Scientists unearth genetic map of durian, set path for new species
Their day job was cancer research, but a group of scientists from different institutions here had another equally uniting passion.
Gathering together in Chinatown every week to get their fix during the season, the self-confessed durian connoisseurs began to ponder the complexities of the odour and mysterious allure of the king of fruit.
With their curiosity becoming a thorn in the flesh, they began, in their free time, to unravel the durian's DNA.
Three years later, they have a complete genetic map of the fruit - a world first - and some answers to their questions.
"I was curious about the durian genome - what gene causes its pungent smell? How did its spiny husk arise?" said Professor Teh Bin Tean, deputy director (research) of the National Cancer Centre Singapore.
Their research was done on a particular durian variety of Durio zibethinus - the only durian species sold commercially - called Musang King (or Mao Shan Wang). Other durian types, such as the red prawn and the original D24, are all varieties of the same species.
The team found that a durian has some 46,000 genes, double that of humans.
And one type of gene in particular is responsible for its notorious smell - methionine gamma-lyase (MGL), which regulates odour compounds called volatile sulphur compounds (VSCs), which can smell like rotten eggs or onions.
Unlike other plants that typically have just one or two MGL copies, durians have four, which means their production of VSC is "turbocharged", and that explains why they are so pungent, said study co-leader Patrick Tan, who is from Duke-NUS Medical School.
A paper on their study was published online in the prestigious journal Nature Genetics yesterday.
The research was carried out using advanced sequencing technology that is ideal for studying plant genomes, and which became mainstream only a few years ago.
But while technology had a role to play in kick-starting the research project, it was the love of the fruit that ultimately made it possible, the team said.
The $500,000 project was funded by "fellow durian lovers", who wished to be anonymous.
It was, at times, a rough ride.
The scientists had many bumpy drives to durian plantations in Johor Baru where they begged farmers to let them buy unripe durians for their research, said Mr Cedric Ng, senior research associate at NCCS. Unripe fruit were needed to study how the level of MGL changed as the fruit developed.
"It is taboo to pluck off unripe fruits because they think their tree will die after," he said.
"But it has been an exhilarating journey."
The team had to extract the DNA from the durian plant multiple times to be sequenced.
The durian genome data has been donated to the National Parks Board. By unravelling the durian genome, the group has taken the first step towards identifying genes involved in disease resistance, flavour, drought tolerance, and other traits.
The team hopes that its effort will pave the way for researchers to create new durian species that are drought-resistant, or low-sugar varieties suitable for diabetics, for instance.
There are 30 other durian species in nature, of which 11 are edible. Some are endangered.
Said Dr Nigel Taylor, group director of the Singapore Botanic Gardens: "Understanding the genome of a species can enable you to understand how to conserve it, and also its relatives."