Chinese scientists sequence sweet orange genome

Chinese scientists have completed a comprehensive analysis of the draft genome of the sweet orange (Citrus sinensis), the first time a Chinese research team has independently determined the genome sequence of a fruit, according to a paper published online recently in Nature Genetics. This draft genome represents a valuable resource for understanding and improving many important citrus traits in the future.

The assembled sequence covers 87.3% of the estimated orange genome, which is relatively compact, as 20% is composed of repetitive elements. Additional sequencing of two more citrus species and comparative analyses of seven citrus genomes suggests that sweet orange originated from a backcross hybrid between pummelo and mandarin. Focused analysis on genes involved in vitamin C metabolism showed that GalUR, encoding the rate-limiting enzyme of the galacturonate pathway, is significantly upregulated in orange fruit, and the recent expansion of this gene family may provide a genomic basis.

Citrus is a large genus that includes several major cultivated species. In 2009, the global citrus acreage was 9 million hectares and citrus production was 122.3 million tons, which is the top ranked among all the fruit crops. Among the 10.9 million tons (valued at $9.3 billion) of citrus products traded in 2009, sweet orange accounted for approximately 60% of citrus production for both fresh fruit and processed juice consumption.

See the paper in Nature Genetics here.