Sniff Out the Genes Behind the Smell of Durian探究榴莲臭味的基因之源

贾森·戴利/文　陈先宇/译

The DNA of the durian， it turns out， is very complex and optimized for producing a wretched stench1. 研究发现，榴莲的DNA异常复杂，而且为了能够产生恶臭而进行了优化。

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.”

榴蓮这种水果最让人琢磨不透。它个头大得像甜瓜或者橄榄球，浑身带刺，外壳气味实在难闻，以至于新加坡禁止榴莲出现在公共交通工具和公共场所里。美食作家理查德·斯特林曾将榴莲比作混合了“松脂、洋葱，再用一只运动袜点缀”的猪粪。然而，榴莲虽然气味浓烈，但类似蛋奶沙司的果肉细腻可口，为其圈粉无数——他们形容这种烈性水果“外表像地狱，里面是天堂”。

Whatever its love or hate， most who have encountered durian have a strong opinion about it. 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.

爱也好，恨也罢，与榴莲邂逅的人大多对其印象深刻。榴莲号称“水果之王”，为揭示其臭味之源，研究人员对其基因组进行了检测，研究结果发表于《自然·遗传学》期刊。

There are about 30 species in the Durio genus， and the most common species， Durio zibethinus， has about 200 varieties that are bred for the market. In fact， its 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.

榴莲属下约有30个物种，其中最常见的榴莲约有200个品种是面向市场培育的。榴莲其实是亚洲的重要经济作物，仅中国每年就进口价值高达6亿美元的榴莲。因此，稍微了解一下榴莲的基因组，对培育榴莲新品种和预防榴莲病害都非常重要。

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.

猫山王是最美味、最受欢迎的榴莲栽培品种之一，新加坡国立癌症中心的研究人员对猫山王榴莲的基因组进行了测序。他们发现，猫山王是一个极其复杂的品种，有近4.6万个基因，大约是人类基因数量的两倍。同样有趣的是，他们发现这个散发臭味的物种与另一种人们喜爱的植物——用于制作巧克力的可可——在进化过程中有着共同的祖先。

But， reports Kendra Pierre-Louis at Popular Science， durians 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 rank2 odor.

然而，据肯德拉·皮埃尔-路易斯在《大众科学》杂志上发表文章称，榴莲的祖先自6500万年前与可可分离后，发生了根本性改变。榴莲基因组经历了重复事件，也就是说榴莲复制了其祖先可可的基因组，然后将其融入自己的DNA。如此一来，榴莲能够继续发挥原始基因组赋予其的基本功能，复制而来的另一组基因同时开始改进和突变，比如进化出长刺的外壳和难闻的气味。

“Its 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 Singapores Duke-NUS Medical School， tells Pierre-Louis.

研究论文作者帕特里克·陈（音译）是杜克-新加坡国立大学医学院的研究员。他告诉皮埃尔-路易斯：“这差不多就像你克隆了你自己。你让其中一个你去做诸如家务活、打扫卫生之类的事，另一个你就可以继续做其他各种各样的事。”

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.

研究人员识别出了榴莲进化出来用于散发臭味的一个基因。他们认为榴莲之所以要散发臭味，是为了吸引猩猩和人类等灵长类动物来传播自己的种子。研究人员发现了一种名为甲硫氨酸γ-裂解酶的基因，可以调节挥发性硫化物的产生，而这类硫化物相当臭。

“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.”

“我们发现这种基因只在果肉中高度表达，而在叶、茎、根中并没有。”研究论文合著者郑敏展向澳大利亚广播公司的记者盖内尔·沃伊勒透露，“这给了我们第一条重要线索，说明它是使榴莲产生强烈刺鼻气味的关键基因。”

Weule reports that the production of these sulfur compounds is turbocharged3 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.

沃伊勒报道称，硫化物的生成在榴莲中得到了强化。榴莲近亲（如可可）只有1个甲硫氨酸γ-裂解酶拷贝，而榴莲有4个，这说明榴莲为了能产生吸引灵长类动物的臭味而进行了优化——特别是因为这些基因只在果实成熟后才发挥作用。

Thats just one element of durians odorific formula. As Joseph Stromberg wrote in 2012， researchers discovered that the fruits odor comes from 50 different compounds， including four that were new to science at the time. Another study published in 2017 found that two main compounds， one that smells fruity and one that smells like onions， give the durian most of its smell.

這只是榴莲臭味配方中的一个成分。正如约瑟夫·斯特龙伯格在2012年所述，研究人员发现榴莲的臭味来自50种化合物，其中4种是当时科学界的新发现。2017年发表的另一项研究发现，榴莲的气味主要来自两种化合物：一种闻起来像水果；另一种闻起来像洋葱。

The genome research could also lead to genetic modification4 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.

郑敏展告诉沃伊勒，基因组研究还可能引发对榴莲的遗传修饰，从而使科学家能够消除臭味基因。然而，并非所有人都乐于接受这种改变，毕竟食用榴莲的乐趣大半在于边忍受恶臭，边狼吞虎咽地享用口感细腻的果肉。

（译者为“《英语世界》杯”翻译大赛获奖者；单位：中国巨石股份有限公司）

1 stench臭味。

2 rank难闻的。  3 turbocharge涡轮增压，增强。

4遗传修饰是通过分子生物学技术对生物体的基因组进行改造的技术。