The strawberry is an octoploid plant: its genome has eight copies of its chromosomes, with four distinct subgenomes. It is far from being a record holder: the blackberry tree has 44 copies of its seven chromosomes.
Like humans, most organisms that reproduce sexually are diploidswhich means they have two copies of chromosomes — one from the mother and one from the father.
However, in plants, things can become very more complicatedand several species, including many agricultural crops, have multiple copies of chromosomes.
For example, cultivated strawberries that you buy in the supermarket (Fragaria × pineapple) they are octoploidswhich means they have eight copies of chromosomes.
But how did they acquire such a complex genome?
The plant species polyploids They obtain their extra chromosomes through two different processes: autopolyploidy and halopolyploidy.
Autopolyploid species simply have multiple copies of their own chromosomes, while allopolyploid species originate from hybridization in which two different sets of chromosomes are combined into a single organism, which often becomes a new species.
Although their genomes persist in modern allopolyploid plantsthe species that contributed their genetic material to these organisms may in the meantime haveer-se extinctwhich makes it particularly difficult to unravel allopolyploid genomes like that of strawberries.
To better understand how the strawberry acquired its eight copies of chromosomes, a team of geneticists at Portland State University turned to retrotransposons long terminal repeats of the genome.
These small genetic elements are repetitive DNA fragments that can be duplicated and inserted into other parts of the genome, explains . By analyzing the patterns of its distribution, researchers are able to obtain a clearer picture of the plant’s evolutionary history.
By applying this new method to strawberries, which was presented in a published in the magazine Horticulture Researchinvestigators were able to determine a few things.
Firstly, the study authors concluded that the strawberry genome is composed of four distinct subgenomes (which makes sense given their octoploidy).
They also concluded that the modern cultivated strawberry went through three events of distinct hybridizations, which occurred approximately 3 to 4, 2 to 3 and 1 to 2 million years ago.
“This work shows how transposable elements can function as evolutionary temporal markers incorporated into plant genomes”, explain the study authors in a statement published in .
“By focusing on when and where these elements expandedwe can reconstruct the history of the genome even when direct ancestral references are missing”, the researchers add.
These new discoveries have important implications for agriculture and plant breeding, including wheat, sugar cane and cotton.
And if you are now wondering where octoploid strawberries rank among polyploid plants… they are a long way from the current known record holder: black mulberry has 44 copies of its seven chromosomeswhich makes it a plant tetratetracontaploide.
