The role of genetics in white clover's global takeover

Both an important forage crop and an invasive species, white clover is of economic significance in Aotearoa New Zealand. Recent research has deepened our understanding of how clover adapts and succeeds in new environments by collecting the largest genetic dataset for an invasive plant to date.

An international team, led by researchers from University of Louisiana, Lafayette; Monash University and University of Toronto, Mississauga, and including Te Whare Wānaka o Aoraki Lincoln University Senior Lecturer Dr William Godsoe, share their work in the article Haploblocks contribute to parallel climate adaptation following global invasion of a cosmopolitan plant published in Nature Ecology and Evolution. The research found that many of the genes that help white clover (Trifolium repens) adapt to new climates are closely linked and often inherited together.

"One of the roles of genetic variation is to help plants adapt. In white clover, some of its genes are organised into 'folders'. This organisation makes it easier to find what is needed when the plants face a new environmental challenge," explains Dr Godsoe.  

To contribute to samples collected internationally, Dr Godsoe gathered specimens from locations in Canterbury, New Zealand, which added rich context to the international study. He says this is of particular interest as New Zealand is remote from many major continents and grows its distinct cultivars of white clover.

Originally from Europe and western Asia, white clover has rapidly spread across the world as a forage and rotational crop and invaded surrounding natural areas. Researchers sequenced genomes of 2,660 individuals from 13 native white clover populations, 39 populations across five introduced ranges and 12 widely used cultivars. Transcontinental field trials were conducted using a diverse set of clover varieties to determine the local advantages conferred by different areas of the genome. Through this data collection and analysis, researchers now understand how the plant’s genetics support adaptation.

“Taking this international approach was significant”, says Dr Godsoe. “When you’re looking at evolution, many plants and animals are sensitive to their environment. You might know what’s happening in your backyard, but there’s uncertainty about whether backyards in other countries are experiencing the same.  

“White clover has lots of raw material and high genetic diversity to help it evolve and adapt to different climates. We now have this large pool of data that shows the patterns of genetic diversity in white clover and how they present in different environments. And that’s incredibly helpful to researchers who are looking at patterns of evolution in other invasive species to better understand why some establish easily and others fail to spread.”

The research now confirms white clover’s genetic make-up, highlighting that five large-effect structural variants – or groups of genes that are located close to one another in the genome and inherited together – found on three chromosomes, within both native and introduced varieties, are associated with rapid adaptation to climate in introduced regions. The signatures in each group of genes were present in climates similar regardless of the location worldwide.

"As genetic cultivars of white clover are economically important in New Zealand, it is great to have a wealth of information on how clover adapts to local conditions, providing a road map of the genes that help clover evolve in sites all over the world," says Dr Godsoe.

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