Genetic link to durian’s stink

It’s fair to say that durian – a large, spiky fruit common in Thailand, Indonesia and Malaysia – evokes a mixed reaction.

It is a major cash crop, and while its millions of devotees call it the king of fruit, it’s critics are not so kind. Typical is US chef and food writer Anthony Bourdain, who wrote that “it smelled like you’d buried somebody holding a big wheel of Stilton in his arms, then dug him up a few weeks later.”

Indeed, the smell of durian is so strong, a rich blend of sulfur, onion and (some add) old sock, that it is banned on many forms of public transport and in most major hotel chains.

Despite the fact that more than 250,000 hectares are given over to durian cultivation, until recently very little was known about the genetic basis for its shape, texture, taste and smell.

Now, however, a team, led by Bin Tean Teh from Thorn Biosystems in Singapore has succeeded in sequencing the durian genome for the first time, down to single-molecule resolution.

The scientists used a popular cultivar of the plant (Durio zibethinus) in an attempt to unlock the genetic mechanisms that cause the ripened fruit to give off – as they diplomatically describe it – “a complex suite of odour-active compounds including sulfur volatiles, esters, alcohols, and acids”.

The team found the plant had undergone a whole genome replication event, which probably occurred before it split with its distant relatives, cotton and cacao.

Such duplication events, the scientists note, are often strong drivers of evolution, in part because they create a lot of newly redundant alleles that can then develop novel functions. This appears to have happened with durian, where there has been a boost to genes linked to the presence of sulfur compounds, particularly in the fruit of the plant.

The research also found a genetic link for increased production of ethylene – a sweet-smelling compound that lends durian’s odour its “oniony” dimension and is a key olfactory indicator of ripeness.

“It is possible that linking odour and ripening may provide an evolutionary advantage for durian in facilitating fruit dispersal,” the researchers write, suggesting that sweet smells are prime tools used by some other plant species that depend on large animals, such as primates, to distribute their seeds.

Bin Tean Teh and colleagues conclude that the fully sequenced genome will be useful in research to better manage the hundreds of D. zibethinus cultivars that are grown through southeast Asia.

The data will also be useful in studying the 30 species that share the durian’s genus, many of which don’t produce fruit, and some of which are endangered.

The research was published in the journal Nature Genetics.