In the vast and vibrant world of plants, the sunflower family stands out for its sheer diversity, including beloved blossoms like asters, daisies, and economically significant crops such as lettuce and artichokes.
A groundbreaking study led by a team from Penn State has cast new light on this family’s evolutionary journey, revealing the intricate dance of flower symmetry evolution through a phenomenon known as convergent evolution.
This discovery not only deepens our understanding of plant evolution but also holds promise for the future of plant breeding.
Convergent evolution is a process where different species evolve similar traits independently of each other, often in response to similar environmental challenges or lifestyle needs. The classic examples include the wings of birds and bats, which serve the same function but evolved separately.
Within the sunflower family, this concept plays out in the realm of flower symmetry—the way a flower’s parts are arranged and can be divided into equal halves.
The study focused on the sunflower head, which is not a single flower but a composite of many smaller flowers. While the overall head exhibits radial symmetry, meaning it can be divided into equal halves in multiple ways, the individual flowers within it can vary in symmetry.
Bilateral symmetry, where a flower can be divided into mirror-image halves along only one line, was found to have evolved and disappeared multiple times across different sunflower species.
This surprising revelation points to a dynamic evolutionary history driven by genetic changes, particularly in the CYC2 gene, which regulates flower development.
To unravel the complex family tree of the sunflower family, the research team utilized a combination of genetic data sources, including transcriptomes and low-coverage genome sequences.
Transcriptomes, which capture the genes expressed by a species, provide a rich source of genetic information but are challenging and expensive to obtain.
Low-coverage genome sequences, on the other hand, offer a more accessible yet informative snapshot of a species’ DNA, even from dried plant samples.
This innovative approach enabled the researchers to include a vast array of species in their analysis, greatly enhancing the resolution of the sunflower family tree.
By analyzing the genetic data of 706 species, spanning 16 subfamilies and numerous tribes and genera, the team was able to identify the finer branches and twigs of the family tree.
This detailed view allowed them to pinpoint where and when specific traits, like flower symmetry, evolved. The study’s findings underscore that bilateral symmetry in flowers emerged multiple times independently, highlighting the diverse evolutionary paths within the sunflower family.
Further analysis of the CYC2 gene revealed its crucial role in the evolution of flower symmetry. The gene’s expression patterns in species with bilaterally symmetric flowers suggest that changes in how this gene is activated are likely behind the repeated emergence of this trait.
This insight into the molecular underpinnings of flower development opens new avenues for understanding how plants evolve and adapt.
The sunflower family, with over 28,000 species, is a testament to the incredible diversity of life and the complex evolutionary processes that shape it.
This research not only sheds light on the evolutionary history of one of the largest families of flowering plants but also offers valuable knowledge that could inform the selective breeding of plants.
By understanding the genetic relationships and traits within this family, scientists and breeders can identify desirable characteristics in wild species that could be transferred to cultivated ones, enhancing agricultural and horticultural practices for future generations.
The research findings can be found in Plant Communications.
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