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

賈森·戴利/文　陳先宇/譯

The DNA of the durian， it turns out， is very complex and optimized for producing a wretched stench1. 研究發現，榴蓮的DNA異常復雜，而且為了能夠產生惡臭而進行了優化。

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.”

榴蓮這種水果最讓人琢磨不透。它個頭大得像甜瓜或者橄欖球，渾身帶刺，外殼氣味實在難聞，以至于新加坡禁止榴蓮出現在公共交通工具和公共場所里。美食作家理查德·斯特林曾將榴蓮比作混合了“松脂、洋蔥，再用一只運動襪點綴”的豬糞。然而，榴蓮雖然氣味濃烈，但類似蛋奶沙司的果肉細膩可口，為其圈粉無數——他們形容這種烈性水果“外表像地獄，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.

愛也好，恨也罷，與榴蓮邂逅的人大多對其印象深刻。榴蓮號稱“水果之王”，為揭示其臭味之源，研究人員對其基因組進行了檢測，研究結果發表于《自然·遺傳學》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.

榴蓮屬下約有30個物種，其中最常見的榴蓮約有200個品種是面向市場培育的。榴蓮其實是亞洲的重要經濟作物，僅中國每年就進口價值高達6億美元的榴蓮。因此，稍微了解一下榴蓮的基因組，對培育榴蓮新品種和預防榴蓮病害都非常重要。

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.

貓山王是最美味、最受歡迎的榴蓮栽培品種之一，新加坡國立癌癥中心的研究人員對貓山王榴蓮的基因組進行了測序。他們發現，貓山王是一個極其復雜的品種，有近4.6萬個基因，大約是人類基因數量的兩倍。同樣有趣的是，他們發現這個散發臭味的物種與另一種人們喜愛的植物——用于制作巧克力的可可——在進化過程中有著共同的祖先。

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，據肯德拉·皮埃爾-路易斯在《大眾科學》雜志上發表文章稱，榴蓮的祖先自6500萬年前與可可分離后，發生了根本性改變。榴蓮基因組經歷了重復事件，也就是說榴蓮復制了其祖先可可的基因組，然后將其融入自己的DNA。如此一來，榴蓮能夠繼續發揮原始基因組賦予其的基本功能，復制而來的另一組基因同時開始改進和突變，比如進化出長刺的外殼和難聞的氣味。

“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.

研究論文作者帕特里克·陳（音譯）是杜克-新加坡國立大學醫學院的研究員。他告訴皮埃爾-路易斯：“這差不多就像你克隆了你自己。你讓其中一個你去做諸如家務活、打掃衛生之類的事，另一個你就可以繼續做其他各種各樣的事。”

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.

研究人員識別出了榴蓮進化出來用于散發臭味的一個基因。他們認為榴蓮之所以要散發臭味，是為了吸引猩猩和人類等靈長類動物來傳播自己的種子。研究人員發現了一種名為甲硫氨酸γ-裂解酶的基因，可以調節揮發性硫化物的產生，而這類硫化物相當臭。

“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.”

“我們發現這種基因只在果肉中高度表達，而在葉、莖、根中并沒有。”研究論文合著者鄭敏展向澳大利亞廣播公司的記者蓋內爾·沃伊勒透露，“這給了我們第一條重要線索，說明它是使榴蓮產生強烈刺鼻氣味的關鍵基因?！?/p>

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.

沃伊勒報道稱，硫化物的生成在榴蓮中得到了強化。榴蓮近親（如可可）只有1個甲硫氨酸γ-裂解酶拷貝，而榴蓮有4個，這說明榴蓮為了能產生吸引靈長類動物的臭味而進行了優化——特別是因為這些基因只在果實成熟后才發揮作用。

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.

這只是榴蓮臭味配方中的一個成分。正如約瑟夫·斯特龍伯格在2012年所述，研究人員發現榴蓮的臭味來自50種化合物，其中4種是當時科學界的新發現。2017年發表的另一項研究發現，榴蓮的氣味主要來自兩種化合物：一種聞起來像水果；另一種聞起來像洋蔥。

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.

鄭敏展告訴沃伊勒，基因組研究還可能引發對榴蓮的遺傳修飾，從而使科學家能夠消除臭味基因。然而，并非所有人都樂于接受這種改變，畢竟食用榴蓮的樂趣大半在于邊忍受惡臭，邊狼吞虎咽地享用口感細膩的果肉。

（譯者為“《英語世界》杯”翻譯大賽獲獎者；單位：中國巨石股份有限公司）

1 stench臭味。

2 rank難聞的。? 3 turbocharge渦輪增壓，增強。

4遺傳修飾是通過分子生物學技術對生物體的基因組進行改造的技術。