The durian is a most confounding fruit. The outer layer of these large spiky melon-like footballs smell so bad that it is banned from public transportation and public spaces in Singapore. Food writer Richard Sterling has described it as pig poop mixed with “turpentine and onions, garnished with a gym sock.” The taste of the custardy inside, however, has garnered the potent fruit millions of fans, describing it as “hell on the outside and heaven on the inside.”
Whatever it's love or hate, most who have encountered durian have a strong opinion about it. Now, reports Agence France-Presse, in an effort to unravel its stinky goodness researchers examined the genome of this “king of fruits.” They published their results in the journal Nature Genetics.
There are about 30 species in the Durian family, and the most common species, Durio zibethinus, has about 200 varieties that are bred for the market, according to the AFP. In fact, it’s an important cash crop in Asia—China alone imports $600 million worth of the fruit each year. So understanding a little about its genome is important to breeding new varieties and safeguarding the species from disease.
Researchers at the National Cancer Centre in Singapore sequenced the genome of a durian variety called Musang King, one of the most delicate and popular cultivars. What they found is an extremely complex plant, with nearly 46,000 genes—about twice the number found in humans. Equally interesting, they found the stinky species shares an evolutionary ancestor with another favorite plant, cacao, which is used to make chocolate.
But, reports Kendra Pierre-Louis at Popular Science, durian’s ancestors went through some radical changes once it split from cacao 65 million years ago. The genome of durian underwent a duplication event. This means that it copied the genome of its cacao ancestor and incorporated it into its DNA. That allowed the plant to continue on with its essential functions in this original set of genes, while another set began changing and mutating—such as its development of thorny skin and rank odor.
“It’s almost like you cloned yourself, and you have one copy of yourself go and do the housework and cleaning and so forth so the other one can go on and do all sorts of different things,” study author Patrick Tan, researcher at Singapore’s Dune-NUS Medical School, tells Pierre-Louis.
Researchers identified one of the genes the durian developed to produce its odor, which they believe is produced to attract primates, like orangutans—and humans—who disperse the seeds. The researchers found a class of genes called methionine γ-lyase (MGLs) that regulate the production of volatile sulfur compounds, which are quite stinky.
“We found that this gene is highly expressed only in the fruit — the pulp — but not in the leaves or the stem or the roots,” co-author Bin Tean Teh tells Genelle Weule at the Australian Broadcasting Corporation. “This gave us the first clue that this is a key gene that results in the strong, pungent smell of durian.”
Weule reports that the production of these sulfur compounds is turbocharged in durians. While close cousins like cacao only have one copy of the gene, durian has four versions of the stink gene, meaning the fruit is optimized for producing a primate-enticing funk—especially since those genes are only active when the fruit is ripe.
That’s just one element of durian’s odorific formula. As Joseph Stromberg wrote for Smithsonian.com in 2012, researchers discovered that the fruit’s odor comes from 50 different compounds, including four that were new to science at the time. Another study published earlier this year found that two main compounds, one that smells fruity and one that smells like onions, give the durian most of its smell.
The genome research could also lead to genetic modification of the fruit, allowing scientists to knock out the stink gene, Teh tells Weule. But not all would welcome the change; half the fun of durian is enduring the stench while chowing down on its creamy center.