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Cereal Genomics
Cereal cropFAO's definition of cereals describes these plants as annual plants
which generally belong to the gramineous family, producing grains that are used for food, feed, seed and production of industrial products.
Cereal Crops:RiceWheat, Corn or maizeBarleyMillet SorghumOat Rye
introductionThe economic and scientific importance of the
cereals has motivated a rich history of research into their genetics, development, and evolution.
The nearly completed sequence of the rice genome is emblematic of a transition to high-throughput genomics and computational biology that has also pervaded study of many other cereals.
The relatively close (ca. <50 million years old) relationships among morphologically diverse cereals native to environments that sample much of global geographic diversity make the cereals particularly attractive for comparative studies of plant genome evolution.
Using the rapidly growing capabilities of several informatics resources, genomic data from model cereals are likely to be leveraged tremendously in the study and improvement of a wide range of crop plants that sustain much of the world's population
Japonica and Indica
The sequence of the japonica cultivar Nipponbare was recently completed by a consortium of 10 countries, which comprised the International Rice Genome Sequencing Project (IRGSP)
Using the rapidly growing capabilities of several informatics resources, genomic data from model cereals are likely to be leveraged tremendously in the study and improvement of a wide range of crop plants that sustain much of the world's population
Rice:Rice is considered a model cereal crop
because it has a relatively small genome size as compared with other cereals, a vast germplasm collection, an enormous repertoire of molecular genetic resources, and an efficient transformation system.
The scientific value of rice is further enhanced with the elucidation of the genome sequence of the two major subspecies of cultivated rice, Oryza sativa ssp.
Conti…..For this reason and because of its small size, rice
was promoted as a model and was chosen to be the first cereal genome sequenced.
Further, the development of large EST collections and the first inter- and intra-specific comparative studies of BAC sequences from maize, sorghum, rice, wheat and barley have increased the resolution of comparative analyses and have shown that a number of rearrangements disrupting microcolinearity have occurred during the evolution of the cereal genomes in the past 50–70 million years.
development of molecular markers, and for identifying the region in the model species that might contain candidate genes responsible for a trait of interest. Rice (2n = 24), having a small genome and great economic significance, was the first grass species selected for genome sequencing
© 2005 Prentice Hall Inc. / A Pearson Education Company / Upper Saddle River, New Jersey 07458
Sequencing of crop-plant genomesReasons for
sequencing rice first Importance as crop
Largest food source for poor
Feeds half of world’s population (3 billion)
Demand likely to increase dramatically
80% of daily calories in Asia come from rice
In Asia alone, demand will increase by at least 35%.
© 2005 Prentice Hall Inc. / A Pearson Education Company / Upper Saddle River, New Jersey 07458
Rice genomeSmallest among grass
genomes (Wheat, oat, rye, Barley, corn)Few repetitive
elementsSynteny with other
grasses (recent evolution from a common ancestor approximately 50–70 million years ago)
Genetic and physical maps
Genomic resourcesOver million ESTs
Efficient transformation
© 2005 Prentice Hall Inc. / A Pearson Education Company / Upper Saddle River, New Jersey 07458
Facts about the rice genomeSize: 430 Mbp (3.3
X Arabidopsis)Number of genes:
approximately 60,000
Repetitive elements: Most in intergenic regions versus in introns in humans
Animals use alternative splicing and plants gene duplication?
© 2005 Prentice Hall Inc. / A Pearson Education Company / Upper Saddle River, New Jersey 07458
Genomics of other cerealsMaize: 3,000 MbpWheat: 5,000 MbpBarley: 16,000
MbpGenome
organizationGenic or gene-rich
islands in the sea of retroposons
© 2005 Prentice Hall Inc. / A Pearson Education Company / Upper Saddle River, New Jersey 07458
Rice and Arabidopsis genomesNo large areas of
synteny80% of Arabidopsis
genes have homologs in rice
Reverse not trueOnly 50% of rice
genes have homologs in Arabidopsis
150–200 million years of divergence (Quick change)
Rice
Arabidopsis
Wheat genome:A U.S. National Science Foundation-funded wheat
expressed sequence tag (EST) project has been studying the structure and function of the expressed portion of the wheat genome by mapping wheat unigenes to individual chromosome regions. Representative ESTs, each belonging to one of the unigenes (http://wheat.pw.usda.gov/NSF/progress_mapping.html) were used for mapping in the wheat genome utilizing 101 wheat deletion stocks, each of which contain a deletion of a defined part of a chromosome (Endo and Gill 1996), referred to as deletion mapping. As of November 2002, over 100,000 ESTs from various tissues of wheat at different stages of development have been sequenced, and 4485 wheat unigenes have been deletion mapped by this project.
Cereal Genome SizesSorghum 1000 MbMaize 3000 MbBarley 5000 MbWheat 16,000 MbRice 420 Mb
Conti….The wheat whole genome sequence data
provides direct access to all 96,000 genes and represents an essential step towards a systematic understanding of biology and engineering .
The cereal crop for valuable traits. Its implications in cereal genetics and breeding includes the examination of genome variation, association mapping using natural populations.
Maize genome:The 21st century finds maize in the process of
being sequenced. With an estimated 2300-2600 Mb of chromosomal DNA (6× rice and 20× Arabidopsis), of which at least 60% is retrotransposon.
• the maize genome has initially been “filtered” to enhance its production(Rabinowicz et al. 1999) or low-repeat (Peterson et al. 2002a; Yuan et al. 2003) sequence—before shotgun sequencing (Whitelaw et al. 2003)
Cont…..Maize (n = 10) is a recent domesticate of the
tropical grass (Doebley 2004). The most recent maize whole-genome duplication happened approximately 12 Mya (Gaut and Doebley 1997).
Sorghum genome:The most detailed sorghum sequence-tagged site (STS)-
based map is from a cross between Sorghum bicolor (SB) and S. propinquum (SP), comprising 2512 restriction fragment length polymorphism loci that span 1059.2 cM (Bowers et al. 2003).
A total of 865 heterologous probes link the sorghum map to those of Saccharum (sugarcane: Ming et al. 1998), Zea (maize: Bowers et al. 2003), Oryza (rice: Paterson et al. 1995, 2004), Pennisetum (millet, buffelgrass: Jessup et al. 2003), the Triticeae (wheat, barley, oat, rye), Panicum (switchgrass: Missaoui et al. 2005), and Cynodon (bermudagrass: C. Bethel, E. Sciara, J. Estill, W. Hanna, and A.H. Paterson, in prep.).
Sorghum was the first plant for which a BAC library was reported (Woo et al. 1994). Physical maps of both SB and SP have been constructed and genetically
The consensus comparative map of seven grass species shows how the genomes can be aligned in terms of "rice linkage blocks" (Gale & Devos, 1998). A radial line starting at rice, the smallest genome and innermost circle, passes through regions of similar gene content in the other species. Therefore a gene in one grass species has a predicted location in a number of other grass species. This observation has driven much sharing among researchers working on the various grass species (Phillips & Freeling, 1998).
Conclusion:It can help us in comparative genomics.Itcan also help in crop improvement.It can also help for maintanace of better
quaity crops.Overall impact on the quality of life on earth.