Plants see the light to help beat the big freeze (12/8/2007)

To survive the freezing temperatures of winter, many plants undergo a process termed cold acclimation. In response to the cooler temperatures that presage the onset of winter, plants increase the expression of a large number of genes which lead to the accumulation of proteins and sugars that confer 'antifreeze' properties to cells.

New research at the University of Leicester has revealed that plants also react to another environmental signal, a change in light quality, in order to develop freezing tolerance. The study, led by Dr. Kerry Franklin and Professor Garry Whitelam of the Department of Biology has shown that, at non-acclimating temperatures, a reduction in the ratio of red to far-red wavelengths (R:FR) of light increases the expression of COLD REGULATED (COR) genes and significantly enhances freezing tolerance of the model plant species Arabidopsis thaliana. The ratio of red to far-red light, which is detected by specialized plant photoreceptors called the phytochromes, is highest in direct sunlight and lower in the shade of vegetation or in twilight, which is prolonged at higher latitudes.

Previous work had shown that freezing tolerance is mediated by the CBF family of transcriptional activators and their downstream targets, including the COR genes. The new study shows that exposure to low R:FR light can induce expression of the CBF genes and consequently COR genes, at non-acclimating temperatures, thereby triggering the acquisition of freezing tolerance. The study also showed that expression of CBF genes in response to low R:FR ratio is tightly linked to the plants endogenous timing mechanism, the circadian clock. This would ensure that maximum sensitivity of plants to the low R:FR ratio signal would coincide with the twilight reduction in R:FR ratio when plants are growing in the shorter days of autumn. The work has additionally shown that the linking of CBF regulators to downstream COR genes is uncoupled at higher growth temperatures, a strategy that would prevent the unnecessary accumulation of 'antifreeze' proteins at warmer temperatures. These findings demonstrate how plants can integrate very different environmental signals, in this case light quality and temperature that converge at the level of CBF expression and function, to best prepare for changes in their environment.

This study has recently been published in Nature Genetics (Franklin KA and Whitelam GC (2007). Nat. Genet. 39, 1410-1413) and was funded by the BBSRC and Royal Society.

Described as a 'harbinger of a new era of understanding regarding how plants grow and thrive in a dynamic and complex environment', this work has also been highlighted in the News and Views section of Nature Genetics (Kumar V and Wigge PA (2007) Nat. Gen 39, 1309-1310) and selected as a key article by Faculty of 1000.

This study will additionally be reviewed in the 'Leading Edge: Molecular Biology Select Series' section of the journal Cell ('The Long Twilight Struggle of the Plant Cold War'- out on December 14th).

Note: This story has been adapted from a news release issued by the University of Leicester

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