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1.
It is timely to re-examine the phenomenon of polyploidy in plants. Indeed, the power of modern molecular technology to provide new insights, and the impetus of genomics, make polyploidy a fit, fashionable and futuristic topic for review. Some historical perspective is essential to understand the meaning of the terms, to recognize what is already known and what is dogma, and to frame incisive questions for future research. Polyploidy is important because life on earth is predominantly a polyploid phenomenon. Moreover, civilization is mainly powered by polyploid food – notably cereal endosperm. Ongoing uncertainty about the origin of triploid endosperm epitomizes our ignorance about somatic polyploidy. New molecular information makes it timely to reconsider how to identity polyploids and what is a polyploid state. A functional definition in terms of a minimal genome may be helpful. Genes are known that can raise or lower ploidy level. Molecular studies can test if, contrary to dogma, the relationship between diploids and polyploids is a dynamic two-way system. We still need to understand the mechanisms and roles of key genes controlling ploidy level and disomic inheritance. New evidence for genome duplications should be compared with old ideas about cryptopolyploidy, and new views of meiosis should not ignore premeiotic genome separation. In practice, new knowledge about polyploidy will be most useful only when it reliably predicts which crops can be usefully improved as stable autopolyploids and which genomes combined to create successful new allopolyloids.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 82 , 411–423.  相似文献   

2.
Endogenous pararetroviruses (EPRVs) represent a new class of dispersed repetitive DNA in plants. The genomes of many Nicotiana species and other solanaceous plants are rich in EPRVs. Distinct EPRV families are present in N. sylvestris ( Ns ) and in N. tomentosiformis ( Nto ), the two diploid progenitors of allotetraploid N. tabacum . Nicotiana EPRVs represent an interesting type of repetitive sequence to analyse in polyploids because of their potential impact on plant fitness and the epigenetic architecture of plant genomes. The Ns EPRV family appears identical in N. sylvestris and N. tabacum , indicating little change has occurred in either species since polyploid formation. By contrast, the Nto EPRV family is larger in N. tomentosiformis than in N. tabacum , suggesting either preferential elimination from the polyploid genome or specific accumulation in the diploid genome following polyploidization. The lability of Nto EPRVs might be enhanced by a frequent association with gypsy retrotransposons. Although some EPRVs are probably benign, others are potentially pathogenic or, conversely, determinants of virus resistance. Normally quiescent EPRVs can be reactivated and cause symptoms of infection in hybrids of species that differ in their EPRV content. EPRVs that furnish immunity to the free virus exemplify the selective value of so-called 'junk' DNA. Variation in the abundance and distribution of EPRVs among related species can be useful in taxonomic and evolutionary studies.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 82 , 627–638.  相似文献   

3.
DNA C-values might be one of important indices in the evaluation of angiospermous invasiveness. To test this viewpoint, we compared DNA 1C-values and basic genome sizes in 3,676 angiosperms. The results suggest that: (1) the two nuclear values vary greatly among different groups, e.g., significantly higher in herbs than in trees, in monocots than in dicots, in perennials than in non-perennials; (2) the two nuclear values both have significant effects on plant invasiveness, especially in herbs, dicots, monocots, perennials, non-perennials, diploids, polyploids, Compositae, and Poaceae, while not significant in trees and Fabaceae. Similar to weeds, the two values in crops are low, which suggests that crops may commonly hold higher invasive potential; (3) to evaluate the invasiveness of a given species, the information about ploidy level is necessary, and for polyploids, basic genome sizes are more reliable. For the results suggest that the selection favors polyploids in weeds at least partly because of the downsizing of basic genome size along with polyploidization.  相似文献   

4.
5.
DNA content was estimated by flow cytometry in seventeen taxa from the Dilatata, Quadrifaria and Paniculata groups of Paspalum and five synthetic hybrids. Results were compared to known genome constitutions and phylogenetic relationships. DNA 2C-values ranged from 1.24 pg in diploid P. juergensii to 3.79 pg in a hexaploid biotype of P. dilatatum. The I genome of three Quadrifaria diploids is 1.2 to 1.5-fold larger than the J genome of P. juergensii (Paniculata). The 2C-values of the IIJJ tetraploids of the Dilatata group are lower than expected based on putative genome donors. Reduction of genome sizes could have occurred after the formation of the allopolyploids of the Dilatata group. The DNA content of all synthetic hybrids is in accordance with the sum of parental C-values. The interactions driving genome downsizing may operate differently during the transition from diploidy to polyploidy than on subsequent increases in ploidy level.  相似文献   

6.
Polyploidy and the sexual system: what can we learn from Mercurialis annua?   总被引:1,自引:0,他引:1  
The evolutionary success of polyploidy most directly requires the ability of polyploid individuals to reproduce and transmit their genes to subsequent generations. As a result, the sexual system (i.e. the mating system and the sex allocation of a species) will necessarily play a key role in determining the fate of a new polyploid lineage. The effects of the sexual system on the evolution of polyploidy are complex and interactive. They include both aspects of the genetic system, the genetic load maintained in a population and the ecological context in which selection takes place. Here, we explore these complexities and review the empirical evidence for several potentially important genetic and ecological interactions between ploidy and the sexual system in plants. We place particular emphasis on work in our laboratory on the European annual plant Mercurialis annua , which offers promising scope for detailed investigations on this topic. M. annua forms a polyploid complex that varies in its sexual system from dioecy (separate sexes) through androdioecy (males and hermaphrodites) to functional hermaphroditism.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 82 , 547–560.  相似文献   

7.
The study of genome size evolution in a phylogenetic context in related polyploid and diploid lineages can help us to understand the advantages and disadvantages of genome size changes and their effect on diversification. Here, we contribute 199 new DNA sequences and a nearly threefold increase in genome size estimates in polyploid and diploid Veronica (Plantaginaceae) (to 128 species, c. 30% of the genus) to provide a comprehensive baseline to explore the effect of genome size changes. We reconstructed internal transcribed spacer (ITS) and trnL‐trnL‐trnF phylogenetic trees and performed phylogenetic generalized least squares (PGLS), ancestral character state reconstruction, molecular dating and diversification analyses. Veronica 1C‐values range from 0.26 to 3.19 pg. Life history is significantly correlated with 1C‐value, whereas ploidy and chromosome number are strongly correlated with both 1C‐ and 1Cx‐values. The estimated ancestral Veronica 1Cx‐value is 0.65 pg, with significant genome downsizing in the polyploid Southern Hemisphere subgenus Pseudoveronica and two Northern Hemisphere subgenera, and significant genome upsizing in two diploid subgenera. These genomic downsizing events are accompanied by increased diversification rates, but a ‘core shift’ was only detected in the rate of subgenus Pseudoveronica. Polyploidy is important in the evolution of the genus, and a link between genome downsizing and polyploid diversification and species radiations is hypothesized. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 178 , 243–266.  相似文献   

8.
BACKGROUND: In studies looking at individual polyploid species, the most common patterns of genomic change are that either genome size in the polyploid is additive (i.e. the sum of parental genome donors) or there is evidence of genome downsizing. Reports showing an increase in genome size are rare. In a large-scale analysis of 3008 species, genome downsizing was shown to be a widespread biological response to polyploidy. Polyploidy in the genus Nicotiana (Solanaceae) is common with approx. 40 % of the approx. 75 species being allotetraploid. Recent advances in understanding phylogenetic relationships of Nicotiana species and dating polyploid formation enable a temporal dimension to be added to the analysis of genome size evolution in these polyploids. METHODS: Genome sizes were measured in 18 species of Nicotiana (nine diploids and nine polyploids) ranging in age from <200,000 years to approx. 4.5 Myr old, to determine the direction and extent of genome size change following polyploidy. These data were combined with data from genomic in situ hybridization and increasing amounts of information on sequence composition in Nicotiana to provide insights into the molecular basis of genome size changes. KEY RESULTS AND CONCLUSIONS: By comparing the expected genome size of the polyploid (based on summing the genome size of species identified as either a parent or most closely related to the diploid progenitors) with the observed genome size, four polyploids showed genome downsizing and five showed increases. There was no discernable pattern in the direction of genome size change with age of polyploids, although with increasing age the amount of genome size change increased. In older polyploids (approx. 4.5 million years old) the increase in genome size was associated with loss of detectable genomic in situ hybridization signal, whereas some hybridization signal was still detected in species exhibiting genome downsizing. The possible significance of these results is discussed.  相似文献   

9.
The parentage of polyploid Sorbus species in the British Isles was investigated using plastid DNA microsatellites. Four hundred and fifty-three samples from 30 taxa were screened using six microsatellite fragments, which gave 28 haplotypes. The haplotypes formed groups clearly related to the ancestral diploids Sorbus aria , Sorbus aucuparia , and Sorbus torminalis . Species in the Sorbus aria group all had Aria haplotypes (with the exception of one English S. aria ), species in the Sorbus anglica group had an Aucuparia haplotype, and species in the Sorbus latifolia group had a Torminalis haplotype. Sorbus intermedia had an Aucuparia haplotype. This indicated that the hybridization events that led to the formation of species in the S. anglica and S. latifolia groups usually did so with S. aria s.l . as the pollen-donating (paternal) parent. The polyploids S. anglica , Sorbus bristoliensis , Sorbus croceocarpa , Sorbus decipiens , Sorbus devoniensis , Sorbus hibernica , Sorbus lancastriensis , Sorbus leptophylla , Sorbus leyana , Sorbus minima , Sorbus rupicola , Sorbus subcuneata , Sorbus vexans , Sorbus whiteana , Sorbus wilmottiana , and three unnamed taxa may each be derived from a single maternal lineage. The polyploids Sorbus eminens , Sorbus porrigentiformis , and S. latifolia have multiple maternal lineages. The two primary diploid hybrids S . ×  thuringiaca and S . ×  vagensis have arisen many times independently.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 154 , 291–304.  相似文献   

10.
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