Molecular Genetic Features of Polyploidization and Aneuploidization Reveal Unique Patterns for Genome Duplication in Diploid Malus (original) (raw)
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Variation in nuclear DNA content in Malus species and cultivated apples
2005
The nuclear DNA content for a group of 40 Malus species and hybrids has been estimated using flow cytometry. Estimates of nuclear DNA content for this germplasm collection range from 1.45 pg for Malus fusca (diploid) to 2.57 pg for Malus ioensis (triploid). Among diploids, the nuclear (2C) DNA ranges from 1.45 pg for M. fusca to 1.68 pg for Malus transitoria. Among triploids, the nuclear (3C) DNA content ranges from 2.37 pg / 3C for Malus sikkimensis to 2.57 pg / 3C for M. ioensis. Given the complexity of the apple genome and its suggested allopolyploid origin, the results obtained in this study confirm earlier reports that polyploids can easily withstand the loss of a certain amount of DNA, and that there is a slight tendency towards diminished haploid nuclear DNA content with increased polyploidy.
Journal of The Faculty of Agriculture Kyushu University, 2012
To estimate the breeding behavior of aneuploid apple (Malus × domestica), twelve crosses were undertaken with twelve aneuploid accessions pollinated with diploid 'Hongro' apple. A 2x × 2x cross with 'Hongro' was also carried out as a control experiment for these aneuploid × diploid crosses. The pollinated aneuploid accessions exhibited relatively high fruit set rates. The apple fruit obtained from the pollinated aneuploid accessions contained less seeds per fruit than those from the 2x × 2x cross. The weight of seeds from the fruits of the pollinated aneuploid accessions was not related to the chromosome number of the aneuploid seed parent. Some of the seeds obtained from the pollinated aneuploid accessions failed to grow into seedlings. Metaphase figures of the root tip cells of seedlings derived from the pollinated aneuploid accessions showed that of 155 seedlings examined 115 were diploid, two were triploid and 38 were aneuploid. The chromosome number of the aneuploid seedlings ranged from 35 to 39, except for 48 chromosomes of one seedling. The seedlings with 35 (2n=2x+1) chromosomes appeared with the highest frequency of 15/38 (39.5%). The chromosome number of the aneuploid seedlings approached to the diploid (2n=34) level, or the number of aneuploid seedlings decreased with increase of chromosome numbers from 35 to 39.
Aneuploidy, a Source of Genetic Diversity for Fruit Species
V International Symposium on In Vitro Culture and Horticultural Breeding, 2006
Aneuploidy is reported among several plant species. Issued from openpollinated polyploid plants and from targeted breeding, most genotypes can be saved after embryo culture that prevents plant failure due to abortion and growth abnormalities respectively. Aneuploid apple material revealed genetically stable through in vitro axillary branching and crossable after ex vitro grafting. However, certain genetic variability occurred after adventitious budding, spontaneously inducing polyploidisation and cytochimerism. Some cytochimerical clones probably sectorial chimeras, reversed to genetically uniform aneuploids after subcultures by axillary branching. Multiapexing and adventitious budding applied to these chimeras led to the regeneration of new genotypes characterized by stable and uniform ploidy or aneuploidy and mixoploidy as well. Different ploidy patterns of regenerants resulted from the hormonal balance of the shoot induction medium. The combination of the aneuploidy with the techniques of in vitro regeneration led to create new genotypes with a limited genetic variability. These are currently used for genetic analysis and the production of seedless fruit. It appears obvious that with the use of specific molecular markers, this way of genetic improvement could support the progression of innovative breeding programs.
Canadian Journal of Botany, 2005
Hawthorns and medlars are closely related genera in Rosaceae subfamily Maloideae, whose taxonomy remains poorly understood. Gametophytic apomixis occurs in polyploids, and diploids are sexual out-crossers, so ploidy level is of great interest, but suitable material for chromosome counts is of limited availability each year. The promise of flow cytometry is that it permits rapid measurement of nuclear DNA amounts from most tissues, and ploidy level can be inferred if climatic and taxonomic differences do not interfere. Our DNA measurements cover most of the taxonomic series in Crataegus, adding cultivated and naturalized Eurasian plants to the many wild plants collected mainly from south-central Canada and the southeastern and northwestern United States. We found that some variation in DNA amount per genome copy distinguishes certain taxa, but ploidy-level estimates are at least as clear as the published chromosome counts, especially in the most common diploid-triploid-tetraploid range, and to the single published higher (hexaploid) chromosome count, we add evidence of pentaploids. By comparing ploidy evaluations to morphology, we hypothesize that both autopolyploidy and allopolyploidy contribute to the taxonomic complexity. We compared DNA amounts in Maloideae with those in Gillenia, a likely sister genus to the subfamily, which has a smaller chromosome number.
The Significance of Polyploidy for Bulbous Ornamentals: A Molecular Cytogenetic Assessment
Floriculture and Ornamental Biotechnology, 2012
Most of the bulbous crops, viz., Crocus, Narcissus, Tulipa, Alstroemeria and Lilium that are commercially important, share certain common characteristics. The present day cultivars are all derived from hybrids between distantly related species, and in almost all cases spontaneous polyploidization has played a prominent role and there is a tendency to replace diploids by polyploid cultivars. Molecular cytogenetic techniques such as genomic in situ hybridization (GISH) and fluorescence in situ hybridization (FISH), along with other techniques, have greatly facilitated our understanding of the modes of origins of polyploids. Because the bulbous crops generally have large chromosomes, the parental genomes, individual chromosomes, as well as intergenomic recombinant chromosomes, can be accurately identified in the interspecific hybrids and their backcross progenies. This enables an assessment of the potential genetic variation that might occur in the progenies as well as the extent of introgression. Although the superiority of polyploids as compared to their diploid parents is beyond doubt, the actual explanation for their superiority is still elusive. Of the several explanations, chromosome dosage, optimal amounts of 4C DNA values of the complements, heterozygosity and favourable gene interactions transmitted by the 2n gametes to polyploid progenies are some of the factors that might be considered at present. Undoubtedly, more studies on the bulbous ornamental crops using molecular techniques might be rewarding.
Advances in the study of polyploidy since Plant speciation
New Phytologist, 2003
Enormous strides have been made in the study of polyploidy over the last 20 yr. Here, we highlight some of these discoveries and note where our understanding of polyploid evolution has changed. Genetic and genomic studies have dramatically altered the polyploidy paradigm. The estimated frequency of polyploidy has increased, and it is now recognized that multiple origins are the rule for most polyploids. Likewise, autopolyploidy is much more common than traditionally maintained. Rapid genomic rearrangements, genomic downsizing, movement of genetic elements across genomes, and the movement of foreign genetic materials into the polyploid genome illustrate the complex dynamics of polyploid genomes. Following polyploidization, both genetic and epigenetic mechanisms may play an important role in altering gene expression. Ecological studies reveal that plant polyploidy can have profound effects on interactions with animal herbivores and pollinators and that polyploidy may trigger changes in the reproductive biology of a species. Despite the recent advances in our understanding of polyploid evolution, many exciting aspects remain under-investigated. Some of these include the consequences of genetic and genomic changes in natural polyploid populations, the physiological and ecological effects of polyploidy, and whether recurrent polyploidy prompts evolution to repeat itself.
Taxon, 2018
Apomixis is a form of asexual reproduction that consists in cloning through seeds. In Limonium (Plumbaginaceae) species present a pollen-stigma dimorphism linked to a sporophytic self-incompatibility system associated with sexual and/ or apomictic reproductive modes. Previous work in other genera suggests that the emergence of apomixis is associated with hybridization and/or polyploidy. In this study, our goal was to test the ability of diploid and tetraploid species to hybridize and to evaluate the variate outcomes from these crosses. To achieve this, sexual diploid (L. nydeggeri, L. ovalifolium) and facultative apomict tetraploid (L. binervosum, L. dodartii) plants from cultivated material, previously cytogenetically and reproductively characterized, were used for experimental intra-and interspecific crosses. Genome sizes, ploidy levels and morphology were examined in the resulting progenies. Results showed a high production of viable seeds in particular in plants from tetraploid × diploid (heteroploid) crosses. In these crosses, some seedlings exhibited pleiocotyly (tricotyl, tetracotyl), while others showed polyembryony. In both homoploid (diploid × diploid) and heteroploid (tetraploid × diploid) crosses, most of the offspring plants were morphologically and in their ploidy similar to the female receiver, although some morphological abnormalities were found. Molecular progeny tests using the nrDNA ITS1-ITS2 sequence demonstrated an astounding range of diploid offspring plants originated from diploid × diploid crosses that were either genetically similar or distinct from parental plants. Although in intraspecific crosses most of the resulting progeny was diploid, one triploid plant was formed. Moreover, in homoploid interspecific crosses, neopolyploids (two tetraploid plants) were produced. Progeny plants from heteroploid crosses always showed nrDNA ITS1-ITS2 sequences identical to the parental plant used as female receiver. In conclusion, diploid homoploid crosses presented genetically diverse offspring arising from sexual reproduction. By contrast, heteroploid crosses generated clonal, maternal (apomictic) offspring.
A look at polyploidy and plant breeding
Journal of Plant Science and Phytopathology
Polyploidization is a process that generates genetic variability and therefore one of the engines of biological evolution. Since polyploidization produces important changes in the phenotype, mainly an increase in the size of the organs (i.e.: flowers and fruits), it is also a very important and powerful tool for plant improvement. Despite its intense use in breeding programs for various species, very little is known so far about the nature of this phenomenon. This work presents a brief review of the results obtained by the use of this tool in plant breeding and also raises some reflections on its mechanism of action.
PLoS ONE, 2013
High throughput arrays for the simultaneous genotyping of thousands of single-nucleotide polymorphisms (SNPs) have made the rapid genetic characterisation of plant genomes and the development of saturated linkage maps a realistic prospect for many plant species of agronomic importance. However, the correct calling of SNP genotypes in divergent polyploid genomes using array technology can be problematic due to paralogy, and to divergence in probe sequences causing changes in probe binding efficiencies. An Illumina Infinium II whole-genome genotyping array was recently developed for the cultivated apple and used to develop a molecular linkage map for an apple rootstock progeny (M432), but a large proportion of segregating SNPs were not mapped in the progeny, due to unexpected genotype clustering patterns. To investigate the causes of this unexpected clustering we performed BLAST analysis of all probe sequences against the 'Golden Delicious' genome sequence and discovered evidence for paralogous annealing sites and probe sequence divergence for a high proportion of probes contained on the array. Following visual re-evaluation of the genotyping data generated for 8,788 SNPs for the M432 progeny using the array, we manually re-scored genotypes at 818 loci and mapped a further 797 markers to the M432 linkage map. The newly mapped markers included the majority of those that could not be mapped previously, as well as loci that were previously scored as monomorphic, but which segregated due to divergence leading to heterozygosity in probe annealing sites. An evaluation of the 8,788 probes in a diverse collection of Malus germplasm showed that more than half the probes returned genotype clustering patterns that were difficult or impossible to interpret reliably, highlighting implications for the use of the array in genome-wide association studies.