Study sheds light on plants' 'spring switch'

Arabidopsis thaliana (Image: John Innes Centre) Arabidopsis thaliana was the first plant to have its genome sequenced

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Researchers have identified the genetic "switch" that triggers the flowering process in plants as they respond to warmer temperatures.

They found that a gene, known as PIF4, activated the flowering pathway when a certain temperature was achieved.

The team added that the findings could be used in future research to improve crops' resilience to projected changes in the climate.

Details of the study have been published in the journal Nature.

"We have known for hundreds of years that when it gets warmer, plants come into flower," said co-author Philip Wigge from the John Innes Centre, Norwich, UK.

"The question then is... how is it possible that plants are able to control this process with such accuracy and sensitivity."

Dr Wigge said that there were two mechanisms that allowed plants to respond to the arrival of spring: measuring day-length and changes in temperature.

"The switch we discovered is to do with the second one, and helps shed light on how plants know when it is getting warmer," he told BBC News.

"This gene is remarkable because it is only active when it is warm. If you cool the plant down, it has no effect. The gene works in such a way that it is only on in the warm.

"When there are higher temperatures, it activates the target genes and switches on the flowering process."

For their study, the researchers used Arabidopsis thaliana, a small flowering plant native to Europe, Asia and northern parts of Africa.

It was the first plant species to have its genome sequenced, Dr Wigge said, making it a "terrific tool" for molecular biologists.

Out of synch

Dr Wigge explained that plants appeared to use a combination of the two trigger mechanisms but to varying degrees, which affects the characteristics of plants' flowering behaviour.

Kew Gardens (Image: BBC) The study improves the understanding of what triggers plants' responses to warmer temperatures

"Some plants will flower at the same time each spring, whereas other plants will flower earlier if it is warmer. Those are the plants that have an active PIF4 pathway," he said.

"Research carried out by a team in the US has shown that plants that use warmer temperatures to control when they flower are out-competing other plants to a considerable degree.

"In the past 100 years or so, many plants that have just used day-length have become locally extinct.

"Yet plants that have used temperature to control when they flower have increased their range considerably and now much more common.

"That makes a lot of sense because those plants will be able to out-compete other species in a climate change scenario."

Phenological studies have shown that plants are flowering and producing fruit earlier than in the past.

Experts warn that the changes will lead to a breakdown in symbiotic relationships within ecosystems, such as plants' dependence on pollinators.

Protecting crop yields

"We have know for some time that wild plant populations are changing, and they are responding in different ways to changes to the climate," Dr Wigge observed.

"But what we have not understood is the underlying mechanism. So now we know some of the genes that are important in the (flowering) process, we can start to make predictions.

"We can look at ecosystems, and based on whether or not the plants use temperature-based signalling, we can start to make predictions about how ecosystems are likely to change in the future."

The findings can also help crop research, allowing scientists to consider possible ways to ensure yields are not adversely affected by projected climate change.

Dr Wigge said it has been estimated that for every 1C (1.8F) rise in mean global temperatures, crop yields would decline by about 10%.

"Many crops are already been grown near the top of their optimal temperature range," he said.

"Temperature basically has a very large and complex effect on yields. We think that the same process that works in Arabidopsis also works in wheat and barley."

This understanding could allow researchers to modify the plants' responses to temperature changes, either genetically or through breeding programmes.

"Identifying these genes gives you a very powerful tool to modify crops to make them more resilient to climate change," he suggested.

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