How do plants remember winter?

Martin Howard is a Professor at the John Innes Centre, one of a small cluster of research institutes in Norwich. In the fourth of our Celebrating Basic Plant Science series, he explains how he uses mathematical modelling to understand how plants remember winter cold and respond to it throughout the year. 

How do plants ‘know’ the correct time to flower? Getting this timing right is vital for reproductive success; flowering in the middle of winter is unlikely to be optimal! Many factors are integrated together to make this critical decision, including the day length.

We have been studying one aspect of this question: How the plant Arabidopsis thaliana perceives and then remembers exposure to winter cold. This fundamental mechanism ensures that flowering doesn’t occur until winter has passed. Interestingly, this memory is quantitative – a longer winter means flowering is faster once it starts (see the image below).  This process is a very nice example of what’s called an epigenetic phenomenon, as the plants store information about winter cold exposure even after the environmental stimulus (cold) has been removed.

So how is this information about cold stored? In Arabidopsis, this is centred on a gene called FLC (Flowering Locus C). When the plant is cold, the FLC gene is turned off. The products of this gene prevent flowering, so turning it off actually stimulates the plant to flower. Over recent years, we have learned a great deal about the operation of FLC and associated genes through genetics and biochemistry, in large part through the work of my experimental collaborator, Caroline Dean. However, despite all this knowledge it was still not clear overall how the epigenetic memory system worked. This was partly due to feedback among the different components, which made arriving at an intuitive understanding a very difficult task. For these reasons, we began to model the dynamics of FLC mathematically in the hope of making sense of these interactions and, we hoped, revealing some underlying simplicity in how the system operated.

Mathematical modelling turned out to be very informative and suggested that FLC gene silencing occurred in an all or nothing fashion inside each cell. (more…)

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