(Xinhua)
Updated: 2008-04-24 07:14

WASHINGTON -- A broad collaboration of research institutions in the U.S. and China has produced a first draft of the papaya genome, University of Illinois announced on Wednesday.

This draft, which spells out more than 90 percent of the plant' s gene coding sequence, sheds new light on the evolution of flowering plants. The findings appear as the cover article in the April 24 issue of journal Nature.

Because it involves a genetically modified plant, the newly sequenced papaya genome offers the most detailed picture yet of the genetic changes that make the plant resistant to the papaya ringspot virus (PRSV).

Papaya is now the fifth angiosperm (flowering plant) for which detailed genome information is available. The others are Arabidopsis, rice, poplar and grape.

The new findings indicate that the papaya genome took a different evolutionary path after its divergence from that of Arabidopsis about 72 million years ago, said Ray Ming, a University of Illinois professor of plant biology and co-lead author on the study.

Papaya is one of the most nutritious fruits known. Its melon- like flesh is high in provitamin A, vitamin C, flavonoids, folate, pantothenic acid, potassium, magnesium and fiber.

The papaya plant also produces papain, a digestive enzyme that is used in brewing, meat tenderizing, and in some cosmetics and pharmaceutical products. Today it is cultivated in tropical and subtropical regions of the world.

PRSV affects papaya production throughout the world. The virus interferes with the plant's ability to photosynthesize. Affected plants are stunted and often produce deformed and inedible fruit.

Using a technique developed in 1986 that involved randomly inserting a viral coat protein gene into a plant to give the plant immunity to the virus, in the early 1990s U.S. scientists developed a transgenic papaya that was resistant to PRSV.

The new study has found that the transgenic insertions occurred in only three places in the papaya genome, and that no nuclear genes were disrupted.