Flowering and frost – how plants erase memories of winter – what Lysenko didn’t realise

Plant geneticists from Norwich’s John Innes Centre working with experts from the Chinese Academy of Sciences have uncovered how the memory of cold, so important for flowering, is erased every generation in plants.

The findings are published in Nature in a paper titled ‘Epigenetic reprogramming that prevents transgenerational inheritance of the vernalized state’.

Plants monitor the cold temperature during winter and gradually switch off a gene that acts as a brake to flowering as temperatures decrease.

This gene stays off during spring and summer enabling plants to flower –in other words the gene is ‘epigenetically’ silenced by cold. This process is known as vernalization and is important for the high yielding of winter-sown varieties of many crops including wheat.

Prof Caroline Dean’s research group at the John Innes Centre, a Biotechnology and Biological Sciences Research Council strategically-funded institute, had previously determined how plants ‘remember’ they have experienced winter.

What the team has now unveiled is how this memory is erased between generations, ensuring new seedlings need to feel cold before flowering and create their own memories of cold conditions. Plants actively repress flowering by producing a protein that acts as a brake to flowering.

This gene is progressively switched off during winter and then remains epigenetically silenced through many thousands of cell divisions as the plant develops.

However, at a specific step in seed formation this epigenetic silencing is erased and the brake is re-expressed so the plants growing from the seed have no memories of cold conditions. Professor Dean and her team have now shown that the Arabidopsis thaliana gene called ELF6 is necessary to erase the silencing and get full re-expression of the brake.

This erasure of ‘memories’ between generations contrasts with the widely reported effect of starvation stress in humans and mice, which seems to be inherited through to grandchildren.

Vernalization has long been recognised as an important process in agriculture. In 1930s a young soviet agriculturalist called Trofim Lysenko found that overwintering of peas produced a bumper crop.

A local newspaper picked up on the story of a ‘poor peasant’ and wrote an article entitled “The winter fields” claiming that Lysenko would revolutionise agriculture.

Rising to senior levels in the Soviet leadership Lysenko mandated Russian peasants use his Lamarckian ideas about the inheritance of acquired characteristics for their wheat and potato production. This led to disastrous crop yields and famine.

Professor Dean said: “ Understanding the epigenetic switching mechanisms underlying these environmental responses opens up many possibilities. We can now fully dissect how plants adapt to different environments – so important for breeding new crop varieties that will continue to give high yield as our climate changes”.

The study was supported by BBSRC, the European Research Council, National Basic Research Program of China and the National Natural Science Foundation of China.

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