Why plant ‘clones’ aren’t clones

Plant clones are not often identical to the donor plant – a fact that has puzzled researchers until now.

A team from the University of Oxford’s department of plant sciences has shown why clonal plants are not always identical – it’s down to mutations, but not those inherited from the parent plant.

“Anyone who has ever taken a cutting from a parent plant and then grown a new plant from this tiny piece is actually harnessing the ability such organisms have to regenerate themselves,” said Professor Nicholas Harberd.

“But sometimes regenerated plants are not identical, even if they come from the same parent. Our work reveals a cause of that visible variation.”

Using whole genome sequencing, the team analysed the clones of the small flowering plant thale cress. They revealed that the genomes of regenerant plants carry relatively high frequencies of new DNA sequence mutations not present in the parent plant.

“Where these new mutations actually come from is still a mystery,” said Harberd. “They may arise during the regeneration process itself or during cell divisions in the donor plant that gave rise to the root cells from which the regenerant plants are created.

“What we can say is that Nature has safely been what you might call a ‘cloning’ process in plants for millions of years, and that there must be some good evolutionary reasons why these mutations are introduced.”

The results suggest that variation in cloned plants may have different underlying causes from that of variation in clones of animals, where it is believes that the effect of environmental factors on how animal genes are is expressed is more important and no similar high frequencies of mutations have been observed.

“Whilst our results highlight that cloned plants and animals are very different they may give us insights into how both bacterial and cancer cells replicate themselves, and how mutations arise during these processed which, ultimately, have an impact on human health,” said Harberd.