major regulator of subgenome-diversified defense genes, enhancer RNAs, and metabolite synthesis-related gene clusters via H3K27me3. Stripe rust infection leads to a global decrease in LHP1-mediated H3K27me3, deprivation of which enhances common wheat stripe rust resistance. We also revealed the consistency between subgenome diversity and population diversity, potentially promoted by LHP1, implying the recent diversification preferentially occurred in the captured subgenome-diversified regions regulated by LHP1. Thus, common wheat benefitted from multi-faced role of LHP1 in promoting sequence diversity and repressing subgenome-diversified defenses; this constraint is eliminated by pathogen infections, enabling timely release and fixation of favorable variations, conferring the evolutionary advantage and high plasticity of common wheat.
Project description:Nascent allohexaploid wheat may represent the initial genetic state for the evolution and domestication of common wheat, which arose by combining the AB genomes of tetraploid Triticum turgidum with the D genome from Aegilops tauschii and out-competed its parents in growth vigor and adaptability. To better understand the molecular basis for this success, we performed mRNA and small RNA expression analyses in three tissues of nascent allohexaploid wheat and its following generations, their progenitors, and Chinese Spring, with the assistance of newly released A and D genome sequences. We found that nonadditive expression was rare among protein-coding genes which exhibited profound parental expression level dominance, with genes of total homoeolog expression level in nascent allohexaploid progeny similar to their expression levels in T. turgidum functionally enriched for development and those to Ae. tauschii distinctively for adaptation. In contrast, miRNAs appeared to be sensitive to polyploidization, with nonadditively expressed miRNAs potentially involved in growth vigor and adaptation. Meanwhile, siRNAs may contribute to biased repression of D homoeolog, possibly due to increased siRNA density on transposable element (TE)-associated D homoeologs. Together, our data provide new insights into homoeolog regulatory mechanisms that may be essential to heterosis in nascent hexaploid wheat.
Project description:Polyploidization, the increase in genome copies, is considered a major driving force for speciation. We have recently provided the first direct in planta evidence for polyspermy induced polyploidization. Capitalizing on a novel sco1-based polyspermy assay, we here show that polyspermy can selectively polyploidize the egg cell, while rendering the genome size of the ploidy-sensitive central cell unaffected. This unprecedented result indicates that polyspermy can bypass the triploid block, which is an established postzygotic polyploidization barrier. In fact, we here show that most polyspermy-derived seeds are insensitive to the triploid block suppressor admetos. The robustness of polyspermy-derived plants is evidenced by the first transcript profiling of triparental plants and our observation that these idiosyncratic organisms segregate tetraploid offspring within a single generation. Polyspermy-derived triparental plants are thus comparable to triploids recovered from interploidy crosses. Our results expand current polyploidization concepts and have important implications for plant breeding.
Project description:Nascent allohexaploid wheat may represent the initial genetic state for the evolution and domestication of common wheat, which arose by combining the AB genomes of tetraploid Triticum turgidum with the D genome from Aegilops tauschii and out-competed its parents in growth vigor and adaptability. To better understand the molecular basis for this success, we performed mRNA and small RNA expression analyses in three tissues of nascent allohexaploid wheat and its following generations, their progenitors, and Chinese Spring, with the assistance of newly released A and D genome sequences. We found that nonadditive expression was rare among protein-coding genes which exhibited profound parental expression level dominance, with genes of total homoeolog expression level in nascent allohexaploid progeny similar to their expression levels in T. turgidum functionally enriched for development and those to Ae. tauschii distinctively for adaptation. In contrast, miRNAs appeared to be sensitive to polyploidization, with nonadditively expressed miRNAs potentially involved in growth vigor and adaptation. Meanwhile, siRNAs may contribute to biased repression of D homoeolog, possibly due to increased siRNA density on transposable element (TE)-associated D homoeologs. Together, our data provide new insights into homoeolog regulatory mechanisms that may be essential to heterosis in nascent hexaploid wheat. We performed mRNA and small RNA analyses in three tissues of nascent allohexaploid wheat and its following generations, their progenitors, and Chinese Spring.Among these samples, Samples 1-6 and 26-31, tetraploid progenitors; Samples 7-12 and 32-37, diploid progenitors; Samples 13-22 and 38-47, following generations; Samples 23-25 and 48-50, Chinese Spring.