The origin of polyploid genomes of bluegrasses Poa L. and gene flow between Northern Pacific and sub-Antarctic islands

The involvement of present-day diploid bluegrass species in the formation of polyploid genomes was investigated using comparison of sequences of internal transcribed spacers ITS1 and ITS2, and the 5.8S rDNA sequence. It was demonstrated that highly polyploid New Zealand bluegrasses, P. cita (2n = 84; ca. 96 to 100), P. chathamica (2n = 112), and P. litorosa (2n = 263 to 266) formed separate highly supported clade together with tetraploids (2n = 28) P. intrusa, P. anceps, and P. trioides (Austrofestuca littoralis). Among the diploid species (2n = 14), the closest relatives of these species, as well as of the polyploid species of section Poa, are the genomes of Eurasian species P. remota, P. chaixcii (sect. Homalopoa), P densa (Bolbophorum), and P. sibirica (sect. Macropoa). Nuclear genomes of polyploid Stenopoa, Tichopoa, Oreinos, and Secundae are definitely related to the genome of Arctic species P. pseudabbreviata (sect. Abbreviatae). On the contrary, judging by the genes for nuclear 45S rRNA, genomes of diploid P. trivialis (sect. Pandemos), P. annua, and P. supina (sect. Ochlopoa both) are only remotely related to the genomes of highly polyploid species (distances p between them and other bluegrass species from different sections of subgenus Poa constitute 6-10% and 11-15%, respectively). The conclusion on the relationships between highly polyploid and diploid bluegrass species was tested using analysis of synapomorphic mutations in the 5.8S rRNA gene. It was demonstrated that genomes of Poa eminens (2n = 42) and P. schischkinii (2n = 70) (sect. Arctopoa both) were noticeably different in ITS regions from the genomes of the members of the type subgenus Poa. A comparison of the Arctopoa ITS regions showed that the differences between them constituted only 0.2%. At the same time, p distances between the Arctopoa ITS and those from the species belonging to other sections of the genus Poa varied from 5 to 14%. South American species P chonotica (sect. Andinae) (=Ncoraepoa chonotica) (2n = 42) was found to be related to Arctagrostis, Festucella, and Hookerochloa, being at the same time quite distant from the other species of the genus Poa. Polymorphic in chromosome number highly polyploid species of Northern Hemisphere, P. arctica (2n = 42 to 106), P. turneri (2n = 42, 63 to 64), and P. smirnovii (2n = 42, 70) (sect. Malacanthae) are relative to a large group of tetraploid (2n = 28) endemic bluegrass species from New Zealand and sub-Antarctic islands (P. novae-zelandiae and allied species).     

Chromosome numbers and their taxonomic implications in the genusPoa of Japan

As part of the work leading to a taxonomic revision ofPoa of Japan, chromosome numbers of nearly all indigenous species of JapanesePoa, together with those of some putative interspecific hybrids, were examined. The following chromosome numbers were found:Poa annua, 2n=28;P. crassinervis, 2m=28;P. acroleuca, 2n=28;P. hisauchii, 2n=28;P. nipponica, 2n=28;P. crassinervis, 2n=28;P. acroleuca, 2n=35;P. tuberifera, 2n=28;P. fauriei, 2n=28;P. radula, 2n=42;P. hakusanensis, 2n=70;P. hayachinensis, 2n=42;P. malacantha var.shinanoana, 2n=63≈98;P. yatsugatakensis, 2n=ca. 71≈74, 77;P. sachalinensis, 2n=63, ca. 64, ca. 74;P. matsumurae, 2n=28;P. ogamontana, 2n=42;P. sphondylodes, 2n=28;P. viridula, 2n=42, 49, 56;P. nemoralis, 2n=70;P. glauca, 2n=42, 49, 56;P. eminens, 2n=42. It became clear that information obtained from chromosome counts is quite helpful in clarifying species boundaries in several species aggregates, such as thePoa acroleuca-hisauchii-nipponica aggregate. Results of the examination of morphological features of the voucher specimens in various species aggregates with taxonomic difficulties were reported, and the needs of some amendments for the species delimitation appearing in current floristic manuals were pointed out. A summary of chromosome counts so far made for JapanesePoa was tabulated. ThePoa flora of Japan characteristically lacked diploid plants.     

Taxonomy of the Poa laxa group,including two new taxa from Arctic Canada and Greenland,and Oregon,and a re‐examination of P. sect. Oreinos (Poaceae)

The Poa laxa Haenke species group, comprising four alpine–arctic taxa in P. sect. Oreinos, has a complicated and confusing taxonomic history. Here we re‐examine the taxonomy of the group and section based on sequences of three plastid and two nuclear ribosomal DNA markers. Poa laxa s.l. resolved in a clade with species of sections Abbreviatae, Oreinos, Stenopoa, and Tichopoa. In the plastid analyses, Poa laxa s.s. (type of sect. Oreinos) was placed in a subclade with P. glauca and other sect. Stenopoa species, while all other P. laxa s.l. taxa were placed in a subclade with species of sect. Abbreviatae. We maintain P. laxa s.s. (mainly 2n = 28) of west–central Europe in sect. Oreinos, while the other P. laxa s.l. taxa from northern Europe and North America (all 2n = 42 or higher ploid) are referred to P. sect. Abbreviatae. In North America only one collection of the northern European P. flexuosa subsp. flexuosa is accepted (Greenland, Jensen's Nunatakker), and P. flexuosa subsp. fernaldiana is accepted based on populations in eastern Canada and northeast USA. A new subspecies, P. flexuosa subsp. consauliae, is described from eastern Arctic Canada and Greenland; its variable morphological characteristics suggest introgression with P. glauca and it is predicted to be apomictic. Rocky Mountain P. laxa subsp. banffiana is treated as P. banffiana. Oregon material formerly considered to belong to P. laxa s.l. is named P. wallowensis. Poa sect. Oreinos is thus found to be polyphyletic, and is here emended to comprise only three continental European species, including P. laxa. Lectotypes are designated for P. aspera var. laxiuscula, P. fernaldiana, P. flexuosa, and P. laxa var. debilior. New chromosome numbers are reported for P. flexuosa subsp. consauliae (ca 2n = 42), and P. glauca (2n = 63) from Baffin Island. A key to the species and subspecies found in North America is given.     

Genome composition and origin of the polyploid Aegean grass Avenula agropyroides (Poaceae)

Aim The Aegean is a hotspot of plant biodiversity, with its island biota harbouring a large number of endemic taxa. To investigate the relationship between biogeography, polyploid speciation and genomics in the Aegean we used the biogeographically isolated highly polyploid eastern Mediterranean grass species Avenula agropyroides (2n = 70) as an example of complicated polyploid origin. Location Mediterranean, Aegean. Methods To clarify the origin of A. agropyroides, we conducted chromosome studies using repetitive DNAs as hybridization probes in fluorescent in situ hybridization experiments, chromosome banding methods and DNA sequence analyses of plasmid‐cloned nuclear ribosomal (nr) ITS1–5.8S–ITS2 DNA. Results Decaploid A. agropyroides had near‐autopolyploid karyotype structure and contained characteristic sequence motifs of nrDNA repeats not encountered in any of the diploids studied. Special repeat types found in one of its accessions (Crete) showed that A. agropyroides originated from a diploid species with a hybrid background. One of the genomes involved was close to both that of extant species (Avenula aetolica, Avenula compressa, Avenula hookeri, Avenula schelliana, Avenula versicolor) distributed mostly in the eastern Mediterranean to Asia and North America and also to the west Mediterranean (Avenula bromoides). The other resembled that of exclusively western Mediterranean species (Avenula albinervis, Avenula levis, Avenula marginata, Avenula sulcata). Main conclusions Avenula agropyroides represents a remarkable polyploid in the eastern Mediterranean, conserving the genome structure of a diploid species that no longer exists. This highlights how the Aegean has been less affected than other Eurasian regions by the repeated shifts of climatic zones and vegetation belts since the Late Tertiary.     

Phylogenetic relationships and character evolution in Primula L.: The usefulness of ITS sequence data

ABSTRACT

The main goals of this research were to reconstruct the infrageneric phylogeny of the genus Primula based on both nuclear and chloroplast DNA sequences, and to use the resulting phylogenies to elucidate the evolution of breeding systems, morphological characters, chromosome number, and biogeographic distribution in the genus. In this paper, the results of a pilot study based on the nuclear ribosomal Internal Transcribed Spacer (ITS) region are described. ITS sequences from 21 taxa produced a number of variable characters sufficient to resolve relationships among sections. The resulting phylogeny confirmed the monophyly of sections Auricula and Aleuritia. Sections Armerina, Proliferae, Crystallophlomis, Parryi, and Auricula, with a base chromosome number of x = 11, and sect. Aleuritia, with a base chromosome number of x = 9, formed two well supported clades. The ITS topology also suggested that leaves with revolute vernation, previously believed to be a derived state, might represent the ancestral condition in Primula, with later reversals to the involute condition. Finally, this initial ITS tree provides preliminary support to the proposed role of the widespread, diploid and heterostylous P. mistassinica as having given origin to the polyploid, homostylous P. incana and P. laurentiana.     

A review of chromosome cytology in Hyacinthaceae subfamily Ornithogaloideae (Albuca, Dipcadi, Ornithogalum and Pseudogaltonia) in sub-Saharan Africa

The chromosome cytology of Hyacinthaceae subfamily Ornithogaloideae is reviewed within the framework of a recent molecular-based classification, with particular emphasis on its center of diversity in sub-Saharan Africa. We also provide new chromosome counts for sections that are unknown or poorly known cytologically. Albuca subgen. Namibiogalum (9 spp.) probably has an ancestral base number of x = 10 but subgen. Albuca (± 70 spp), subgen. Monarchos (9 spp.) and subgen. Osmyne (36 spp.) have x = 9. The pattern in subgen. Urophyllon (3 spp.) is remarkable: although x = 6 is likely, the species in the section exhibit a range of 2n = 12, 10, 8, 6 and 4 (exclusive of polyploidy). All karyotypes have three large chromosome pairs and a variable number of small chromosomes. Pseudogaltonia (2 spp.) has x = 9 and Dipcadi (26 spp.) possibly x = 9 in series Uropetalum and x = 6 in series Dipcadi, which exhibits a pattern of descending dysploidy leading to n = 3 in D. marlothii. In Ornithogalum (± 130 spp.) chromosome numbers are known for only 24 of the ± 84 sub-Saharan species, mostly from subgen. Aspasia and subgen. Ornithogalum sect. Linaspasia, both of which have x = 6, and from subgen. Galtonia, which has x = 8. In contrast, x = 7 is basic for the Eurasian sects. Honorius and Melophis, and x = 18 seems likely for sect. Cathissa. Sect. Ornithogalum, the cytology of which we does not examine in detail, may have x = 9. Polyploidy is apparently rare in the sub-Saharan African ornithogaloids, in marked contrast to the high frequency of polyploidy among Eurasian species. In Albuca just 3 or possibly 4 sub-Saharan species (9% or 13% of those counted) are exclusively polyploid and 5 more have diploid and polyploid races; and in sub-Saharan Ornithogalum, only the tropical O. gracillimum is exclusively polyploid, and the western southern African O. hispidum has diploid and polyploid races.     

On polyphyly of the former section Ochlopoa and the hybridogenic section Acroleucae (Poa,Poaceae): insights from molecular phylogenetic analyses

In this study, sequence data from the inert nuclear region ITS1‐5.8S rDNA‐ITS2 and the chloroplast region trnL–F, as well as a few morphological characters, are analysed to the relationships among known annual Poa (bluegrasses). It is shown that all taxa from the Poa annua aggregate distinguished by lemma characters and growth form have identical ITS and trnL–trnF sequences, all ITS sequences of this aggregate are the same as thethose of P. supina, and all trnL–trnF sequences are homologous with those of P. infirma. Furthermore, no differences were found between unusual morphotypes of P. supina with short spinules on their panicle branches and typical plants, but Siberian samples were found to have a slightly differentiated trnL–trnF region. These results suggest a hybrid origin of the Asian annual bluegrasses. Their maternal genome is close to that of P. sect. Homalopoa, but their ITS sequences are different. Some ITS sequences from annual Asian bluegrasses are resolved among representatives of P. sect. Stenopoa while for other (morphologically closely similar) species they fall in a clade with representatives of P. sect. Malacanthae. The latter group is distant from P. sect. Ochlopoa and is better treated as a separate section, viz P. sect. Acroleucae. The American annual bluegrasses are heterogeneous and also rather distant from P. sect. Ochlopoa. Poa chapmaniana, a species with cleistogamic flowers, is nested among the basal Subantarctic sections, far away from the taxa with which it has previously been considered related. It is indeed closer to P. sect. Ochlopoa than to other annual American bluegrasses. Thus, the studied annual species in fact belong to four independent evolutionary lines (or six including the separate genus Eremopoa and the Turkish Poa jubata), one of which, Acroleucae, has gone through three reticulation events. As in previous studies, our analysis did not support the generic status of P. sect. Ochlopoa.     

Molecular characterization of vernalization loci VRN1 in wild and cultivated wheats

Background  

Variability of the VRN1 promoter region of the unique collection of spring polyploid and wild diploid wheat species together with diploid goatgrasses (donor of B and D genomes of polyploid wheats) were investigated. Accessions of wild diploid (T. boeoticum, T. urartu) and tetraploid (T. araraticum, T. timopheevii) species were studied for the first time.     

Evolution of Internal Transcribed Spacer Region of Nuclear Ribosomal DNA in Allopolyploids of Aegilops

Hybridization with subsequent polyploidy is a prominent process in evolution of higher plants, but few data address the evolution of homeologous sequences after polyploidy. The internal transcribed spacer (ITS) of nuclear ribosomal DNA (nrDNA) from eleven allopolyploid species in Aegilops was investigated by PCR amplification and direct sequencing. The sequences obtained were used to study the evolution of ITS region in allopolyploid species. The length of ITS region varied from 599 to 606 bp and the number of variable sites was 93, i.e. 51 and 42 for ITS1 and ITS2 re spectively. Some polymorphic sites were observed in polyploid species, and this indicated that the ancestral sequences had not been homogenized completely by concerted evolution. Distance matrix analysis of diploid and polyploid species by neighbor-joining method, using Triticum monococcum as outgroup, resulted in well-resolved neighbor-joining tree indicating that the ITS regions of UUMM and UUSS genome ( sect. Vertebrata) were homogenizing toward those of UU ancestal genome. This result is in agreement with the results of ctyogenetics of Aegilops. On the other hand, the neighbor joining tree including the D-genome group species (sect. Cylindropyrum and sect. Polyeides ) com prised three clades (CC-DDCC, UU-DDMM-DDMMSS-DDMMUU and MM-DDMvMv), which sug gested that concerted evolution was homogenizing the ITS region of the polyploid derivatives to either of their ancestors.     

Genetic relationships in hibiscus sect. Furcaria

The eighteen species studied form an allopolyploid series (x=18). The morphology, crossing behavior, and geographical distribution of 6 diploid, 9 tetraploid, 2 octoploid, and 1 decaploid species were studied. From over 26,500 crosses, 19 hybrid combinations and several derived allopolyploids and three-species hybrids were obtained. Chromosome pairing in the hybrids showed that a minimum of 6 and a maximum of 14 well-differentiated genome groups exist in sect. Furcaia, at least two of which appear to be confined to the Old World. No evidence was found that New World genomes are represented in the Old World. The primary radiation of the diploid genomes probably occurred at about the same time as that of the diploid genomes of Gossypium, whereas the tetraploids and one of the octoploid species (H. furcatus Roxb., non Willd.) seem to be of later origin (late Pleistocene or Recent). Octoploid H. diversifolius Jacq., a circumtropical species, may be a relict of a much earlier round of polyploid evolution.     

Chromosome number variation and polyploidy in the genus Echinocereus (Cactaceae)

Analyses of meiotic and mitotic chromosomes were undertaken in 16 taxa of Echinocereus belonging to 12 species and all seven taxonomic sections (sensu Taylor). Chromosome numbers are reported for the first time for eight taxa, and previously published chromosome counts are confirmed for the remaining eight. Both diploid and polyploid counts were obtained. Eleven (69%) of the taxa surveyed were diploid (2n = 22); the five varieties of E. engelmannii were polyploid (2n = 44). Overall, chromosome counts are available for 23 of the 48 proposed species (sensu Taylor). Of these, 19 (82%) are diploid, and four (18%) are polyploid. Polyploid cytotypes are most common in the primitive sections, e.g., sections Erecti and Triglochidiatus, which suggests that polyploidy is probably a derived condition in Echinocereus. Polyploid taxa range from medium to high latitudes and elevations relative to the overall distribution of the genus. Polyploidy, hybridization, and cryptic chromosomal rearrangements are thought to be the major causes of the speciation events of the genus.     

CYTOTAXONOMY OF CESPITOSE ZINNIAS

Torres , Andrew M. (U. Wisconsin, Milwaukee.) Cytotaxonomy of cespitose zinnias. Amer. Jour. Bot. 49(10): 1033–1037. Illus. 1962.—The results of hybridization studies among 5 of the 6 cespitose species of Zinnia are reported. Analyses of meiosis in the F₁ hybrids suggest there are 2 genomes, A and B, in the polyploid taxa. The A genome apparently exists in the diploid state in 2 species, but the B genome is known only from polyploid taxa. The chromosome number of Z. oligantha (2n = 20) is reported for the first time.     

New chromosome counts and evidence of polyploidy in Haageocereus and related genera in tribe Trichocereeae and other tribes of Cactaceae

Chromosome numbers for a total of 54 individuals representing 13 genera and 40 species of Cactaceae, mostly in tribe Trichocereeae, are reported. Five additional taxa examined belong to subfamily Opuntioideae and other tribes of Cactoideae (Browningieae, Pachycereeae, Notocacteae, and Cereeae). Among Trichocereeae, counts for 35 taxa in eight genera are reported, with half of these (17 species) for the genus Haageocereus. These are the first chromosome numbers reported for 36 of the 40 taxa examined, as well as the first counts for the genus Haageocereus. Both diploid and polyploid counts were obtained. Twenty nine species were diploid with 2n=2x=22. Polyploid counts were obtained from the genera Espostoa, Cleistocactus, Haageocereus, and Weberbauerocereus; we detected one triploid (2n=3x=33), nine tetraploids (2n=4x=44), one hexaploid (2n=6x=66), and three octoploids (2n=8x=88). In two cases, different counts were recorded for different individuals of the same species (Espostoa lanata, with 2n=22, 44, and 66; and Weberbauerocereus rauhii, with 2n=44 and 88). These are the first reported polyploid counts for Haageocereus, Cleistocactus, and Espostoa. Our counts support the hypothesis that polyploidy and hybridization have played prominent roles in the evolution of Haageocereus, Weberbauerocereus, and other Trichocereeae.     

The unique genome of two-chromosome grasses <Emphasis Type="Italic">Zingeria</Emphasis> and <Emphasis Type="Italic">Colpodium</Emphasis>, its origin,and evolution

Chromosome C-banding and two-color fluorescent in situ hybridization (FISH) were used to compare the chromosomes, to identify the chromosomal localization of the 45S and 5S rRNA genes, and to analyze the sequences of internal transcribed spacers 1 and 2 (ITS1 and ITS2) of the 45S rRNA genes in the genomes of grasses Zingeria biebersteiniana (2n = 4), Z. pisidica, Z. trichopoda (2n = 8), Colpodium versicolor (2n = 4), and Catabrosella variegata (syn. Colpodium variegatum) (2 n = 10). Differences in C-banding pattern were observed for two Z. biebersteiniana accessions from different localities. Similar C-banding patterns of chromosomes 1 and 2 were demonstrated for the Z. pisidica and Z. biebersteininana karyotypes. Chromosome C banding and localization of the 45S and 5S rRNA genes on the chromosomes of the two Zingeria species confirmed the assumption that Z. pisidica is an allotetraploid with one of the subgenomes similar to the Z. biebersteiniana genome. ITS comparisons showed that the unique two-chromosome grasses (x = 2)—Z. biebersteiniana (2n = 4), Z. trichopoda (2n = 8), Z. pisidica (2n = 8), and C. versicolor (2n = 4), which were earlier assigned to different tribes of subtribes of the family Poaceae—represent two closely related genera, the genetic distance (p-distance) between their ITSs being only 1.2–4.4%. The Zingeria species and C. versicolor formed a common clade with Catabrosella araratica (2n = 42, x = 7) on a molecular phylogenetic tree. Thus, the karyotypes of Zingeria and Colpodium, which have the lowest known basic chromosome number (x = 2), proved to be monophyletic, rather than originating from different phylogenetic lineages.     

Sequence variation in ITS spacers and 5.8S rDNA and relationship of E, St, P, Ns, Xm, and H genomes in the genera of Agropyron, Elytrigia, Leymus, Pascopyrum, Psathyrostachys, and Hordeum

Understanding species evolution and improvement requires information of their genome origin and differentiation. Among the species in the family Gramineae, genome identities of Agropyron-Elytrigia-Leymus group are still ambiguous. In order to delineate the genome relationship, nucleotide sequence analysis in the rDNA ITS regions was carried out among the species in the genera Elytrigia, Agropyron, Psathyrostachys, Leymus, and Psacopyrum containing E, St, P, Ns, and Xm genomes. The ITS-1 and ITS-2 showed a narrow range of variation in length except for the presence of a pentanucleotide, TGGGG, in/del in some haplotypes, whereas higher numbers of nucleotide substitutions were observed in most genera. There were 187 variable sites in the ITS-1, 5.8S, and ITS-2 regions, in which a few genome specific mutations were observed. While the level of variation was similar between ITS-1 and ITS-2, the rate of transition mutation versus transversion mutations was different among the ITS-1, 5.8S, and ITS-2 segments. GC contents of the ITS regions ranged between 55–65% between genomes and the haplotypes of P and H genomes were slightly higher than others. In phylogenetic analysis, the ITS haplotypes were classified into two groups; one containing H, Ns, NsXm genomes, and another containing P, St, and E genomes, which are congruous to the genome affinities from other studies. Among the four genomes in Pascopyrum smithii (2n=8x=56, StStNsNsHHXmXm), the haplotypes of H and St genomes were identified with the reference diploid species, but the haplotypes having Ns and Xm genomes were not found in the present analysis.     

Phylogenetic relationships among the species of <Emphasis Type="Italic">Elymus</Emphasis> sensu lato in Triticeae (Poaceae) based on nuclear rDNA ITS sequences

The genus Elymus L. sensu lato includes Roegneria, Elymus, Hystrix, Sitanion and Kengyilia, and they are very important group in the tribe Triticeae. However, the phylogenetic relationships and taxonomic status of them are still in dispute. The ITS sequences were obtained and analyzed for their phylogenetic relationships by using Maximum Parsimony (MP) and Bayesian Inference (BI) methods. The main results were as follows: (1) Most species in Roegneria, Elymus and Sitanion were clustered in the St clade with diploid St genome species, and it was difficult to distinguish the species in Roegneria and Elymus; (2) The polyploid species with St genomes in the St clade were divided into three groups, which suggests that there exists differentiation of St genome in polyploids; (3) Most species of Kengyilia have only P-type of clone and clustered with diploid Agropyron species, which may suggest that Kengyilia is a valid genus; (4) Hy. patula, the type species of Hystrix was clustered with species of Elymus, while Hy. duthiei ssp. duthiei, Hy. duthiei ssp. longearistata, Hy. coreana and Hy. komarovii were grouped with diploid Psathyrostachys species. It indicated that Hy. patula is distinct related to other Hystrix species, and it is reasonable to treat Hystrix patula as Elymus hystrix and other species in Hystrix should be transferred to Leymus; (5) The “clones bias” in ITS sequences are widespread in the allopolyploid species. The article is published in the original.     

Spatio‐temporal patterns of genome evolution in allotetraploid species of the genus Oryza

Despite knowledge that polyploidy is widespread and a major evolutionary force in flowering plant diversification, detailed comparative molecular studies on polyploidy have been confined to only a few species and families. The genus Oryza is composed of 23 species that are classified into ten distinct ‘genome types’ (six diploid and four polyploid), and is emerging as a powerful new model system to study polyploidy. Here we report the identification, sequence and comprehensive comparative annotation of eight homoeologous genomes from a single orthologous region (Adh1–Adh2) from four allopolyploid species representing each of the known Oryza genome types (BC, CD, HJ and KL). Detailed comparative phylogenomic analyses of these regions within and across species and ploidy levels provided several insights into the spatio‐temporal dynamics of genome organization and evolution of this region in ‘natural’ polyploids of Oryza. The major findings of this study are that: (i) homoeologous genomic regions within the same nucleus experience both independent and parallel evolution, (ii) differential lineage‐specific selection pressures do not occur between polyploids and their diploid progenitors, (iii) there have been no dramatic structural changes relative to the diploid ancestors, (iv) a variation in the molecular evolutionary rate exists between the two genomes in the BC complex species even though the BC and CD polyploid species appear to have arisen <2 million years ago, and (v) there are no clear distinctions in the patterns of genome evolution in the diploid versus polyploid species.     

Recent and recurrent polyploidy in Tragopogon (Asteraceae): cytogenetic, genomic and genetic comparisons

Tragopogon mirus Ownbey and T. miscellus Ownbey are allopolyploids that formed repeatedly during the past 80 years following the introduction of three diploids (T. dubius Scop., T. pratensis L. and T. porrifolius L.) from Europe to western North America. These polyploid species of known parentage are useful for studying the consequences of recent and recurrent polyploidization. We summarize recent analyses of the cytogenetic, genomic and genetic consequences of polyploidy in Tragopogon. Analyses of rDNA ITS (internal transcribed spacer) + ETS (external transcribed spacer) sequence data indicate that the parental diploids are phylogenetically well separated within Tragopogon (a genus of perhaps 150 species), in agreement with isozymic and cpDNA data. Using Southern blot and cloning experiments on tissue from early herbarium collections of T. mirus and T. miscellus (from 1949) to represent the rDNA repeat condition closer to the time of polyploidization than samples collected today, we have demonstrated concerted evolution of rDNA. Concerted evolution is ongoing, but has not proceeded to completion in any polyploid population examined; rDNA repeats of the diploid T. dubius are typically lost or converted in both allopolyploids, including populations of independent origin. Molecular cytogenetic studies employing rDNA probes, as well as centromeric and subtelomeric repeats isolated from Tragopogon, distinguished all chromosomes among the diploid progenitors (2n = 12). The diploid chromosome complements are additive in both allopolyploids (2n = 24); there is no evidence of major chromosomal rearrangements in populations of either T. mirus or T. miscellus. cDNA‐AFLP display revealed differences in gene expression between T. miscellus and its diploid parents, as well as between populations of T. miscellus of reciprocal origin. Approximately 5% of the genes examined in the allopolyploid populations have been silenced, and an additional 4% exhibit novel gene expression relative to their diploid parents. Some of the differences in gene expression represent maternal or paternal effects. Multiple origins of a polyploid species not only affect patterns of genetic variation in natural populations, but also contribute to differential patterns of gene expression and may therefore play a major role in the long‐term evolution of polyploids. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 82 , 485–501.     

A bicontinental origin of polyploid Australian/New Zealand Lepidium species (Brassicaceae)? Evidence from genomic in situ hybridization

Background and Aims

Incongruence between chloroplast and nuclear DNA phylogenies, and single additive nucleotide positions in internal transcribed spacer (ITS) sequences of polyploid Australian/New Zealand (NZ) Lepidium species have been used to suggest a bicontinental hybrid origin. This pattern was explained by two trans-oceanic dispersals of Lepidium species from California and Africa and subsequent hybridization followed by homogenization of the ribosomal DNA sequence either to the Californian (C-clade) or to the African ITS-type (A-clade) in two different ITS-lineages of Australian/NZ Lepidium polyploids.

Methods

Genomic in situ hybridization (GISH) was used to unravel the genomic origin of polyploid Australian/NZ Lepidium species. Fluorescence in situ hybridization (FISH) with ribosomal DNA (rDNA) probes was applied to test the purported ITS evolution, and to facilitate chromosome counting in high-numbered polyploids.

Key Results

In Australian/NZ A-clade Lepidium polyploids, GISH identified African and Australian/NZ C-clade species as putative ancestral genomes. Neither the African nor the Californian genome were detected in Australian/NZ C-clade species and the Californian genome was not detected in Australian/NZ A-clade species. Five of the eight polyploid species (from 7x to 11x) displayed a diploid-like set of rDNA loci. Even the undecaploid species Lepidium muelleriferdinandi (2n = 11x = 88) showed only one pair of each rDNA repeat. In A-clade allopolyploids, in situ rDNA localization combined with GISH corroborated the presence of the African ITS-type.

Conclusions

The nuclear genomes of African and Australian/NZ C-clade species were detected by GISH in allopolyploid Australian/NZ Lepidium species of the A-clade, supporting their hybrid origin. The presumed hybrid origin of Australian/NZ C-clade taxa could not be confirmed. Hence, it is assumed that Californian ancestral taxa experienced rapid radiation in Australia/NZ into extant C-clade polyploid taxa followed by hybridization with African species. As a result, A-clade allopolyploid Lepidium species share the Californian chloroplast type and the African ITS-type with the C-clade Australian/NZ polyploid and African diploid species, respectively.Key words: Lepidium, Brassicaceae, FISH, GISH, hybridization, polyploidy, long-distance dispersal, ITS, rDNA, Australia, New Zealand     

Phylogeny of the a genomes of wild and cultivated wheat species

Diploid species of the genus Triticum L. are its most ancient representatives and have the A genome, which was more recently inherited by all polyploid species. Studies of the phylogenetic relationships among diploid and polyploid wheat species help to identify the donors of elementary genomes and to examine the species specificity of genomes. In this study, molecular analysis of the variable sequences of three nuclear genes (Acc-1, Pgk-1, and Vrn-1) was performed for wild and cultivated wheat species, including both diploids and polyploids. Based on the sequence variations found in the genes, clear differences were observed among elementary genomes, but almost no polymorphism was detected within each genome in polyploids. At the same time, the regions of the three genes proved to be rather heterogeneous in the diploid species Triticum boeoticum Boiss., T. urartu Thum. ex Gandil., and T. monococcum L., thus representing mixed populations. A genome variant identical to the A genome of polyploid species was observed only in T. urartu. Species-specific molecular markers discriminating the diploid species were not found. Analysis of the inheritance of morphological characters also failed to identify a species-specific character for the three diploid wheat species apart from the hairy leaf blade type, described previously.