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How plants erase the memory of winter

A study by the CBGP researcher Pedro Crevillén published in Nature characterizes how the epigenetic memory of vernalization is erased at the molecular level.

Plants decide when to flower in response to environmental cues through a complex gene regulatory network. In some species, flowering requires the plant to be exposed to prolonged periods of low temperatures, like winter cold. This process is known as vernalization and it is crucial for growing several crops such as wheat, barley and all the Brassicaceae family (rapeseed, mustard, cabbage, broccoli, etc.).

Vernalized plants are able to remember winter by keeping silenced a floral repressor during subsequent growth at warm temperatures in the spring. This "epigenetic memory" is erased and the floral repressor is reactivated during seed formation. This process ensures that the next generation of plants maintain a vernalization requirement to flower. However, the genetic mechanisms which control this resetting process remained unknown until recently. A study by Pedro Crevillén from CBGP working with colleagues from John Innes Centre (Norwich, UK) and The Chinese Academy of Sciences published in “Nature” has discovered how this memory of winter is erased between generations.

Epigenetic marks are heritable chemical modifications that regulate genome function without altering the DNA sequence. For example, twins share the same DNA sequence, but a fine analysis of their genomes reveal that they are marked differently by epigenetic modifications accumulated throughout their lives. This fact explains, to some extent, the observed differences between identical twins.

In the model plant Arabidopsis thaliana, there is gene called FLC that acts as a “floral brake”. This floral brake is silenced during the winter. After the cold, this gene remains silenced by epigenetic mechanisms in the absence of cold allowing the plants to bloom in spring. Later, this gene is reactivated in the seeds and the new plants require to overwinter (vernalize) to flower again.

 

 

 

Vernalization is a process of great importance for a number of crops. In the case of wheat, different varieties must be sown in different seasons depending on their vernalization requirement. In recent years, due to the effects of climate change, winters are less cold than they use to be. This reduces crops yield because some plants are unable to flower at the right time. Dr. Crevillén said that the results of this study, led by Prof. Caroline Dean from John Innes Centre, may allow us to get more productive plants varieties in the current environmental conditions.

The study, published in Nature entitled "Epigenetic reprogramming that prevents transgenerational inheritance of the vernalized state", characterized how the epigenetic memory of vernalization is erased at the molecular level. The authors also show that ELF6 gene is required for this epigenetic reprogramming. This research work was made possible by the isolation of a mutant ELF6 gene which made the plant able to “rememeber” vernalization across generations. This mutant is one of the few examples of transgenerational epigenetic inheritance that has been studied in plants. "This work recalls the ideas of Lysenko, the Soviet botanist who wrongly claimed that the progeny of vernalized wheat would flower increasing their production," said Dr. Crevillén. "However, he was wrong and we now know that vernalization is needed in every generation for plants to flower."

Epigenetic changes also affect humans.

Scientists have recently discovered that epigenetic transgenerational inheritance affects not only plants but also animals and therefore humans. Initially, it was thought that epigenetic changes could only be inherited from cell to cell within the same organism, but not from one generation to another, ie from parents to children. However, numerous studies are suggesting that a small part of this epigenetic information is not erased and is transmitted to the offspring. For example, malnutrition in expectant mothers causes epigenetic changes that affect not only their children, but may have consequences for their grandchildren growth. This is a hot topic nowadays which has caught the international community attention, although more research is still needed. The next step to complete the study, according to first author Dr. Crevillén, would be to deeper into the mechanisms of how plants regulate flowering in response to changes in ambient temperature. "These studies become more important today if we want to prevent the adverse effects of climate change, because we know that increasing temperatures cause epigenetic changes that regulate flowering time", says Crevillén, who has recently been awarded with a Ramón y Cajal contract to continue his research.

Epigenetic reprogramming that prevents transgenerational inheritance of the vernalized state - DOI:10.1038/nature13722

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