The smell of durian has been described by some to turpentine and onions, garnished with a sweaty gym sock. The green, spiky fruit is banned from public transportation and many hotels in south-east Asia because of its characteristic and pungent smell. But where does it get its scent from? A team of researchers in Singapore, Malaysia and Hong Kong sequenced the durian genome to find out.
Just like many people in South-East Asia, Professor Bin Tean Teh loves the tropical delicacy, which is known as the “king of fruit”.
“It has a very rich, creamy taste. To us, it’s like a heavenly smell and it melts in your mouth,” said Professor Bin, a cancer researcher at Duke-NUS Medical School in Singapore, whose team published the genome sequence on October 9 in Nature Genetics.
[ihc-hide-content ihc_mb_type=”show” ihc_mb_who=”2,3,5″ ihc_mb_template=”1″ ]“We love durian. And, coupled with our scientific curiosity, we felt that it would be great to look at it. We wanted to be able to answer some of the obvious questions regarding this fruit, for example its strong smell,” Bin was quoted as saying by Popular Science, American bi-monthly magazine.
The researchers specifically sequenced the Musang King Durio zibethinus, a popular durian species, and found its genome contained almost a billion base pairs—those are the As, Cs, Ts and Gs that make up the letters of the DNA encyclopedia.
Among the 30 known species in the Durio genus, D. zibethinus is the most prized as a major Southeast Asian food crop. The three leading durian-producing countries are Thailand, Malaysia, and Indonesia, with more than 250,000 ha cultivated in 2008.
The team found around 46,000 genes in the durian’s full DNA sequence whic is twice as many as the human genome — and discovered its heritage can be traced back 65 million years to the cacao plant, from which chocolate is made.
The researchers focused on a particular gene that regulates the production of sulphur compounds, which give off the pungent smell.
The durian fruit’s cells produced more of the volatile sulphur compound than the rest of the plant did, like one enzyme called methionine gamma-lyase (MGL).
A study of gene expression showed that sulphur- and flavour-related pathways were switched on more strongly in the Musang King when compared with two other varieties, or cultivars, of tropical durian, including the sweeter Monthong type.
“Theoretically you could knock out this MGL gene. Then you would get a much lesser smell,” said Bin.
Ahimsa Campos-Arceiz, a tropical ecologist at the University of Nottingham Malaysia Campus in Semenyih said that the latest research could help in the development of tests that can distinguish between more than 200 different varieties of tropical durian, which command a wide range of prices.
It could also aid in the cultivation of “new and interesting” variations of the fruit, he says.
The work also showed that levels of smelly sulphur-containing compounds called disulfides that are produced in the fruit increase consequently with the expression of ripening genes.
In a ripe fruit, the expression of one key sulphur-related gene was more than 2,000 times higher than in other parts of the plant. With the ripening factor, the whole fruiting and ripening time can be shortened.
The research could also be used to produce lower sugar varieties.
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