An official website of the United States government
Centromeres are essential for chromosome function, yet their role in shaping genome evolution in polyploid plants remains poorly understood. Allopolyploidy, where post-hybridization genome doubling merges parental genomes that may differ markedly in chromosomal architecture, has the potential to increase centromeric complexity and influence genomic plasticity. We explore this possibility in carnivorous Caryophyllales, a morphologically and chromosomally diverse plant lineage encompassing sundews, Venus flytraps, and Nepenthes pitcher plants. Focusing on sundews (Drosera), we generated chromosome-scale assemblies of holocentric D. regia and monocentric D. capensis, which share an allohexaploid origin but have diverged dramatically in genome structure. D. regia retains ancestral chromosomal fusions, dispersed centromeric repeats, and conserved synteny, whereas D. capensis exhibits extensive chromosomal reorganization and regionally localized centromeres after a lineage-specific genome duplication. Phylogenomic evidence traces D. regia to an ancient hybridization between sundew- and Venus flytrap-like ancestors, setting it apart within its infrageneric context. Genus-wide satellite DNA repeat profiling reveals rapid turnover and species-level variation in centromere organization. Together, these results establish sundews as a natural system for investigating how centromere dynamics interact with recurrent polyploidization and episodes of ecological innovation to shape genomic resilience.
more »
« less
Dramatic difference in rate of chromosome number evolution among sundew ( Drosera L., Droseraceae) lineages
Abstract Chromosome number change is a driver of speciation in eukaryotic organisms. Carnivorous sundews in the plant genus Drosera L. exhibit single chromosome number variation both among and within species, especially in the Australian Drosera subg. Ergaleium D.C., potentially linked to atypical centromeres that span much of the length of the chromosomes. We critically reviewed the literature on chromosome counts in Drosera, verified the taxonomy and quality of the original counts, and reconstructed dated phylogenies. We used the BiChrom model to test whether rates of single chromosome number increase and decrease, and chromosome number doubling differed between D. subg. Ergaleium and the other subgenera and between self-compatible and self-incompatible lineages. The best model for chromosome evolution among subgenera had equal rates of chromosome number doubling but higher rates of single chromosome number change in D. subg. Ergaleium than in the other subgenera. Contrary to expectation, self-incompatible lineages had a significantly higher rate of single chromosome loss than self-compatible lineages. We found no evidence for an association between differences in single chromosome number changes and diploidization after polyploidy or centromere type. This study presents an exemplar for critically examining published cytological data and rigorously testing factors that may impact the rates of chromosome number evolution.
more »
« less
- Award ID(s):
- 2015210
- PAR ID:
- 10546793
- Editor(s):
- Chapman, Tracey
- Publisher / Repository:
- Oxford
- Date Published:
- Journal Name:
- Evolution
- Volume:
- 77
- Issue:
- 10
- ISSN:
- 0014-3820
- Page Range / eLocation ID:
- 2314 to 2325
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Sloan, Daniel (Ed.)While mitochondrial genome content and organization is quite diverse across all Eukaryotes, most bilaterian animal mitochondrial genomes (mitogenomes) exhibit highly conserved gene content and organisation, with genes typically encoded on a single circular chromosome. However, many species of parasitic lice (Insecta: Phthiraptera) are among the notable exceptions, having mitogenomes fragmented into multiple circular chromosomes. To better understand the process of mitogenome fragmentation, we conducted a large-scale genomic study of a major group of lice, Amblycera, with extensive taxon sampling. Analyses of the evolution of mitogenome structure across a phylogenomic tree of 90 samples from 53 genera revealed evidence for multiple independent origins of mitogenome fragmentation, some inferred to have occurred less than five million years ago. We leveraged these many independent origins of fragmentation to compare the rates of DNA substitution and gene rearrangement, specifically contrasting branches with fragmented and non-fragmented mitogenomes. We found that lineages with fragmented mitochondrial genomes had significantly higher rates of mitochondrial sequence evolution. In addition, lineages with fragmented mitochondrial genomes were more likely to have mitogenome gene rearrangements than those with single-chromosome mitochondrial genomes. By combining phylogenomics and mitochondrial genomics we provide a detailed portrait of mitogenome evolution across this group of insects with a remarkably unstable mitogenome structure, identifying processes of molecular evolution that are correlated with mitogenome fragmentation.more » « less
-
Summary The effects of single chromosome number change—dysploidy – mediating diversification remain poorly understood. Dysploidy modifies recombination rates, linkage, or reproductive isolation, especially for one‐fifth of all eukaryote lineages with holocentric chromosomes. Dysploidy effects on diversification have not been estimated because modeling chromosome numbers linked to diversification with heterogeneity along phylogenies is quantitatively challenging.We propose a new state‐dependent diversification model of chromosome evolution that links diversification rates to dysploidy rates considering heterogeneity and differentiates between anagenetic and cladogenetic changes. We apply this model toCarex(Cyperaceae), a cosmopolitan flowering plant clade with holocentric chromosomes.We recover two distinct modes of chromosomal evolution and speciation inCarex. In one diversification mode, dysploidy occurs frequently and drives faster diversification rates. In the other mode, dysploidy is rare, and diversification is driven by hidden, unmeasured factors. When we use a model that excludes hidden states, we mistakenly infer a strong, uniformly positive effect of dysploidy on diversification, showing that standard models may lead to confident but incorrect conclusions about diversification.This study demonstrates that dysploidy can have a significant role in speciation in a large plant clade despite the presence of other unmeasured factors that simultaneously affect diversification.more » « less
-
Abstract Polyploidy occurs across the tree of life and is especially common in plants. Because newly formed cytotypes are often incompatible with their progenitors, polyploidy is also said to trigger “instantaneous” speciation. If a polyploid can self-fertilize or reproduce asexually, it is even possible for one individual to produce an entirely new lineage, but how often this scenario occurs is unclear. Here, we investigate the evolutionary history of the wild allotetraploid Mimulus sookensis, which was formed through hybridization between self-compatible, diploid species in the Mimulus guttatus complex. We generate a chromosome-scale reference assembly for M. sookensis and define its distinct subgenomes. Despite previous reports suggesting multiple origins of this highly selfing polyploid, we discover patterns of population genomic variation that provide unambiguous support for a single origin. One M. sookensis subgenome is clearly derived from the selfer Mimulus nasutus, which organellar variation suggests is the maternal progenitor. The ancestor of the other subgenome is less certain, but it shares variation with both Mimulus decorus and M. guttatus, two outcrossing diploids with geographic ranges that overlap broadly with M. sookensis. This study establishes M. sookensis as an example of instantaneous speciation, likely facilitated by the polyploid’s predisposition to self-fertilize.more » « less
-
Premise of research. Polyploidy, a major evolutionary process in flowering plants, is expected to 19 impact floral traits which can have cascading effects on pollination interactions, but this may 20 depend on selfing propensity. In a novel use of herbarium specimens, we assessed the effects of 21 polyploidy and mating system on floral traits and the pollination niche of 40 Brassicaceae 22 species. 23 Methodology. We combined data on mating system (self-compatible or self-incompatible) with 24 inferred ploidy level (polyploid or diploid) and use phylogenetically controlled analyses to 25 investigate their influence on floral traits (size and shape) and the degree of pollination 26 generalism based on the frequency and the richness of heterospecific pollen morphospecies 27 captured by stigmas. 28 Pivotal Results. Flower size (but not shape) depended on the interaction between ploidy and 29 mating system. Self-incompatible polyploid species had larger flowers than self-incompatible 30 diploids but there was no difference for self-compatible species. The breadth of pollination niche 31 (degree of generalism) was not affected by ploidy but rather strongly by mating system only. 32 Self-incompatible species had more stigmas with heterospecific pollen and higher heterospecific 33 pollen morphospecies richness per stigma than self-compatible species, regardless of their 34 ploidy. 35 Conclusions. Our results demonstrate that mating system moderated the influence of ploidy on 36 morphological features associated with pollination generalism but that response in terms of 37 heterospecific pollen captured as a proxy of pollination generalism was more variable.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1093/evolut/qpad153
