Gene 'alarm' makes plants flower

Many flowers need a cold spell before they can bloom in Spring

Many plants have a genetic alarm clock to tell them when to wake from their winter slumber and bloom in spring, scientists have discovered.

The question of how plants know when it is time for them to flower has perplexed scientists for generations.

But a team of British and US researchers has uncovered clues that may help to explain the conundrum and help to increase crop productivity.

Details of the research are published in the scientific journal Nature.

In the first of two studies published in the journal, researchers uncovered clues to why certain plants need a cold spell to stimulate flowering.

Although several genes linked to flowering have already been identified, researchers at the University of Wisconsin-Madison have found another, called VIN3.

This plant gene blocks the expression of another known as FLC. The FLC gene encodes a protein that prevents flowering.

"It is part of the system that measures the duration of cold," said Professor Richard Amasino, a biochemist at the University of Wisconsin-Madison.

The cold spell needed by many plants to stimulate flowering is called vernalisation.

In bloom

Certain plants grow in the autumn but shut down in the winter and need to make sure they are not tricked into flowering too soon during an early warm spell.

Flowering time can have a big effect on crop yields Professor Caroline Dean, John Innes Centre

"VIN3 is a piece of the system designed to recognise that it has been a complete winter," Professor Amasino said.

Amasino and colleague Sibum Sung, who pinpointed VIN3, said it went into action only after the plant had been exposed to the winter cold.

They identified the gene in a variety of Arabidopsis thaliana, a common weed that takes two seasons to bloom.

Mutant plants without VIN3 did not bloom at all. Professor Amasino and his team explained that the VIN3 protein is needed to alter proteins called histones bound to the FLC gene.

In the autumn, histones are modified so FLC is highly expressed. But in the spring, after vernalisation, they silence the FLC gene and switch the plant into a flowering state.

Plant 'memory'

In a second study in the journal, scientists at the John Innes Centre in Norwich, England also studied Arabidopsis to identify chemical changes in plants that help them "remember" they have gone through a cold period.

In previous research they showed that two genes, VRN1 and VRN2, were involved in flowering.

In the latest study, they discovered that the genes caused chemical changes in a histone called H3 that makes the plants remember they have had a long period of cold to stimulate them to flower in spring.

"In the depths of a British winter we are all looking forward to the coming of spring when we can forget the cold.

"But many plants will be remembering the winter cold to ensure that, come spring, they flower at the right time," said Professor Caroline Dean, leader of the research team.

"Understanding this process is of tremendous scientific importance but it is also of practical interest as flowering time can have a big effect on crop yields," she added.