Supergenes play a larger role in evolution than previously thought


Date:
July 8, 2020
Source:
University of British Columbia
Summary:
Large blocks of 'plug and play' genes play a super-sized role in
adaption-and may help fill lingering gaps in Darwin's theories.



FULL STORY ========================================================================== Massive blocks of genes -- inherited together 'plug and play' style --
may play a larger role in evolutionary adaption than previously thought, according to new research in Nature.


========================================================================== Biologists identified 37 of these so-called 'supergenes' in wild sunflower populations, and found they govern the modular transfer of a large range
of traits important for adaptation to local habitats. Those include
seed size, timing of flowering, as well as the ability to withstand environmental stresses such as drought or limited nutrient availability,
among many others.

"We were quite surprised," says University of British Columbia (UBC)
geneticist Marco Todesco. "Cases in which individual supergenes controlled adaptive traits had been reported before, but it wasn't clear if they
were the rule or just a small number of odd exceptions. What found is that supergenes have a pervasive role in adaptation, and can be truly massive."
The largest of the supergenes identified in the study is comprised of
more than 100 million base pairs (larger than many human chromosomes)
and 1,819 genes.

The study could help resolve a question left unanswered by Darwin's theory
of natural selection -- namely, how populations of organisms that live
side-by- side and mate with each other are still able to adapt unique
traits and diverge into separate species.

"Initially, evolutionary biologists believed that geographic isolation
between populations was required for them to differentiate into
ecological races or separate species," says UBC evolutionary biologist
Loren Rieseberg. "But recent research shows that populations that exist
side by side can, and do, differentiate." "The traits that govern such differentiation often appear to be inherited together as supergenes
despite genetic exchange with non-adapted populations that are nearby. In
many cases, plants are able to adapt to a new environment by borrowing
a supergene or two from a related species that is already adapted."


========================================================================== Examples of habitats in which supergenes played a major role in sunflower species adaption include the Texas coastal plain, sand dunes, and coastal barrier islands of the Gulf of Mexico. In the latter case, a 30 million
base pair-long supergene controls a difference in flowering time of
more than two and half months between sunflowers adapted to Texas'
barrier islands and coastal plains. The early-flowering version of the supergene found in the barrier island populations came originally from
the common sunflower.

In some instances, the donor species for the supergene might be
extinct. "What we think could have happened is that a species arrives
in a new habitat, 'steals' adaptive supergenes from a local related
species, and then replaces that species," says Todesco. "We could call
this a 'ghost supergene', the lingering contribution of a species that
no longer exist." Because of their diversity and ability to adapt also
to inhospitable habitats, wild sunflowers have become a model system
for evolutionary studies.

"Genome BC has been investing in this work since 2009," says Lisey
Mascarenhas, Sector Director, Agrifood and Natural Resources at Genome
BC. "A convergence of vision, strategic investments, and scientific
leadership has helped propel innovations in sunflower genomics research
that will have significant implications for food security and continue
to attract global investment to BC." The researchers sequenced the
genomes of more than 1,500 plants from three wild sunflower species:
the common sunflower (Helianthus annuus), prairie sunflower (Helianthus petiolaris), and silverleaf sunflower (Helianthus argophyllus).

They then looked at associations between genetic variants and more
than 80 traits that they monitored throughout the plants' growth, as
well as with the soil and climate of their populations of origin. The
result is the largest and most comprehensive demonstration to date that structural variants - - rearrangements of chromosome structure that are
largely responsible for creating the supergenes in the first place --
play a fundamental and widespread role in adaptation and speciation.

In addition to the supergenes, the study also identified numerous
independent genes that appear to confer resistance to the environmental stresses wild sunflowers face, including drought, heat and low nutrient
stress. These independent genes will be invaluable to sunflower breeders
as they develop cultivars that can tolerate the more extreme growing
conditions predicted under future climate change. From an agricultural standpoint, they offer more flexibility than the supergenes.

"Because they work as a package, introducing a supergene into a cultivated sunflower would mean carrying over both the beneficial and detrimental
traits associated with it,' says Todesco. "While supergenes contain
several genes that could be beneficial in an agricultural setting,
they also contain hundreds of other genes, some of which might not be
so beneficial in a crop. For example, by reducing yield or modifying
the oil content of seeds."

========================================================================== Story Source: Materials provided by University_of_British_Columbia. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Marco Todesco, Gregory L. Owens, Natalia Bercovich, Jean-Se'bastien
Le'gare', Shaghayegh Soudi, Dylan O. Burge, Kaichi Huang,
Katherine L.

Ostevik, Emily B. M. Drummond, Ivana Imerovski, Kathryn Lande,
Mariana A.

Pascual-Robles, Mihir Nanavati, Mojtaba Jahani, Winnie Cheung,
S. Evan Staton, Ste'phane Mun~os, Rasmus Nielsen, Lisa A. Donovan,
John M. Burke, Sam Yeaman, Loren H. Rieseberg. Massive haplotypes
underlie ecotypic differentiation in sunflowers. Nature, 2020;
DOI: 10.1038/s41586-020- 2467-6 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200708125357.htm

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