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Despite rapidly decreasing costs and innovative technologies, sequencing of angiosperm genomes is not yet undertaken lightly. Generating larger amounts of sequence data more quickly does not address the difficulties of sequencing and assembling complex genomes de novo. The cotton (Gossypium spp.) genomes represent a challenging case. To this end, a coalition of cotton genome scientists has developed a strategy for sequencing the cotton genomes, which will vastly expand opportunities for cotton research and improvement worldwide.
WHY SEQUENCE COTTON GENOMES?
Cotton is the world's most important natural textile fiber (Fig. 1A) and a significant oilseed crop. The seed is an important source of feed, foodstuff, and oil. World consumption of cotton fiber is approximately 115 million bales or approximately 27 million metric tons per year (National Cotton Council, http://www. cotton.org/, 2006). Genetic improvement of fiber production and processing will ensure that this natural renewable product will be competitive with petroleumderived synthetic fibers. Moreover, modifying cottonseed for food and feed could profoundly enhance the nutrition and livelihoods of millions of people in foodchallenged economies.
Cotton production provides income for approximately 100 million families, and approximately 150 countries are involved in cotton import and export. Its economic impact is estimated to be approximately $500 billion/year worldwide. China is the largest producer and consumer of raw cotton, but more than 80 countries, including Australia, some African countries, India, Pakistan, the United States, Mexico, and Uzbekistan, also produce cotton. The United States is the second largest producer, and grows cotton worth approximately $6 billion/year for fiber and approximately $1 billion/year for cottonseed oil and meal. Cotton is a major economic driver for some developing countries, like Uzbekistan, which annually produces approximately 4 million tons of raw cotton and exports fiber worth approximately $900 million.
Cotton fiber is an outstanding model for the study of plant cell elongation and cell wall and cellulose biosynthesis (Kim and Triplett, 2001). Each seed has approximately 25,000 cotton fibers, each of which is a single and greatly elongated cell from the epidermal layer of the ovule (Fig. 1B). The fiber is composed of nearly pure cellulose, the largest component of plant biomass. Compared to lignin, cellulose is easily convertible to biofuels. Translational genomics of cotton fiber and cellulose may lead to the improvement of...