Wheat Clones Research Articles

Map-based isolation of disease resistance genes from bread wheat: cloning in a supersize genome

The genome of bread wheat is hexaploid and contains 1.6 x 10 10 bp of DNA, of which more than 80% is repetitive sequences. Its size and complexity represent a challenge for the isolation of agronomically important genes, for which we frequently know only their position on the genetic map. Recently, new genomic resources and databases from genome projects have simplified the molecular analysis of the wheat genome. The first genes to be isolated from wheat by map-based cloning include three resistance genes against the fungal diseases powdery mildew and leaf rust. In this review, we will describe the approaches and resources that have contributed to this progress, and discuss genomic strategies that will simplify positional cloning in wheat in the near future.

Distribution of genes and recombination on wheat homoeologous group 6 chromosomes: a synthesis of available information

Presence of genes in gene-rich regions on wheat chromosomes has been widely reported. However, there is a lack of information on the precise characterization of these regions with respect to the distribution of genes and recombination. We attempted to critically analyze the available data to characterize gene-rich regions and to study the distribution of genes and recombination on wheat homoeologous group 6 chromosomes which are a reservoir of several useful genes controlling traits of economic importance. Consensus physical and genetic linkage maps were constructed for homoeologous group 6 using physical and genetic mapping data. Five major gene-rich regions were identified on homoeologous group 6 chromosomes, with two on the short and three on long arm. More than 90% of marker or gene loci were present in these five gene-rich regions, which comprise about 30% of the total physical chromosomal length. The gene-rich regions were mainly present in the distal 60% regions of the chromosomes. About 61% of the total loci map in the most distal regions which span only about 4% of the physical length of the chromosome. A range of sub-microscopic regions within each gene-rich region were also identified. Comparisons of the consensus physical and genetic linkage maps revealed that recombination occurred mainly in the gene-rich regions. Seventy percent of the total recombination occurred in the two most distally located regions that span only 4% of the physical length of the chromosomes. The relationship of recombination to the gene-rich region is not linear with distance from the centromere, especially on the long arm. The kb/cM estimates for group 6 chromosomes ranged from 146 kb in the gene-rich to about 10 Mb in the gene-poor region. The information obtained here is vital in understanding wheat genome structure and organization, which may lead in developing better strategies for positional cloning in wheat and related cereals.

Cloning and Structural Analysis of Wheat cDNAs Encoding Ndr Protein Kinase Homolog by Data Mining of the EST Database KOMUGI

In order to gain a better understanding of the nature of nuclear dbf-related (Ndr) protein kinase homologs in monocots, three cDNA clones were isolated from common wheat (Triticum aestivum) by data mining of expressed sequence tag (EST) databases, and their primary structure was determined by reverse transcription-polymerase chain reaction (RT-PCR), 5′-rapid amplification of cDNA ends (RACE), and nucleotide sequencing. Deduced amino acid sequences of the cDNA clones contained all 12 highly conserved subdomains of the eukaryotic Ser/Thr protein kinase, including the ATP-binding site (in subdomain I-II) and the Ser/Thr protein kinase active-site (in subdomain VI). The sequences also contained an insert of 56 amino acids between subdomains VII and VIII, and three conserved Ser/Thr residues, being characteristic of the Ndr family of eukaryotic protein kinases. A sequence comparison among cDNAs from wheat and those from ancestral diploid species (T. boeoticum, Aegilops speltoides and Ae. squarrosa) revealed that at least three homeologous genes were expressed in hexaploid wheat. The results confirmed the usefulness of current EST databases including KOMUGI for gene cloning of wheat, since the use of specific primers designed with information about EST sequences has considerably facilitated the cloning of rare cDNAs such as Ndr.

Sivb 2003 Congress Symposium Proceeding: Mutation- and Transposon-Based Approaches for the Identification of Genes for Pre-Harvest Sprouting in Wheat

This article reviews techniques for gene identification and cloning in allohexaploid bread wheat (Triticum aestivum L.). Gene identification and cloning in wheat are complicated by the large size and high redundancy of the genome. Both classical mutagenesis and transposon tagging are important tools for the study of grain dormancy and plant hormone signaling in wheat. While classical mutagenesis can be used to identify wheat mutants with altered hormone sensitivity, it can be difficult to clone the corresponding genes. We review the techniques available for gene identification in wheat, and propose that transposon-based activation tagging will be an important tool for wheat genetics.

An investigation of the differential performance of clones of the aphid Sitobion avenae on two host species.

Individuals of the grain aphid Sitobion avenae were collected from wheat and cocksfoot stands around Hampshire, UK, during March and April 1994. Eight wheat and eight cocksfoot aphid clones were chosen on the basis of readily distinguishable RAPD-PCR fingerprint profiles. The performances (weight, fecundity and survival) of successive generations of each of these clones were then carefully monitored in the laboratory as new generations of aphids were transferred either to winter wheat or to cocksfoot in planned sequences. Even those clones that were originally caught on the same host showed significant variability in performance. Clones generally performed better on their host of origin than they did on the alternate host, and they performed less well on the alternate host compared to the clones that had originated there. A comparison of the performance of third generation aphids with first generation aphids showed that the experience of the mother in the second generation often influences the subsequent performance of their offspring. As the sequence of host transfers had more effect on the performance of wheat clones than cocksfoot clones, it is likely that wheat clones are more specialised, such that wheat is a satisfactory host for cocksfoot clones but not vice versa. The study provides evidence of genetic variation in performance on host and evidence for clonal adaptation to particular host species. This adaptation may well be a major cause of the observed consistent genetic differentiability of populations of S. avenae found on wheat and roadside grasses in early spring in southern England.

Linked sucrose synthase genes in group-7 chromosomes in hexaploid wheat ( Triticum aestivum L.)

A cDNA library from developing wheat endosperm was screened for sucrose-synthase clones using a maize cDNA probe corresponding to the Sh1 locus under non-stringent conditions. Five positive clones were isolated and initially classified into two types on the basis of their relative ability to hybridize with the probe and of their partial restriction maps. Determination of the nucleotide sequences indicated homology between the two types of wheat clones, with type 1 showing higher homology to the maize Sh1 locus than to type-2 sequences. The inserts cloned in plasmids pST8 (type 1) and pST3 (type 2) were used as probes to determine the chromosomal locations of the two types of genes. DNAs from compensated nulli-tetrasomic and ditelosomic lines of wheat cultivar Chinese Spring were cleaved with EcoRI and analysed in Southern blots. DNA segments of the two types were thus identified in the short arms of chromosomes 7A, 7D, and, possibly, 7B. The two types of linked loci have been designated Ss1 and Ss2, respectively.

Identification of barley and wheat cDNA clones related to the high- Mr polypeptides of wheat gluten

We have identified 3 cDNA clones related to the high- M r group of storage proteins in barley endosperm, the D-hordeins. A cDNA library has been constructed from wheat endosperm poly(A +)-RNA and screened using one of the D-hordein cDNA clones. Two wheat clones which cross-hybridised to the barley clone have been identified, by hybrid-release translation and nucleotide sequence analysis, as partial copies of mRNAs encoding the high- M r gluten polypeptides of wheat.