BAC libraries of Triticum urartu, Aegilops speltoides and Ae. tauschii, the diploid ancestors of polyploid wheat

Triticum urartu, Aegilops speltoides and Ae. tauschii are respectively the immediate diploid sources, or their closest relatives, of the A, B and D genomes of polyploid wheats. Here we report the construction and characterization of arrayed large-insert libraries in a bacterial artificial chromosome (BAC) vector, one for each of these diploid species. The libraries are equivalent to 3.7, 5.4 and 4.1 of the T. urartu, Ae. speltoides, Ae. tauschii genomes, respectively. The predicted levels of genome coverage were confirmed by library hybridization with single-copy genes. The libraries were used to estimate the proportion of known repeated nucleotide sequences and gene content in each genome by BAC-end sequencing. Repeated sequence families previously detected in Triticeae accounted for 57, 61 and 57% of the T. urartu, Ae. speltoides and Ae. tauschii genomes, and coding regions accounted for 5.8, 4.5 and 4.8%, respectively.     

Amylase protein inhibitors and the role of Aegilops species in polyploid wheat speciation

Protein inhibitors extracted with water from seeds of Triticum and genetically related species were characterized according to their apparent molecular weights, electrophoretic mobilities and their specificities in inhibiting α-amylases from human saliva and Tenebrio molitor L. larvae. No detectable amylase inhibition activity was found in extracts from diploid wheats, whereas in all tetraploid and hexaploid wheats as well as in the Aegilops species tested we found several amylase inhibitor groups of different molecular weights. In each group, several inhibitor components slightly different in their electrophoretic mobilities, but identical in their inhibition behaviour toward amylases from different origins have been shown. Both from the qualitative and quantitative standpoints, amylase protein inhibitors from hexaploid wheats were the summation of those from tetraploid wheats plus the ones from Aegilops squarrosa. Amylase inhibitors from Aegilops speltoides largely differed from those extracted from tetraploid wheats as well as from all the amylase inhibitors described in plant seeds up to now. These results indicate a relevant homology between the amylase inhibitor coding genes of the D wheat genome and those of the D Aegilops genome and confirm that Ae. squarrosa is the donor of the whole D genome to hexaploid wheats. They also suggest that Ae. speltoides is not the donor of the B genome to polyploid wheats, although a not yet identified Aegilops species might be such a donor.     

RFLP-based analysis of three RbcS subfamilies in diploid and polyploid species of wheat

The RbcS multigene family of hexaploid (bread) wheat, Triticum aestivum (genome BBAADD), which encodes the small subunit of Rubisco, comprises at least 22 genes. Based on their 3′ non-coding sequences, these genes have been classified into four subfamilies (SFs), of which three (SF-2, SF-3 and SF-4) are located on chromosomes of homoeologous group 2 and one (SF-1) on homoeologous group 5. In the present study we hybridized three RbcS subfamily-specific probes (for SF-1, SF-2 and SF-3) to total DNA digested with four restriction enzymes and analyzed the RFLP patterns of these subfamilies in eight diploid species of Aegilops and Triticum, and in two tetraploid and one hexaploid species of wheat (the diploid species are the putative progenitors of the polyploid wheats). The three subfamilies varied in their level of polymorphism, with SF-2 being the most polymorphic in all species. In the diploids, the order of polymorphism was SF-2 > SF-3 > SF-1, and in the polyploids SF-2 > SF-1 > SF-3. The RbcS genes of the conserved SF-1 were previously reported to have the highest expression levels in all the wheat tissues studied, indicating a negative correlation between polymorphism and gene expression. Among the diploids, the species with the D and the S genomes were the most polymorphic and the A-genome species were the least polymorphic. The polyploids were less polymorphic than the diploids. Within the polyploids, the A genome was somewhat more polymorphic than the B genome, while the D genome was the most conserved. Among the diploid species with the A genome, the RFLP pattern of T. urartu was closer to that of the A genome of the common wheat cultivar Chinese Spring (CS) than to that of T. monococcum. The pattern in Ae. tauschii was similar to that of the D genome of CS. Only partial resemblance was found between the RFLP patterns of the species with the S genome and the B genome of CS. Received: 10 February 2000 / Accepted: 21 February 2000     

Chromosome substitutions of Triticum timopheevii in common wheat and some observations on the evolution of polyploid wheat species

Whether the two tetraploid wheat species, the well known Triticum turgidum L. (macaroni wheat, AABB genomes) and the obscure T. timopheevii Zhuk. (A^tA^tGG), have monophyletic or diphyletic origin from the same or different diploid species presents an interesting evolutionary problem. Moreover, T. timopheevii and its wild form T. araraticum are an important genetic resource for macaroni and bread-wheat improvement. To study these objectives, the substitution and genetic compensation abilities of individual T. timopheevii chromosomes for missing chromosomes of T. aestivum Chinese Spring (AABBDD) were analyzed. Chinese Spring aneuploids (nullisomic-tetrasomics) were crossed with a T. timopheevii x Aegilops tauschii amphiploid to isolate T. timopheevii chromosomes in a monosomic condition. The F₁ hybrids were backcrossed one to four times to Chinese Spring aneuploids without selection for the T. timopheevii chromosome of interest. While spontaneous substitutions involving all A^t- and G-genome chromosomes were identified, the targeted T. timopheevii chromosome was not always recovered. Lines with spontaneous substitutions from T. timopheevii were chosen for further backcrossing. Six T. timopheevii chromosome substitutions were isolated: 6A^t (6A), 2G (2B), 3G (3B), 4G (4B), 5G (5B) and 6G (6B). The substitution lines had normal morphology and fertility. The 6A^t of T. timopheevii was involved in a translocation with chromosome 1G, resulting in the transfer of the group-1 gliadin locus to 6A^t. Chromosome 2G substituted for 2B at a frequency higher than expected and may carry putative homoeoalleles of gametocidal genes present on group-2 chromosomes of several alien species. Our data indicate a common origin for tetraploid wheat species, but from separate hybridization events because of the presence of a different spectrum of intergenomic translocations.     

Patterns of trait variation in the diploid wheats (Triticum,Aegilops) and the tetraploid speciesTriticum diccocoides

Eighteen earliness and morphological traits were examined in from 2 to 14 lines each of 10 diploid members of the wheat complex,Triticum-Aegilops, and 15 lines of the tetraploid speciesTriticum diccocoides. In general, earliness traits have the greatest relative between line vs. within line variation of all the traits examined. Within species, earliness traits are the principle set of characters around which evolve between line trait differences, one of the most important oich is leaf dimensions. At the genus level, earliness traits are independent of leaf dimensions and plant height characters. Thus, the pattern of evolution at the genus level is different from that exhibited in each of the species. Biological and evolutionary implications of these findings are discussed.     

Recurrent deletions of puroindoline genes at the grain hardness locus in four independent lineages of polyploid wheat

Polyploidy is known to induce numerous genetic and epigenetic changes but little is known about their physiological bases. In wheat, grain texture is mainly determined by the Hardness (Ha) locus consisting of genes Puroindoline a (Pina) and b (Pinb). These genes are conserved in diploid progenitors but were deleted from the A and B genomes of tetraploid Triticum turgidum (AB). We now report the recurrent deletions of Pina-Pinb in other lineages of polyploid wheat. We analyzed the Ha haplotype structure in 90 diploid and 300 polyploid accessions of Triticum and Aegilops spp. Pin genes were conserved in all diploid species and deletion haplotypes were detected in all polyploid Triticum and most of the polyploid Aegilops spp. Two Pina-Pinb deletion haplotypes were found in hexaploid wheat (Triticum aestivum; ABD). Pina and Pinb were eliminated from the G genome, but maintained in the A genome of tetraploid Triticum timopheevii (AG). Subsequently, Pina and Pinb were deleted from the A genome but retained in the A(m) genome of hexaploid Triticum zhukovskyi (A(m)AG). Comparison of deletion breakpoints demonstrated that the Pina-Pinb deletion occurred independently and recurrently in the four polyploid wheat species. The implications of Pina-Pinb deletions for polyploid-driven evolution of gene and genome and its possible physiological significance are discussed.     

Salt‐tolerance diversity in diploid and polyploid cotton (Gossypium) species

The development of salt‐tolerant genotypes is pivotal for the effective utilization of salinized land and to increase global crop productivity. Several cotton species comprise the most important source of textile fibers globally, and these are increasingly grown on marginal or increasingly saline agroecosystems. The allopolyploid cotton species also provide a model system for polyploid research, of relevance here because polyploidy was suggested to be associated with increased adaptation to stress. To evaluate the genetic variation of salt tolerance among cotton species, 17 diverse accessions of allopolyploid (AD‐genome) and diploid (A‐ and D‐genome) Gossypium were evaluated for a total of 29 morphological and physiological traits associated with salt tolerance. For most morphological and physiological traits, cotton accessions showed highly variable responses to 2 weeks of exposure to moderate (50 mm NaCl) and high (100 mm NaCl) hydroponic salinity treatments. Our results showed that the most salt‐tolerant species were the allopolyploid Gossypium mustelinum from north‐east Brazil, the D‐genome diploid Gossypium klotzschianum from the Galapagos Islands, followed by the A‐genome diploids of Africa and Asia. Generally, A‐genome accessions outperformed D‐genome cottons under salinity conditions. Allopolyploid accessions from either diploid genomic group did not show significant differences in salt tolerance, but they were more similar to one of the two progenitor lineages. Our findings demonstrate that allopolyploidy in itself need not be associated with increased salinity stress tolerance and provide information for using the secondary Gossypium gene pool to breed for improved salt tolerance.     

Inheritance of dense spike in diploid wheat and Aegilops squarrosa

The individuals of diploid wheat Triticum boeoticum, T. monococcum and T. sinskajae and goatgrass Aegilops squarrosa were picked out with screening the dense spike characteristics. The dense-spike accessions were discovered in diploid wheat (T. sinskajae) and Ae. squarrosa. Inheritance of the dense spike was studied. The trait was found to be controlled by a recessive gene in T. sinskajae and by an incomplete dominant gene in Ae. squarrosa. The dosage effect of dominant gene C was detected in interspecific pentaploid F1 hybrid plants T. compactum x T. palmovae (2n =35, A(u)A(b)BDD genome). The spike of pentaploid hybrid was not so dense as compared to hexaploid wheat T. compactum. This is the first report showing similarity of the expression of dominant gene C on D genome of the hexaploid wheat to that of dense spike gene in Ae. squarrosa. The existence of dense-spike accessions of Ae. squarrosa allows us to hypothesize that the origin of T. compactum is independent from that of common wheat.     

Species relationships and genetic variation in the diploid wheats (Triticum,Aegilops) as revealed by starch gel electrophoresis

Twenty enzyme loci were examined in the diploid species ofTriticum andAegilops for allelic variation by starch gel electrophoresis. SectionSitopsis, including the five species,Ae. speltoides, Ae. lingissima, Ae. sharonensis, Ae. bicornis andAe. searsii form a close subgroup withAe. speltoides slightly removed from the others.T. monococcum s. lat., was found to be closest to the species of theSitopsis group.Ae. comosa, Ae. umbellulata andAe. uniaristata form a second subgroup withAe. caudata most closely related to these species.Ae. squarrosa appears almost equally related to all of the species, showing no special affinity for any one species group. Nineteen out of twenty loci examined were polymorphic with a mean of 6.7 alleles per locus. Species could be, for most loci, characterized by the presence of predominant alleles. A conspicious genetic characteristic ofTriticum-Aegilops is the sharing of these predominant alleles between species. Within species variation is characterized by a diffuse distribution of secondary alleles.     

A fertile amphiploid between diploid wheat (Triticum tauschii) and crested wheat grass (Agropyron cristatum).

Alloploidy, one of the most efficient evolutionary mechanisms in nature, has not been extensively exploited in plant breeding programmes. Many genomic combinations remain to be created by plant breeders, to be used directly as new crops or indirectly to widen the genetic basis of crops. The Triticeae tribe, to which wheat belongs, is among the botanical groups in which this strategy has been successfully explored. However, there remain valuable genomic combinations that have not been obtained at the diploid level. The Agropyron complex (wheat-grasses) has recently been the focus of attention for interspecific hybridization, but intergeneric hybrids or amphiploids with wheat have not been reported at the diploid level. Here we report synthesis of a tetraploid amphiploid between Triticum tauschii and Agropyron cristatum by crossing two tetraploid accessions. Using total genome in situ hybridization (GISH) staining on metaphase I pollen mother cells, data on allosyndetic and autosyndetic chromosome pairing have been obtained. These data support the view that the A. cristatum tetraploid parent used in the synthesis of the amphiploid has a segmental alloploidy nature.     

Chloroplast DNA variation in diploid and polyploid species of Bromus (Poaceae) subgenera Festucaria and Ceratochloa

Summary Chloroplast DNA (cpDNA) restriction endonuclease patterns are used to examine phylogenetic relationships between Bromus subgenera Festucaria and Ceratochloa. Festucaria is considered monophyletic based on the L genome, while Ceratochloa encompasses two species complexes: the B. catharticus complex, which evolved by combining three different genomes, and the B. carinatus complex, which is thought to have originated from hybridization between polyploid species of B. catharticus and diploid members of Festucaria. All species of subgenus Ceratochloa (hexaploids and octoploids) were identical in chloroplast DNA sequences. Similarly, polyploid species of subgenus Festucaria, except for B. auleticus, were identical in cpDNA sequences. In contrast, diploid species of subgenus Festucaria showed various degrees of nucleotide sequence divergence. Species of subgenus Ceratochloa appeared monophyletic and phylogenetically closely related to the diploid B. anomalus and B. auleticus of subgenus Festucaria. The remaining diploid and polyploid species of subgenus Festucaria appeared in a distinct grouping. The study suggests that the B. catharticus complex must have been the maternal parent in the proposed hybrid origin of B. carinatus complex. Although there is no direct evidence for the paternal parent of the latter complex, the cpDNA study shows the complex to be phylogenetically very related to the diploid B. anomalus of subgenus Festucaria.     

Characterization of low-molecular-weight glutenin subunit genes of Aegilops section Sitopsis and comparative analysis with those of wheat (Triticum aestivum L.) and some Aegilops species

Journal of Genetics -     

A chromosome-specific sequence common to the B genome of polyploid wheat and Aegilops searsii

A low-copy, non-coding chromosome-specific DNA sequence, isolated from common wheat, was physically mapped to the distal 19% region of the long arm of chromosome 3B (3BL) of common wheat. This sequence, designated WPG118, was then characterized by Southern hybridization, PCR amplification and sequence comparison using a large collection of polyploid wheats and diploid Triticum and Aegilops species. The data show that the sequence exists in all polyploid wheats containing the B genome and absent from those containing the G genome. At the diploid level, it exists only in Ae. searsii, a diploid species of section Sitopsis, and not in other diploids including Ae. speltoides, the closest extant relative to the donor of the B genome of polyploid wheat. This finding may support the hypothesis that the B-genome of polyploid wheat is of a polyphyletic origin, i.e. it is a recombined genome derived from two or more diploid Aegilops species.     

Transferability of wheat microsatellites to diploid Aegilops species and determination of chromosomal localizations of microsatellites in the S genome.

Overall, 253 genomic wheat (Triticum aestivum) microsatellite markers were studied for their transferability to the diploid species Aegilops speltoides, Aegilops longissima, and Aegilops searsii, representing the S genome. In total, 88% of all the analyzed primer pairs of markers derived from the B genome of hexaploid wheat amplified DNA fragments in the genomes of the studied species. The transferability of simple sequence repeat (SSR) markers of the T. aestivum A and D genomes totaled 74%. Triticum aestivum-Ae. speltoides, T. aestivum-Ae. longissima, and T. aestivum-Ae. searsii chromosome addition lines allowed us to determine the chromosomal localizations of 103 microsatellite markers in the Aegilops genomes. The majority of them were localized to homoeologous chromosomes in the genome of Aegilops. Several instances of nonhomoeologous localization of T. aestivum SSR markers in the Aegilops genome were considered to be either amplification of other loci or putative translocations. The results of microsatellite analysis were used to study phylogenetic relationships among the 3 species of the Sitopsis section (Ae. speltoides, Ae. longissima, and Ae. searsii) and T. aestivum. The dendrogram obtained generally reflects the current views on phylogenetic relationships among these species.     

Trace elements distribution and species fractionation in the wheat (Triticum aestivum) plant

Abstract

The status of 13 trace elements’ (both essential and toxic) was investigated in individual parts of the winter wheat plant(Triticum aestivum) taken during its whole cultivation period. The study includes the determination of total concentrations, portions soluble in 0.02 mol L^?1 Tris-HCI buffer solution (pH = 7.5), and the fractionation of soluble species of elements by SEC and ICP/MS. Ligands of trace elements from a low-molecular weight SEC fraction were isolated by affinity chromatography and characterised by MALDI/MS analyses and by amino acids composition. Inhomogeneous accumulation of trace elements was found in the analysed plant tissues. The concentrations of elements are also affected by the maturity of the plants. The distribution of the soluble species of the elements between chromatographic fractions exhibited some regularity in all the samples. Substantial amounts of trace elements are located in a low-molecular weight fraction (< 2 kDa). Only chromatograms of Zn (grain) and Cu (all samples) contain significant medium-molecular and high-molecular weight fractions. Compounds isolated from the low-molecular weight fractions are rich in cystein and dicarboxylic amino acids or their amides. MALDI/MS spectra of these compounds isolated from shoots, straw and grain confirmed the presence of the phytochelatin PC₅.     

Genetic control of aspartate aminotransferase isoenzymes in Aegilops and Triticum species

Zymograms of the aspartate aminotransferase (AAT, EC 2.6.1.1) activity in leaf extracts from Aegilops and Triticum species revealed three AAT zones, denoted according to the decreasing electrophoretic mobility towards the anode as AAT-1, AAT-2 and AAT-3. The AAT activity zymograms of subcellular fractions isolated from T. aestivum seedlings made it possible to establish that the AAT-1 zone is located in the mitochondria, AAT-2 in the chloroplasts and AAT-3 in the cytoplasm. Most of the total AAT activity from wheat leaves arises from the chloroplasts and cytoplasm. The AAT-3 zone exhibited the lowest electrophoretic mobility, but 3 isoenzymes occurring within were the most visibly separated. The occurrence of a single band in this zone at the AAT-3a position (closest to the anode) for the aneuploid CS3ASDt AABBDD line (the absence of long arms of the 3rd pair of homologous chromosomes in the A genome) and at the AAT-3c position for Ae. umbellulata (genome UU), as well as three bands in the whole zone for T. durum (AABB) and T. aestivum (AABBDD) each, made it possible to evaluate the subunit composition of isoenzymes in the AAT-3 zone. The band at the AAT-3a position in the zymogram is formed from bb dimers, AAT-3b from ab and AAT-3c from aa. By comparing the distribution of isoenzyme bands intensities (the result of enzymatic activity) with the mathematical models, the frequencies of the occurrence of the a and b subunits within AAT-3 zone were evaluated. In AAT-3 from T. durum, a and b occurred at the ratio of 0.54:0.46, and in that from T. aestivum - 0.62:0.38, respectively.     

Distribution of basic diploid and polyploid species of Isoetes in East Asia

Aims Isoetes L. is an ancient, primitive genus of heterosporous lycopsids characterized by a strongly reduced plant. The genus occupies a unique position in plant evolution as the closest relatives of the famous tree lycopods. Hybridization and allopolyploid speciation as well as habitat preference are regarded as having played an important role in the evolution of the genus Isoetes. However, it is still uncertain what factors have impacted upon hybridization and allopolyploid speciation of the genus Isoetes. Our understanding of the origin, evolution and modern distribution pattern of Isoetes in East Asia would benefit from investigations into the relationship between the unique geographical location and topographic features and the existing fossil record in the region. Methods The chromosome number was determined from known 81 populations of 10 species of Isoetes in East Asia. The altitude was obtained in location of every population. T‐test was used to evaluate the altitude difference between diploid and polyploid populations. Data of Japanese Isoetes from Takamiya et al. was used in the study. Results There are 10 known species of Isoetes with four diploids and six polyploids in East Asia. The four diploid species (2n = 22) are found at high altitudes (mean altitude = 2649.67 ± 1396.16 m, n = 18) and isolated from each other. In contrast, the six polyploid species widely occur in low altitude regions (mean altitude = 182.62 ± 181.44 m, n = 63) and are partially sympatric. Highly significant differences (P < 0.001) were observed between the mean altitude of locations of populations of diploids and polyploids. Main conclusions The polyploidy speciations of Isoetes in East Asia might originate and develop from Holocene (Quaternary). The present pattern of distribution of Isoetes in East Asia is the result of allopatric speciation derived from vicariance, dispersal and combinations of both, and significantly correlative with the geological history and geographical changes. The change of altitude might have played an important role in allopolyploid speciation and the pattern of distribution of the genus Isoetes in East Asia by exerting a considerable influence on dispersal and hybridization opportunities of Isoetes species.