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[BEIJING] Scientists have sequenced the genome of a genetically modified (GM) papaya, a step that could benefit both cultivation of the fruit and the understanding of fruit tree genomics.

As the first GM virus-resistant fruit tree to be sequenced, the researchers also hope it will further the understanding of GM genomes and the effects of inserted genes.

Led by Wang Lei at China-based Nankai University and Ray Ming from the US-based University of Illinois at Urbana-Champaign, researchers from 22 US and Chinese institutions published the draft genome in Nature today (24 April).

Rich in provitamin A, vitamin C, potassium, magnesium and fibre, papaya is one of the most nutritious cultivated fruits. It is grown across the globe's tropical regions and recommended for preventing vitamin A deficiency in children.

The researchers sequenced over 90 per cent of papaya's genome. They found that it has significantly fewer genes than other sequenced flowering plants, and that the plant has not experienced major genetic change across its genome in the last 72 million years.

When compared with other flowering plants, the researchers also found genetic changes associated with enhanced fruit production, adaptation to tropical day lengths and attracting seed dispersal agents such as animals.

The 'SunUp' papaya used by the scientists contains randomly inserted genes to give it immunity to the papaya ringspot virus, which reduces papaya yields and fruit quality.

"When targeted insertion becomes possible, the draft genome sequence will certainly provide guidance to the targeting sites," Ming told SciDev.Net.

Lai Zhongxiong, director of the Institute of Subtropical Fruits at Fujian University of Agriculture and Forestry, welcomes the study, saying it could offer information on cultivating papaya varieties with diversified traits such as higher yields and tolerance in extreme environments.

"More importantly, so far most genetic insertions in GM plant breeding take place randomly. The method used in this study may help researchers better understand the role of the inserted genes in the GM crops, easing safety concerns on them," Lai told SciDev.Net.

The draft genome sequence has been added to the GenBank database and is freely available to researchers worldwide.

Link to full paper in Nature


Nature, 452, 991 (2008)