This paper reviews our results on plasmon analysis of the Triticum-Aegilops complex after presenting the background and pioneering work. 1) Genetic effects of 47 plasmons of Triticum-Aegilops accessions on 21 wheat characters were analyzed using 12 euplasmic and 551 alloplasmic lines, in which 12 common wheat genotypes and 47 plasmons were combined in all possible combinations, except for one lethal combination. Characteristics of the individual plasmons on wheat phenotypes were clarified, based on which they were classified into 15 types. 2) Plastome and chondriome diversities were studied by RFLP analyses of chloroplast (ct) and mitochondrial (mt) DNAs, respectively. Based on the data obtained, numbers of differential mutations in the plastomes and genetic distances for the chondriomes were estimated for all pairs of the plasmons, based on which their phylogenetic trees were constructed. 3) Combining the results of the above works, 47 plasmons were classified into 18 types plus five subtypes, to which plasmon symbols were assigned. 4) Differentiation of the plasmon at the diploid level and maternal lineages of the polyploid species became elucidated. 5) Referring to the genome symbols designated by previous workers, the genome-plasmon constitutions of all Triticum-Aegilops species were clarified, based on which species relationships of this complex became established, the first example of the generic level throughout the plant and animal kingdoms. 6) Origins of some polyploid species were shown to be more recent than some other relatives, three examples being Timopheevi vs. Emmer group of tetraploid wheat, Ae. triaristata vs. Ae. ovata of the Polyeides section and Ae. ventricosa vs. Ae. crassa of the Vertebrata section of Aegilops, the former being of more recent origin than the latter in each pair. 7) Possible sites of plasmagene mutations responsible for three plasmon-controlled traits were located on the plastome or chondriome phylogenetic tree. And finally, 8) some unsolved plasmon-related problems were pointed out.
During the last decade several phylogenetic studies of Hordeum were published using a multitude of loci from the chloroplast and nuclear genomes. In many studies taxon sampling was not representative and, thus, does not allow the inference of relationships among species. Generally, chloroplast data seem not suitable for reliable phylogenetic results, as far reaching incomplete lineage sorting result in nearly arbitrary species relationships within narrow species groups, depending on the individuals included in the analyses. Nuclear loci initially resulted at contradictory phylogenetic hypotheses. However, combining at least three nuclear loci in total evidence analyses finally provides consistent relationships among Hordeum species groups, and supports data from earlier cytological and karyological studies. Thus, recently published phylogenies agree on the monophyly of the four Hordeum genome groups (H, I, Xa, Xu), monophyly of the H/Xu and I/Xa groups, and separation between Asian and American members within the I-genome group. A new infrageneric classification of Hordeum is proposed, dividing the genus in subgenus Hordeum comprising sections Hordeum and Trichostachys, and subgenus Hordeastrum with sections Marina, Nodosa, and Stenostachys. The latter consists of two series reflecting the geographical distribution of the taxa, i.e. series Sibirica with Central Asian taxa and series Critesion comprising native taxa from the Americas. In section Nodosa all allopolyploid taxa are grouped, which are characterized by I/Xa genome combinations.
Barley is one of the major cereals in the world. The analysis of genomes is important in modern breeding, but the barley genome is too huge and complicated that it is still difficult to arrange sequenced pieces of the genome in order. Each of the barley chromosomes or chromosome arms has been added to common wheat and such barley chromosome addition lines have been used in determining the chromosomal regions of genes and DNA markers. It is undoubtedly desirable to have the genome divided into smaller pieces in separate common wheat lines. There is a unique genetic system in common wheat that induces frequent chromosomal structural rearrangements. This system is called the gametocidal (Gc) system involving alien chromosomes called Gc chromosomes, which were introduced into common wheat from certain wild species belonging to the genus Aegilops. When the Gc chromosome exists in a common wheat plant in monosomic condition, the plant produces two types of gamete, one with the Gc chromosome and the other without the Gc chromosome; chromosomal rearrangements occur only in the latter one. Such Gc-induced chromosomal rearrangements are either lethal to gametes or semi-lethal, and in the latter case the gametes are fertilized to develop into viable zygotes carrying rearranged chromosomes. The Gc system proved to be effective in inducing structural rearrangements in barley chromosomes added to common wheat, as well as in common wheat chromosomes. Thus-induced rearranged chromosomes include deletions of barley chromosomes and translocations between the barley and wheat chromosomes. The present author termed common wheat lines carrying rearranged barley chromosomes ‘dissection lines’ of a barley chromosome. So far dissection lines for three barley chromosomes have been produced and used in the cytological mapping of the barley chromosomes. In this article the progress in the cytological dissection of the barley genome is described.
It is well known that Elymus arose through hybridization between representatives of different genera and several different polyhaplomic genomes have been described. Cytogenetically, five basic genomes (St, H, Y, P and W) in different combinations have been found in the genus. The vast majority of species are tetraploids and they are characterized by having the StY genome or the StH genome. It is not known where the Y genome originated, although it is a common in Elymus from Central and East Asia. It has been hypothesized from isozymic and cytological studies of Elymus species that the Old and New World taxa may be of separate origin of the H genome in the StH genome species. Data from single copy of nuclear gene RPB2 indicated that the Eurasian and American StH genome species have independent alloploid origins with different H-genome donors. This hypothesis is needed to be tested by using more molecular data. Sequences from single copy of nuclear genes (RPB2, β-amylase gene and EF-G) indicated that StY genome species is allopolyploid origin. This paper presents a briefly review on current status of molecular evolution and origin of tetraploid Elymus species.
The effective use of wheat biodiversity in breeding programs is dependent on a sound conservation strategy for sources of biodiversity, and on appropriate techniques of incorporation into modern cultivars. Producing artificial wheat amphiploids using genomes of related species is an effective way to increase the available gene pool. However, artificial amphiploids should be given botanic names and positions within genus Triticum classification to ensure effective collection and preservation in gene banks. In this review, an attempt to integrate the results of molecular-genetic analyses of natural and artificial wheats with their taxonomy has been made. The correspondence of earlier evolutionary and taxonomic specifications to phylogenetic relationships within Triticum has been estimated using chloroplast and nuclear DNA sequence data. The results indicated close relationships between all artificial and natural species. Based on the data, all wild and cultivated diploid wheat species were united in a separate section, Monococcon. Different variants of nuclear Acc-1, Pgk-1, and Vrn-1 genes have been detected in diploid A genome species. Detailed analysis of the genes showed that one of these variants was a progenitor for all A genomes of polyploid wheats except for that in Triticum zhukovskyi and some of the artificial amphiploids.
The tribe Triticeae includes some of the world’s most important cereal crops, such as wheat, barley, and rye. It also includes important, mostly perennial, fodder grasses such as Agropyron, Elymus, Leymus, Psathyrostachys, and others. Many wild annual grasses of the tribe Triticeae belong to a highly valuable gene pool for cereal breeding—Triticum, Aegilops, Secale, Hordeum, Dasypyrum, etc., and some are interesting ephemeral plants of deserts, including Eremopyrum, Crithopsis, and Heteranthelium. Another group is interesting taxonomically, because they are on the border or just beyond the limit of the tribe, such as Brachypodium and Henrardia. Triticeae is a taxonomically controversial group at both the species and generic level. One extreme is considering Triticum to be the only genus of Triticeae, and an opposite extreme is accepting of a huge amount of often monotypic genera. Therefore, it seemed appropriate to review here several issues of the taxonomy and phylogeny of the tribe Triticeae.
Solid deposits of amorphous hydrated silica are formed at specific intracellular and extracellular locations in many plant taxa, including all taxa in Triticeae. These deposits of silica are called phytoliths, literally meaning “plant-rocks.” Many plants produce phytoliths with morphological characteristics that appear unique to a given taxon, a phenomenon giving them taxonomic significance. When plant tissue decomposes, any phytoliths formed are released into the surrounding environment thus becoming microfossils of the plants that produced them. Analysis of microfossil phytoliths can provide information to researchers in a wide variety of disciplines, including, archaeobotany, paleoecology, phytogeography and systematics. This paper reviews current methodologies and results of typologic and morphometric analysis of wheat and barley phytoliths.
The tribe Triticeae is a taxon in the Poaceae that includes several important cereal crops and forage grasses. All its species, including those that are not used for cereals or forage, are potential sources of genes for crop and forage improvement so they all have high economic value. Taxonomic treatments, including those of the Triticeae, are the basis for identification. They are often designed to reflect phylogenetic relationships and provide a guide for germplasm utilization. Traditional taxonomic treatments of the Triticeae were based on comparative morphology and geography. Morphological characters are phenotypes of an organism, resulting from interactions between or among dominant genes and environmental factors. Morphology cannot reflect recessive inheritance. Similar environmental conditions may result in morphological convergence in distantly related taxa and different environmental conditions in morphological divergence of closely related taxa. Consequently, traditional morphological taxonomy may result in misclassification. Cytogenetic and/or molecular genomic analysis may reveal such mistakes. On the basis of recent genomic investigations of the Triticeae, we have recognized 30 genera in this tribe. The taxonomic changes and genomic constitution of these genera are presented in this paper.
The seed storage proteins (SSPs) of cultivated wheat (Triticum aestivum and T. durum), namely, glutenin and gliadin, impart viscoelastic properties to bread dough, making wheat well suited for bread-making. Extensive studies on wheat SSPs have been carried out and revealed genetic diversity among wheat cultivars. Here, we review the studies of SSPs from more exotic species in the Triticeae tribe, primarily based on our own recent studies. SSPs of barley (Hordeum vulgare), homologous to those in wheat, exhibit quite different properties to wheat SSPs and do not produce viscoelastic dough. However, SSPs of a wild barley species (H. chilense) possess similar characteristics to the proteins of wheat. SSPs of rye (Secale cereale) substituted for wheat SSPs result in inferior quality. SSPs of Aegilops searsii and Ae. longissima have positive effects on quality, while Ae. umbellulata and Ae. geniculata (Ug genome) SSPs have a negative effect on bread-making quality. SSPs located on chromosome 1Mg of Ae. geniculata and a chromosome 1E of Thinopyrum elongatum have positive effects in addition lines but not in substitution lines for chromosome 1D of wheat. In contrast, SSPs of Th. intermedium have positive effects, even in cases of substitution for chromosome 1D of wheat, indicating promising potential for improvement of bread-making quality of wheat. Based on these results, we discuss the possibilities for utilizing the genetic variation of exotic Triticeae species for breeding improved quality traits in wheat.
The natural ability of plants to release chemical substances from their roots that have a suppressing effect on nitrifier activity and soil nitrification, is termed ‘biological nitrification inhibition’ (BNI). Though nitrification is one of the critical processes in the nitrogen cycle, unrestricted and rapid nitrification in agricultural systems can result in major losses of nitrogen from the plant-soil system. This nitrogen loss is due to the leaching of nitrate out of the rooting zone and emission of gaseous oxides of nitrogen to the atmosphere, where it causes serious pollution problems. Using a newly developed assay system that quantifies the inhibitory activity of plant roots (i.e. BNI capacity), it has been shown that BNI capacity is widespread among crops and pastures. A tropical pasture grass, Brachiaria humidicola has been used as a model system to characterize BNI function, where it was shown that BNIs can provide sufficient inhibitory activity to suppress soil nitrification and nitrous oxide emissions. Given the wide-range of genetic diversity found among the Triticeae, and the current availability of genetic tools for moving traits/genes across members, there is great potential for introducing/improving the BNI capacity of economically important members of the Triticeae (i.e. wheat, barley and rye). This review outlines the current status of knowledge regarding the potential for genetic improvement in the BNI capacity of the Triticeae. Such approaches are critical to the development of the next-generation of crops and production systems where nitrification is biologically suppressed/regulated to reduce nitrogen leakage and protect the environment from nitrogen pollution
Flowering is a very important event in plant propagation. Plants other than absolute response plants can produce flowers under any conditions. Recent studies using model plants have provided important information on flowering mechanisms. Under floral inductive conditions, the long-day (LD) plant Arabidopsis and the short-day (SD) plant rice use the same gene set, CO and FT (Hd1 and Hd3a in rice), which functions as an important promoter for flowering. In rice, Hd1 represses Hd3a expression under non-inductive conditions but not under inductive conditions. The regulation of Hd3a by Hd1 is reversed under two conditions in rice. This system is not found in Arabidopsis. Barley (Hordeum vulgare) is more closely related to rice than to Arabidopsis, but barley is a LD plant like Arabidopsis. Although barley has orthologs to CO and FT, HvCO1 and HvFT1, and their expression and functions under inductive conditions have been analyzed, the pathway under non-floral-inductive conditions remains unclear. We recently reported on genes that promote flowering under SD conditions in barley. In this review, we focus on the mechanisms of photoperiodic flowering in barley, especially the promoting pathway under non-inductive conditions. Flowering mechanisms specific to barley are also presented in comparison with the mechanisms of Arabidopsis and rice.
The Triticeae crops comprise wheat, barley, rye and triticale, which together provide a major portion of the world’s food and feed. The growing demand for human nutrition and renewable energy requires an intensification in application-oriented research and the establishment and utilization of current biotechnology in these crops. Genetic transformation provides an important means both to elucidate gene function, and to engineer crop plants in a directed and precise way. This review covers a range of issues surrounding the production of stable transgenic lines within the Triticeae. Some quality aspects of transgenesis of particular relevance to the Triticeae are also discussed.
Our goal was to determine whether the genomic groups of perennial species Triticeae having solitary spikelets could be identified morphologically and, if so, to construct identification keys that could be used for this purpose. If so, it would strengthen the argument for recognizing such groups as genera. We conducted Discriminant and Random Forest® analyses of 61 characters scored on 218 herbarium specimens representing 13 genomic groups. In addition, we closely examined some additional characters that came to our attention, evaluating our findings on specimens not scored for the two kinds of analysis. Random Forest® analysis was almost always more successful in distinguishing the genomic groups, whether separating all 13 groups or a subset of the 13. The results suggest that it is usually possible to identify the genomic group to which a specimen of perennial Triticeae with solitary spikelets belongs on the basis of its morphology but that doing so will require examination of characters that have not been considered particularly important in the past. Among these are the length of the middle inflorescence internodes, the width of the palea tip, and the morphology of the glumes. Generic descriptions and keys have been posted to the web (see http://herbarium.usu.edu/triticeae). They include all the genera that we recognize in the tribe, not just those included in the analyses, and will be improved as additional information becomes available.
Domesticated timopheevi wheat (Triticum timopheevi) is an endemic crop of western Georgia in Transcaucasia. It has a distinct nuclear genome (2n = 28, AAGG) and is genetically isolated from other wheat species. To clarify the genetic diversity and the domestication of this interesting wheat, we analyzed molecular variation at 23 microsatellite loci in the chloroplast genome. Allelic diversity was evaluated using 94 accessions representing domesticated timopheevi wheat (T. timopheevi), wild timopheevi wheat (T. araraticum), and wild emmer wheat (T. dicoccoides). The average diversity index (H) in T. araraticum (0.206) was smaller than that in T. dicoccoides (0.284). No polymorphisms were detected among the six accessions of T. timopheevi, suggested a monophyletic origin of domesticated timopheevi wheat. Phylogenetic analyses of the plastotypes revealed clear differences between the chloroplast DNA of timopheevi wheat and emmer wheat, and thus supported the hypothesis that these two wheat species originated independently. None of the T. araraticum plastotypes collected in Transcaucasia were closely related to the T. timopheevi plastotype. On the other hand, the plastotypes found in northern Syria and southern Turkey showed closer relationships with T. timopheevi. These results suggested that the domestication of timopheevi wheat might have occurred in the region including southern Turkey and northern Syria.
Aegilops tauschii Coss. (syn Ae. squarrosa L.) is a wild diploid wheat species. It has a wide natural species range in central Eurasia, spreading from northern Syria and Turkey to western China. Ae. tauschii is known as the D genome progenitor of hexaploid bread wheat. The genealogical and geographical structure of variation of morphological traits was analyzed using a diverse array of 205 sample accessions that represented the entire species range. In total, 27 traits, including anther and pistil shape and internode length, were examined in this study. Large-scale natural variation was found for all examined traits. Geographically, significant longitudinal clines were detected for anther size, internode length and spike size and shape. Anthers tended to be small in accessions from the eastern region. Internodes also tended to be short, whereas spikes tended to be long in accessions from the eastern region. Spikelet density per spike tended to be high in the eastern habitats. In the process of west-to-east dispersal, Ae. tauschii underwent extensive morphological, genetic and ecological diversification that produced the variation seen among today’s natural populations.
We previously showed that H. secalinum and H. capense are allotetraploids carrying the Xa genome of H. marinum and the I genome of an unidentified diploid species. In this study, intraspecific variation in each tetraploid species was investigated with regard to intergenomic translocations and chromosomal distribution of rDNA sites. Genomic in situ hybridization revealed that three H. secalinum accessions examined did not carry intergenomic translocations, but that two of three H. capsense accessions analyzed carried a pair of intergenomic translocations. Multicolour fluorescence in situ hybridization showed that H. secalinum included two types of rDNA pattern differing in the presence or absence of an extra 5S rDNA site in a submetacentric chromosome pair of the Xa-genome origin. The extra 5S rDNA site was found in all H. capense accessions examined. This 5S rDNA site is characteristic of H. marinum ssp. gussoneanum, but is absent in ssp. marinum. Polymorphisms in the 5S rDNA site infer that H. secalinum included two types, one having ssp. gussoneanum 2x and the other having ssp. marinum, as the Xa-genome donor. We conclude that H. capense originated from a limited number of H. secalinum accessions introduced probably through migrating birds to South Africa.
Phylogenetic relationships within the genus Hordeum were investigated based on nucleotide sequences of the thioredoxin-like (HTL) gene. We analyzed amplified genomic DNA fragments of the HTL gene from 11 Hordeum species including 16 taxa (25 accessions), which cover mainly diploid accessions together with several tetraploid accessions. Phylogenetic analysis based on the HTL sequences demonstrated a clear divergence of the four basic genomes I (H. vulgare and H. bulbosum), Xa (H. marinum), Xu (H. murinum) and H (other species) in the genus. Phylogenetic clustering also led us to infer two separate clades, one containing the I and Xu, and the other containing the Xa and H genomes. In the diploid H-genome species, American species were confirmed to be closely related and divergent from Asian species. Analysis of the Xa-genome group suggested an alloploid origin of tetraploid H. marinum ssp. gussoneanum by hybridization between the diploid cytotypes of ssp. marinum and ssp. gussoneanum. Our data also supported the hypothesis that two tetraploid cytotypes of H. murinum (ssp. murinum and ssp. leporinum) have an alloploid origin, where one genome was presumably derived from the diploid cytotype ssp. glaucum and the other from an unknown Xu-genome species.
The section Sitopsis in the genus Aegilops includes five species, Ae. speltoides, Ae. longissima, Ae. sharonensis, Ae. searsii, and Ae. bicornis, which share the SS genome. Although extensive molecular studies have indicated Ae. speltoides as a donor of BB or GG genome to polyploid wheat species, the precise relationships among SS, BB, and GG genomes remain unclear. PolA1 is a single-copy nuclear gene encoding the largest subunit of RNA polymerase I. Highly polymorphic PolA1 exon 20 sequences were analyzed for 11 Triticum–Aegilops, 13 Hordeum and three related species. Phylogenetic analyses of the PolA1 gene showed that Triticum–Aegilops and Hordeum species were distinctly separated into two clades. Two related species, Secale cereale and Dasypyrum villosum, were grouped into Triticum and Hordeum clades, respectively. Interestingly, seven accessions of the Sitopsis species were clustered into the Hordeum clade whereas two accessions belonged to the Triticum clade. In contrast, all accessions of Sitopsis species shared the same haplotype of plastid PSID sequences with Triticum–Aegilops species. This inconsistency in phylogeny between nuclear and cytoplasmic sequences suggested that the Sitopsis species probably originated through introgressive hybridization between ancestral species of Triticum–Aegilops and Hordeum.
A hexaploid form of Hordeum brachyantherum ssp. brachyantherum was discovered in California in 1980, and its origin has since been studied over the past three decades. We applied EF-G, a nuclear DNA sequence, to infer the parents of the hexaploid form. In polyploid taxa, amplified DNAs were cloned into a vector, and EF-G copies were amplified from the colonies by PCR and digested with restriction enzymes to separate different types. Phylogenetic analysis was performed based on the DNA sequences. The result showed that H. brachyantherum ssp. brachyantherum 6x and 4x carried one identical DNA sequence of 910 bp, and had closely related DNA sequences of 931 bp. H. brachyantherum ssp. brachyantherum 6x and H. marinum ssp. gussoneanum 2x shared one identical DNA sequence of 915 bp. From these results we hypothesized that H. brachyantherum ssp. brachyantherum 6x has evolved by an outcrossing between H. marinum ssp. gussoneanum 2x and H. brachyantherum ssp. brachyantherum 4x, followed by a chromosome doubling. Our results also indicate that H. marinum was involved in the polyploidization of H. secalinum, H. capense, and H. marinum. The origins of H. jubatum and H. depressum are discussed.
The number of spikelets per rachis node is a key taxonomic character in the tribe Triticeae. In intergeneric F1 plants, including wheat (Triticum) and barley (Hordeum), the single spikelet trait was epistatic, whereas it showed intermediate response in the interspecific hybrids involving the genus Elymus. Further genetic analysis has been hindered by the high sterility of the F1 hybrid plants. In the F1E. tsukushiensis × H. vulgare, occasional variation in the number of spikelets was seen, apparently due to somatic chromosome instability. This indicates that these aneuploids should provide useful material for further analysis. A series of nullisomics and nulli-tetra compensation lines of Triticum aestivum ssp. vulgare cv. Chinese Spring was observed. From a consideration of all these results, it is proposed that a dosage of six genes on the homoeologous chromosomes of group-2 may suppress the formation of paired spikelets at the rachis nodes at the hexaploid level of wheat.
Domesticated barleys produce either two- or six- rowed spikes, whereas their immediate wild ancestor, wild barley, is monomorphic for the two-rowed type. The six-rowed spike is a recessive character, conditioned by a major gene at the vrs1 locus. The wild-type (two-rowed) gene includes a homeodomain-leucine zipper I (HD-Zip I) sequence (HvHox1). The correspondence between peptide sequence and some spike variants was studied by re-sequencing the HvHox1 sequence across a large sample of both wild and domesticated accessions.
Revolver is a multi-gene family dispersed through Triticeae genomes like transposons. Revolver is similar to class II transposable elements and shows considerable quantitative variation in wheat and its relatives. The highest copy number of Revolver is found in Secale cereale (RR) and the lowest in hexaploid wheat Triticum aestivum (AABBDD). In this study, Revolver copy numbers were determined in synthetic hexaploid wheat lines from crosses between Aegilops tauschii (DD) and T. turgidum tetraploid wheat species (T. dicoccoides, T. dicoccum, T. carthlicum and T. durum, AABB). Eight out of 18 lines showed significantly lower copies than the sum of their parents and seven lines were equal to the sum, suggesting that polyploidy caused loss of Revolver. Members of the Revolver family also showed structural variation in the 5′ region, especially in length. Revolver did not share any similarity with autonomous transposable elements. However, the long terminal repeats (LTRs) of the non-autonomous large retrotransposon derivative (LARD) in barley, showed 60% homology to both 5′ and 3′ ends of some variants of Revolver. LARD LTRs lack the Revolver region from the first exon to the middle of the first intron resulting in non-coding sequences. Evolutionary relationships between Revolver and LARD are discussed.
Drought stress is one of the most severe abiotic stresses that cause the loss of crop yield. The cuticle protects the leaf from dehydration in the face of drought stress. The barley cuticle mutant eibi1 is highly drought sensitive. Here, we describe the fine-scale genetic mapping of the eibi1 locus, based on a cv. Morex × eibi1 F2 population of 1,682 individuals. Barley-rice synteny was exploited to identify markers for mapping and to identify candidate genes for Eibi1. The target segment of chromosome 3H is perfectly collinear with the equivalent region on rice chromosome 1. Marker enrichment delimited eibi1 to a 0.11 cM barley region defined by the interval BI958842–Os01g0176800*, which in rice consists of a 112.8 kbp segment. Gene prediction revealed that this rice segment harbours 16 genes. Of them, five (Os01g0177100, Os01g0177200, Os01g0177900, Os01g0178200 and Os01g0178400) were proposed as candidate genes of Eibi1.
Seed dormancy in wild barley enables drought escape by preventing germination during the hot summer in arid environments. Dormancy in cultivated barley has different effects: it can delay the malting process and/or it can prevent pre-harvest sprouting. Thus, cloning dormancy genes in barley will contribute to understanding the domestication process and it will facilitate optimizing the trait for efficient agronomic and industrial uses. Rates of seed germination were used to evaluate dormancy on physiologically matured grain samples that were dried and stored frozen until use. With this phenotypic scoring procedure, many genetic factors controlling seed dormancy has been reported as quantitative trait loci (QTL). Of these QTL, one at the centrometic region of chromosome 5H (Qsd1) has been most frequently identified and shows the largest effect across mapping populations. We also identified this QTL using the EST map based on Haruna Nijo (H. vulgare ssp. vulgare) crossed with wild barley H602 (H. vulgare ssp. spontaneum). We have derived both doubled haploid and recombinant chromosome substitution lines (RCSLs) from this cross. At least four QTLs are segregating in this germplasm. RCSLs having only the Qsd1 segment of wild barley in a Haruna Nijo genetic background were identified and 910 BC3F2 plants were scored for dormancy. In these lines, segregation for dormancy fit a mono-factorial ratio. These germplasm resources are appropriate for map based cloning of Qsd1. Strategies for cloning Qsd1 with these resources are discussed.
Elymus nutans L. (StHY, 2n = 6x = 42) is extensively selected from the natural population and domesticated as perennial grass forage in the Qinghai-Tibet plateau in China due to its high tolerance to environmental stresses, such as cold and drought. Karyotyping was conducted in 12 randomly selected plants by sequential fluorescence in situ hybridization (FISH) and genomic in situ hybridization (GISH). GISH discriminated St, H and Y genomes, indicating that E. nutans has retained its ancestral genome, and large chromosomal rearrangements have not occurred. However, FISH using an AGG satellite and Afa-family repetitive sequences, revealed marked variation in the signalling patterns of most of the chromosomes. Many of the plants carried chromosomes with a specific pattern in the homozygous state, indicating that self-pollination or sib-crossing occurs in small populations during selection for domestication. In addition, several intergenomic translocations appeared, possibly caused by homoeologous chromosome recombination. The nature of the polymorphisms seen in the chromosomes of the domesticated population of E. nutans is discussed.
Flowers which show cleistogamy (CL) remain closed during pollen shedding, and thus are predominantly self-pollinated. CL in barley is controlled either by the single, multi-allelic gene cly1 located on the long arm of chromosome 2H, or by two closely linked, epistatic genes (cly1 and Cly2). Here, we have taken advantage of the co-linearity which exists between chromosome 2H of barley and rice chromosome 4 to generate de novo markers targeted to the CL region, and these have been used to construct a localized high resolution genetic map. While synteny is largely conserved in this region, the critical 18 cM barley segment appears to be inverted with respect to the equivalent 1.6 Mb physical stretch of the rice genome. The cly1 locus was located in a 0.76 cM region of barley genetic map, and rice orthologue of cly1 (if there is one) is one of the 11 genes predicted to lie within 90 kb interval of rice genome.
P23k is a monocot-unique protein that is highly expressed in barley. Our previous loss-of-function studies in barley leaves indicated that P23k, localized to tissues where cell wall polysaccharides accumulate, might contribute to secondary wall formation in the leaf. However, the P23k loss-of-function analysis was limited to the leaf, which is a vegetative organ. Considering the involvement of P23k in secondary wall formation, a dramatically altered phenotype is expected in the stem of P23k gene-silenced barley, where marked secondary wall deposition occurs during the reproductive growth stage. To test this hypothesis, barley striped mosaic virus-based virus-induced gene silencing of P23k was performed. Abnormal tiller formation and arrested intercalary elongation were observed in P23k-silenced barley. From these results, we speculated that cell wall architecture was altered by P23k gene silencing. Consistent with this idea, we observed a marked decrease in the amount of cell wall polysaccharides stained with calcofluor and down-regulation of the cellulose synthase-like CslF6 gene involved in (1,3;1,4)-β-D-glucan synthesis. Taken together, these results suggest that P23k is possibly involved in determining secondary wall architecture and contributes to tiller formation and intercalary elongation in barley.
The ability of plants to exclude sodium from the shoot is one of the major components of salinity tolerance. In this study, considerable variability in sodium exclusion within different species is demonstrated. The diploid species T. monococcum revealed a large (50-fold) variability in sodium exclusion in contrast to T. urartu, which was significantly less variable (10-fold). These species with the A genome are known to be salt sensitive, whilst T. (Aegilops) tauschii, a diploid species with the D genome, was very salt tolerant, but had only moderate variability in sodium exclusion (10-fold). The tetraploid species T. turgidum ssp. durum (both cultivated and landraces) and wild emmer T. dicoccoides (all with the AB genome) showed a range of variability in both salinity tolerance and sodium exclusion. The general pattern (from most sensitive and with highest Na+ accumulation) was as follows: durum (cultivated) < durum (landraces) < wild emmer. Cultivated durum wheats had minimal or no variability, whereas landraces of durum wheats had greater variability, two excellent genotypes having been identified which combine very low sodium accumulation with very high salinity tolerance. Wild emmer was extremely variable. Hexaploid bread wheat, T. aestivum with the ABD genome, is known to be more salt tolerant, having an effective mechanism for sodium exclusion but only low variability.
The crossability of common wheat with alien species, e.g., rye, wild and cultivated barley, is known to be controlled by the Kr gene family. The reproduction barrier caused by Kr genes decreases hybrid seed set; however, the molecular mechanism is still unclear. We attempted to localize the QTLs controlling the crossability of wheat in wheat-rye crosses by using molecular markers on wheat chromosome 5B on which the most effective Kr gene is known to be located. QTL mapping was carried out using the F7 population derived from a cross between Chinese Spring (high crossability) and a chromosome substitution line of Chinese Spring which has its chromosome 5B of Cheyenne (low crossability), and pollinated with rye cv. Petkus. In this population, a major QTL region controlling crossability with rye was detected on the locus closely linked to a SSR marker, Xgwm443, on the short arm of chromosome 5B which was supposed to be Skr locus.
We describe a new genus in the Triticeae, Connorochloa Barkworth, S.W.L. Jacobs, & H.Q. Zhang, which currently contains only one species, Connorochloa tenuis (Buchanan) Barkworth, S.W.L. Jacobs, & H.Q. Zhang. Connorochloa differs from all other members of the Triticeae in having a peduncle that elongates greatly after anthesis, causing the culms to become prostrate at maturity, and in combining the H, W, St, and Y genomes. Morphologically, it most closely resembles species of Anthosachne, which are hexaploids having the St, Y, and W genomes, but differs from all of them in the peduncle character and having longer awns on the upper glumes and from most species in its combination of narrow leaf blades and long, straight awns.
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