To maximise yield potential in any environment, wheat cultivars must have an appropriate flowering time and life cycle duration, which fine tunes the life cycle to the target environment. For plant breeders to produce...To maximise yield potential in any environment, wheat cultivars must have an appropriate flowering time and life cycle duration, which fine tunes the life cycle to the target environment. For plant breeders to produce such varieties by conventional plant breeding combined with marker assisted selection, or by genetic engineering, a detailed knowledge of the genetic control of the key components is required. Genetic analysis in wheat using precise genetic stocks, particularly substitution lines and recombinant substitution lines, has revealed that there are three genetically independent systems controlling life cycle duration in wheat, namely those controlling vernalization response ( Vrn genes), photoperiod response ( Ppd genes) and developmental rate (“earliness per se”,Eps genes). This paper discusses our current knowledge of these systems and their role in modifying life cycle duration and yield potential. In addition, comparative mapping of these genes in other Triticeae species, particularly barley, is indicating new target genes for discovery in wheat, and comparative mapping with rice is indicating that rice may have orthologues of Triticeae flowering time genes, and, hence rice may provide a strategy for cloning Vrn and Ppd genes using rice molecular tools. The major genes controlling photoperiod response in wheat, the Ppd 1 genes, have been shown to be located on the homoeologous group 2 chromosomes. These have been shown to have dramatic effects on yield potential in different environments. In temperate northern latitudes it is advantageous to have late spring flowering, and hence a long vegetative period, mediated by response to longer day length, and hence varieties need to possess photoperiod sensitive alleles. In autumn sown spring wheats in sub tropical regions, or southern European winter wheats, it is advantageous to flower early in the spring to complete the life cycle before desiccating summer temperatures, and, hence, varieties possess strong alleles for photoperiod insensitivity, such as Ppd D1a . These genes on 2A, 2B and 2D are homoeologous to a gene on barley chromosome 2H, Ppd H1 .However,mapping in barley also indicates that there are photoperiod response loci on barley chromosomes 1H and 6H, indicating that homoeologous series should exist on wheat group 1 and 6 chromosomes. These have not yet been mapped. The need for vernalization determines the difference between winter and spring wheats.The major genes controlling vernalization response have been located both genetically and physically on the long arms of the homoeologous group five chromosomes. These genes are homoeologous to each other and to the vernalization genes on chromosomes 5H of barley and 5R of rye. By using rice RFLP probes and a rice mapping population it was shown that a region homoeologous to the Triticeae Vrn 1 region exists on rice chromosome 3. This finding was confirmed using deletion lines, where probes from rice chromosome 3 and probes co segregating with Vrn A1 all mapped in deletions associated with a flowering time effect. Comparative analysis also indicates that another series of vernalization response genes may exit on chromosomes of homoeologous group 4 (4B, 4D, 5A), and mapping studies in Triticum monococcum support this. Apart from the ability to protect plants from winter kill by delaying reproductive development, the Vrn genes do not appear to have major effects on yield potential once vernalization requirement is satisfied. Nevertheless, in some environments, lengthening of the life cycle by introducing vernalization sensitivity can increase the canopy size, and hence, yield potential. In wheat, to date, very few “earliness per se” loci have been located. Only those on chromosomes of homoeologous groups 2 and 3 have been mapped in any detail, and then only as QTL effects and not precisely as major genes. Also, little is currently known on the pleiotropic effects of different alleles on yield potential in different environments. In barley, all展开更多
The John Innes Centre is a major centre for research into the genetics, cytogenetics, molecular biology, pathology and biotechnology of cereals. Most work focuses on wheat, but barley, rye, maize, rice and millet spec...The John Innes Centre is a major centre for research into the genetics, cytogenetics, molecular biology, pathology and biotechnology of cereals. Most work focuses on wheat, but barley, rye, maize, rice and millet species are also studied. Work on cereal cytogenetics is concerned with studying chromosome pairing and transferring new variation, particularly for biotic and abiotic stress resistance, from related alien species into wheat. The transfer of genes for mildew resistance, aluminum tolerance and salt tolerance are recent successes. Particularly significant at the present time is work to clone the gene Ph1 ,responsible for controlling the diploid meiotic behavior of hexaploid wheat. Using a comparative mapping approach and rice molecular tools, possible rice homologues of Ph1 have been isolated on rice BACs, and sequencing of these BACs has identified candidate genes. Work on cereal genomics is concerned with developing new molecular markers, particularly SSR markers, and using these for mapping and fingerprinting European wheat germplasm. Work to develop Single Nucleotide Polymorphism (SNP) systems has been initiated. Additionally, new genomic tools are being developed such as a hexaploid wheat BAC library, and the Department is involved in the ITEC EST sequencing and databasing, and the development of wheat DNA microarray technology. The Department has large projects concerned with identifying new major genes and QTL controlling important agronomic traits using molecular marker mediated forms of genetic analysis and precise genetic stocks, particularly recombinant substitution lines and recombinant doubled haploid populations. Major targets are genes controlling adaptation, drought and salt tolerance, pre harvest sprouting tolerance, bread making and animal feed quality, and adult plant resistance to fungal pathogens. The Department is a major centre for cereal transformation with programs on the genetic engineering of wheat, barley and rice, mainly, at present, using biolistics.A non destructive marker system using the luciferase gene is used routinely, mediated by special JIC developed transformation cassettes. A major component of this work is technology development, where systems for Agrobacterium mediated transformation are being developed so that marker free, clean gene technology can be used. In rice, the major target traits being engineered are for pest and disease resistance into West African varieties, particularly the use of protease inhibitor constructs effective against nematodes, and a homology dependant induced resistance mechanism against rice yellow mottle virus. In barley, quality traits are being modified, such as the introduction of a fungal enzyme to increase starch conversion during the malting process, and a gene for lysine biosynthesis to improve nutritional value. Alongside technology development, molecular analysis of transgene structure, expression, and the physical and genetic mapping of transgenes is being carried out. Work on cereal fungal pathology is concerned with studying pathogen variation and molecular biology, and discovering new host resistance genes against isolates of the major UK fungal pathogens; yellow and brown rust, powdery mildew, Septoria triticii , eyespot and Fusarium species. A mixture of conventional pathology and molecular pathology approaches are used in this work, and a major target is the cloning of avirulence genes in the pathogen and resistance genes in the host, and understanding the mechanisms of virulence and resistance. New genes for resistance to Septoria species on chromosome 7D have recently been mapped. For resistance breeding against Fusarium species, new molecular diagnostic tools have been developed to quantify infection levels using quantitative PCR, so that the effects of specific species on infection levels in the stem base and in the head can be characterized. Details of the work can be viewed at the web site : www.jic.bbsrc.ac.uk.展开更多
文摘To maximise yield potential in any environment, wheat cultivars must have an appropriate flowering time and life cycle duration, which fine tunes the life cycle to the target environment. For plant breeders to produce such varieties by conventional plant breeding combined with marker assisted selection, or by genetic engineering, a detailed knowledge of the genetic control of the key components is required. Genetic analysis in wheat using precise genetic stocks, particularly substitution lines and recombinant substitution lines, has revealed that there are three genetically independent systems controlling life cycle duration in wheat, namely those controlling vernalization response ( Vrn genes), photoperiod response ( Ppd genes) and developmental rate (“earliness per se”,Eps genes). This paper discusses our current knowledge of these systems and their role in modifying life cycle duration and yield potential. In addition, comparative mapping of these genes in other Triticeae species, particularly barley, is indicating new target genes for discovery in wheat, and comparative mapping with rice is indicating that rice may have orthologues of Triticeae flowering time genes, and, hence rice may provide a strategy for cloning Vrn and Ppd genes using rice molecular tools. The major genes controlling photoperiod response in wheat, the Ppd 1 genes, have been shown to be located on the homoeologous group 2 chromosomes. These have been shown to have dramatic effects on yield potential in different environments. In temperate northern latitudes it is advantageous to have late spring flowering, and hence a long vegetative period, mediated by response to longer day length, and hence varieties need to possess photoperiod sensitive alleles. In autumn sown spring wheats in sub tropical regions, or southern European winter wheats, it is advantageous to flower early in the spring to complete the life cycle before desiccating summer temperatures, and, hence, varieties possess strong alleles for photoperiod insensitivity, such as Ppd D1a . These genes on 2A, 2B and 2D are homoeologous to a gene on barley chromosome 2H, Ppd H1 .However,mapping in barley also indicates that there are photoperiod response loci on barley chromosomes 1H and 6H, indicating that homoeologous series should exist on wheat group 1 and 6 chromosomes. These have not yet been mapped. The need for vernalization determines the difference between winter and spring wheats.The major genes controlling vernalization response have been located both genetically and physically on the long arms of the homoeologous group five chromosomes. These genes are homoeologous to each other and to the vernalization genes on chromosomes 5H of barley and 5R of rye. By using rice RFLP probes and a rice mapping population it was shown that a region homoeologous to the Triticeae Vrn 1 region exists on rice chromosome 3. This finding was confirmed using deletion lines, where probes from rice chromosome 3 and probes co segregating with Vrn A1 all mapped in deletions associated with a flowering time effect. Comparative analysis also indicates that another series of vernalization response genes may exit on chromosomes of homoeologous group 4 (4B, 4D, 5A), and mapping studies in Triticum monococcum support this. Apart from the ability to protect plants from winter kill by delaying reproductive development, the Vrn genes do not appear to have major effects on yield potential once vernalization requirement is satisfied. Nevertheless, in some environments, lengthening of the life cycle by introducing vernalization sensitivity can increase the canopy size, and hence, yield potential. In wheat, to date, very few “earliness per se” loci have been located. Only those on chromosomes of homoeologous groups 2 and 3 have been mapped in any detail, and then only as QTL effects and not precisely as major genes. Also, little is currently known on the pleiotropic effects of different alleles on yield potential in different environments. In barley, all
文摘The John Innes Centre is a major centre for research into the genetics, cytogenetics, molecular biology, pathology and biotechnology of cereals. Most work focuses on wheat, but barley, rye, maize, rice and millet species are also studied. Work on cereal cytogenetics is concerned with studying chromosome pairing and transferring new variation, particularly for biotic and abiotic stress resistance, from related alien species into wheat. The transfer of genes for mildew resistance, aluminum tolerance and salt tolerance are recent successes. Particularly significant at the present time is work to clone the gene Ph1 ,responsible for controlling the diploid meiotic behavior of hexaploid wheat. Using a comparative mapping approach and rice molecular tools, possible rice homologues of Ph1 have been isolated on rice BACs, and sequencing of these BACs has identified candidate genes. Work on cereal genomics is concerned with developing new molecular markers, particularly SSR markers, and using these for mapping and fingerprinting European wheat germplasm. Work to develop Single Nucleotide Polymorphism (SNP) systems has been initiated. Additionally, new genomic tools are being developed such as a hexaploid wheat BAC library, and the Department is involved in the ITEC EST sequencing and databasing, and the development of wheat DNA microarray technology. The Department has large projects concerned with identifying new major genes and QTL controlling important agronomic traits using molecular marker mediated forms of genetic analysis and precise genetic stocks, particularly recombinant substitution lines and recombinant doubled haploid populations. Major targets are genes controlling adaptation, drought and salt tolerance, pre harvest sprouting tolerance, bread making and animal feed quality, and adult plant resistance to fungal pathogens. The Department is a major centre for cereal transformation with programs on the genetic engineering of wheat, barley and rice, mainly, at present, using biolistics.A non destructive marker system using the luciferase gene is used routinely, mediated by special JIC developed transformation cassettes. A major component of this work is technology development, where systems for Agrobacterium mediated transformation are being developed so that marker free, clean gene technology can be used. In rice, the major target traits being engineered are for pest and disease resistance into West African varieties, particularly the use of protease inhibitor constructs effective against nematodes, and a homology dependant induced resistance mechanism against rice yellow mottle virus. In barley, quality traits are being modified, such as the introduction of a fungal enzyme to increase starch conversion during the malting process, and a gene for lysine biosynthesis to improve nutritional value. Alongside technology development, molecular analysis of transgene structure, expression, and the physical and genetic mapping of transgenes is being carried out. Work on cereal fungal pathology is concerned with studying pathogen variation and molecular biology, and discovering new host resistance genes against isolates of the major UK fungal pathogens; yellow and brown rust, powdery mildew, Septoria triticii , eyespot and Fusarium species. A mixture of conventional pathology and molecular pathology approaches are used in this work, and a major target is the cloning of avirulence genes in the pathogen and resistance genes in the host, and understanding the mechanisms of virulence and resistance. New genes for resistance to Septoria species on chromosome 7D have recently been mapped. For resistance breeding against Fusarium species, new molecular diagnostic tools have been developed to quantify infection levels using quantitative PCR, so that the effects of specific species on infection levels in the stem base and in the head can be characterized. Details of the work can be viewed at the web site : www.jic.bbsrc.ac.uk.
