http://english.cri.cn/6909/2012/03/22/2021s688497.htm

Scientists Sequence Sweet Orange Genome

2012-03-22 16:54:10 Xinhua Web Editor: Zhangxu

Chinese scientists have sequenced the genome of the sweet orange (Citrus sinensis), an achievement expected to help scientists understand the complex genetic make-up of the crop in order to improve its quality and yield, according to researchers with Central China Agricultural University in Wuhan, capital of Hubei province.

After a year's effort, a team of horticulture, genomics and bioinformatics experts from the university successfully assembled and annotated the genome sequence of the plant, marking the first time that Chinese scientists have independently determined the genome sequence of a fruit crop.

Deng Xiuxin, an academician with the Chinese Academy of Engineering and the leader of the research team, said that the sequencing of the genome marks the establishment of an ideal research platform for biotechnology and genetic engineering in China, and it is also gravely important for improving breeding and upgrading the crop's industrial competitiveness.

Breeds of citrus are among the most widely grown fruit crops in the world. The sweet orange, which originated in China, is the most commonly grown fruit tree in the world, and its production accounts for about 60 percent of total citrus production.

The sweet orange, mostly poly-embryonic, is highly heterozygous, which means it has dissimilar pairs of genes for any hereditary characteristic, and is plagued by sterility. Therefore, determining its genetic make-up can provide a sound scientific basis for genetic and breed development work, according to Xu Qiang, an expert with Central China Agricultural University.

China is the world's largest grower of citrus, and Chinese people have been cultivating citrus crops for 4,000 years. Statistics from the Ministry of Agriculture show that China produced 26.45 million tonnes of citrus across 2.21 million hectares in 2010.

Of the more than 80 types of citrus species grown in China, 40 percent are not native to China, and half of the country's fruit production is generated from foreign breeds, Deng said, adding that China has been eager to see breakthroughs in the genetic research of citrus in order to speed up the improvement of China's own citrus breeds.

Deng compared sequencing the genome of the sweet orange to opening the "black box" of the crop's life activities, a move that could facilitate the improvement of many of the fruit's traits, including color, taste, yields and disease resistance.

Xu said the researchers launched a website for the sweet orange genome sequence (http://citrus.hzau.edu.cn) on Wednesday to provide free data analysis for academic research.

The world's first human genome sequence map was finished in June 2000. From 2000 to 2009, scientists across the world have drawn whole genome sequence maps for 1,100 species, averaging 118 a year.

Chinese scientists have completed genome sequencing for rice, domesticated silkworms, chickens, oysters as well as endangered animals such as the giant panda and Tibetan antelope.

http://www.chinadaily.com.cn/m/hubei/2012-04/10/content_15013561.htm

Decoding the genome sequence of oranges
( chinadaily.com.cn )
Updated: 2012-04-10

Uncovering the genome sequence assembly of an orange has been accomplished by a team of scientists led by Professor Deng Xiuxin, a member of the Chinese Academy of Engineering, and Professor Ruan Yijun, a member of National Thousand Talents Program, from Huazhong Agricultural University.

The scientists studied the horticulture, genomics and bioinformatics, assembled and annotated it to obtain a high quality genome.

The country produces the most citrus crops along with total acreage in the world. Oranges account for about 60 percent of citrus production both as fresh fruit and processed juices. They are mostly polyembryony, male or female sterile and highly heterozygous.

These characteristics hindered genetic and breeding development. A complete genome sequence would provide a molecular framework for genetic breeding and improvements.

Oranges are diploids, with a haploid chromosome x=9. It has a relatively small genome about 367 Mb, which is sequenced by a WGS shotgun strategy, with total sequencing data of about 200 G. The assembly covers 87 percent of the estimated genome with Scaffold N50=1.7Mb. The genome was annotated with 29,655 protein-coding genes.

The genome sequence has been assigned to nine chromosomes by a genetic marker and FISH analyses. Comparative analyses showed that about 81 percent and 83 percent of orange genes were shared with the grape and strawberry respectively.

China is considered to be the native region of citrus. Domestic citriculture could be traced back 4,000 years ago when it first appeared in the book, 'YuGong' where mandarins and pummelos were listed as tributes to the Emperor Da Yu of the Xia Dynasty in the 21st century BC.

The country holds abundant citrus cultivated species or varieties, including mandarins, tangerines, oranges, pummels, lemons, kumquat and citrons.

The domestic citrus sector has developed rapidly in the past 30 years with total acreage of 2.21 million hectares and production of 26.45 million tons in 2010.

The orange genome will facilitate a better understanding of citrus biological studies and improve the citrus traits that include the mature time, fruit color, aroma and flavor in the years ahead.

Sweet orange genome database: http://citrus.hzau.edu.cn, the data are free for academic use.

Edited by Fu Bo and Tom McGregor