After a quest lasting more than 70 years, botanists may finally have found what one leading textbook describes as “the Holy Grail of plant biology” – the molecular command that tells a plant it is time to flower.

The discovery may help scientists tailor crops to different latitudes – an especially valuable ability as global warming begins to shift climate zones towards the poles.

Researchers have known since the 1930s that the leaves of plants perceive the seasons by sensing the amount of daylight and, when the time is right, trigger flowering by sending some sort of signal to the shoot tip. But the identity of this so-called “florigen” has remained mysterious.

Now two research teams have independently identified it. Florigen, they say, is the protein produced by a gene called Flowering locus T, or FT. One team, led by George Coupland at the Max Planck Institute for Plant Breeding Research in Cologne, Germany, and Colin Turnbull at Imperial College London in the UK, used genetic trickery to join the FT protein to a green fluorescent protein marker in Arabidopsis, or thale cress.


Green fuse

Onto this marker-enriched plant, the team grafted a mutant stem that lacked the FT gene and so was unable to flower by itself. They observed that the fluorescent FT protein crossed into the mutant stem and triggered flowering. “It’s pretty unambiguous,” says Turnbull.

Another team, led by Ko Shimamoto at the Nara Institute of Science and Technology in Ikoma, Japan, used much the same technique to show the same thing in rice.

Finding the same florigen in two such distantly related species suggests the mechanism is common to all plants, says Jan Zeevaart, a plant biologist at Michigan State University in East Lansing, US.

The new results are not the FT gene’s first turn in the limelight. In recent years, several studies have shown that FT is turned on in leaf tissue at particular day lengths, and that the FT protein acts in the shoot tip to trigger flowering. However, no one knew whether the FT protein or some other molecule was the flowering signal that shuttled from leaf to shoot tip.

Messenger shot

In 2005, researchers in Sweden seemed to settle the question when they announced that messenger RNA from the FT gene was the mobile signal. But this week, the Swedish team formally retracted this claim.

“A guest researcher from China who had been invited to join our team manipulated the data to get false results,” says Ove Nilsson at Umeå University in Sweden. The Chinese researcher, Tao Huang, who is no longer at Umeå University, still stands by his results, says Nilsson.

With the flowering signal now firmly in hand, biotechnologists have the means to tinker with a plant’s flowering time to adapt it to different conditions. For example, farmers at higher latitudes might want to force crops to flower earlier so that they can mature their fruit before the first frost, suggests Brian Ayre, a plant biologist at the University of North Texas in Denton, US.

Reference: Science, doi:10.1126/science.1141752 and doi:10.1126/science.1141753; (retraction) Science, vol 316, p 367