August 28, 2012, Shenzhen, China - The international research team led by Chinese Academy of Agricultural Sciences and BGI have completed the genome sequence and analysis of a diploid cotton-- Gossypium raimondii. The cotton genome provides an invaluable resource for the study and genetic improvement of cotton quality and output, and sheds new lights on understanding the genetic characteristics and evolutionary mechanism underlying cotton and its close relatives. The study was published online in Nature Genetics. (http://www.nature.com/ng/journal/vaop/ncurrent/full/ng.2371.html).
Cotton, also known as "white gold", is an important cash crop worldwide. Its fiber is one of the oldest fibers under human cultivation, which traces over 7,000 years old recovered from archaeological sites. The cotton production provides income for approximately 100 million families, and approximately 150 countries are involved in cotton import and export. Additionally, in scientific research, cotton also serves as an excellent model system for studying polyploidization, cell elongation and cell wall biosynthesis.
In this study, researchers sequenced the genome of G. raimondii by the next-generation sequencing technology, yielding a draft cotton genome with 103.6-fold genome coverage. Over 73% of the assembled sequences were anchored on 13 G. raimondii chromosomes. They identified 2,355 syntenic blocks in the G. raimondii genome, and found that approximately 40% of the paralogous genes were present in more than 1 block, which suggests that this cotton genome has undergone substantial chromosome rearrangement during its evolution.
Through comprehensive comparison and analysis, researchers observed that one paleohexaploidization event occurred in the G. raimondii genome at approximately 130.8 million years ago, while the event is commonly found in eudicots. They also found the evidence to support a cotton-specific whole-genome duplication event occurred at approximately 13-20 million years ago.
Cotton is known to produce a unique group of terpenoids such as gossypol. The accumulated gossypol and related sesquiterpenoids produced by cotton in pigment glands can be as a resistance against pathogens and herbivores. The majority of cotton sesquiterpenoids are derived from a common precursor which is synthesized by (+)- δ -cadinene synthase (CDN) in gossypol biosynthesis. Through the phylogenetic analysis on G. raimondii and eight other sequenced plant genomes, they found that the cotton, and probably Theobroma cacao, were the only sequenced plant species that possess an authentic CDN1 gene family for gossypol biosynthesis.
Furthermore, the transcriptomic comparison between the fiber-bearing G. hirsutum and the non-fibered G. raimondii demonstrated that three synthases are important for cotton fiber development, including sucrose synthase (Sus), 3-ketoacyl-CoA synthase (KCS) and 1-aminocyclopropane-1-carboxylic acid oxidase (ACO). Meanwhile, the MYB and bHLH transcription factors preferentially expressed in fiber may be useful to explain the molecular mechanisms that are in charge of governing fiber initiation and early cell growth.
Zhiwen Wang, Project Manager at BGI, said, "The completed G. raimondii genome provides a good reference for accelerating the genomic research on tetraploid cotton species such as G. hirsutum and G. barbadense. It also will lay a solid foundation for researchers to further boost cotton quality and productivity by comprehensively exploring the genetic mechanisms underlying cotton fiber initiation, gossypol biosynthesis and resistance against pathogens and herbivores."
BGI was founded in Beijing, China on September 9th, 1999 with the mission of being a premier scientific partner to the global research community. The goal of BGI is to make leading-edge genomic science highly accessible through its investment in infrastructure that leverages the best available technology, economies of scale, and expert bioinformatics resources. BGI, and its affiliates, BGI Americas, based in Cambridge, MA and BGI Europe, based in Copenhagen. Denmark, have established partnerships and collaborations with leading academic and government research institutions as well as global biotechnology and pharmaceutical companies, supporting a variety of disease, agricultural, environmental, and related applications.
BGI has established a proven track record of excellence, delivering results with high efficiency and accuracy for innovative, high-profile research which has generated over 200 publications in top-tier journals such as Nature and Science. These accomplishments include sequencing one percent of the human genome for the International Human Genome Project, contributing 10 percent to the International Human HapMap Project, carrying out research to combat SARS and German deadly E. coli, playing a key role in the Sino-British Chicken Genome Project, and completing the sequence of the rice genome, the silkworm genome, the first Asian diploid genome, the potato genome, and, most recently, 1000 genomes and human Gut metagenome. For more information about BGI, please visit www.genomics.cn.
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