Meadow flowers unlocking evolution: Scientists decode Y chromosome DNA

What does the Silene latifolia plant have in common with humans? Separate sexes. One white campion growing between fields might be male, while just a few steps away, another will be female. Scientists from the Institute of Experimental Botany of the CAS and the Institute of Biophysics of the CAS, along with international colleagues, have cracked the DNA of the Y chromosome responsible for shaping the stamens and producing pollen in the male flowers of Silene latifolia. They even uncovered how this plant developed what is known as dioecy – the evolution of distinct unisexual individuals in a species. These insights into the evolution of sexual reproduction in plants may also shed light on human biology. The research was published in Science.

You’ll often be able to spot Silene latifolia, commonly known as white campion, on Czech meadows and along hedgerows. The flower is often picked on strolls to complement a bouquet. While its delicate white petals are pretty, it’s the velvety, sometimes purplish, stems that really catch the eye, along with the peculiar balloon-like structures beneath some of its flowers. These inflated calyxes, with their seed capsules, belong to female plants, while the slender, cylindrical calyxes on other stems carry only male flowers with stamens and pollen.

Silene latifolia is a dioecious plant species, meaning it has evolved separate male and female sexes, with individual plants bearing exclusively male or female reproductive organs. Other plants like willows, hops, and hemp also exhibit dioecy. Gardeners and orchardists are familiar with this phenomenon as well – for instance, anyone growing sea buckthorn for its vitamin-rich berries needs to plant both a male and a female shrub. The same goes for the medicinal ginkgo tree.

A male Silene latifolia plant.

Similarly, white campion requires both male and female plants to reproduce. While it doesn’t offer vitamin-packed fruits or culinary uses, it holds something perhaps even more valuable: insight. “Studying Silene latifolia helps us answer fundamental questions about the fate of our genomes – and, by extension, our own fate,” explains Helena Štorchová from the Institute of Experimental Botany of the CAS, who leads the Laboratory of Plant Reproduction there.

Silene latifolia has fascinated scientists for centuries. It is no coincidence that Gregor Johann Mendel, the father of genetics, chose this plant as a model for studying the fundamental principles behind the development of sex chromosomes and the determination of sex.

Following the trail of the male genome
But how could a simple meadow flower reveal anything about the human species? Silene latifolia has a sex-determination system similar to humans. Male plants carry X and Y chromosomes, while female plants have two X chromosomes. It is the Y chromosome’s genetic information in Silene latifolia that an international team of scientists from eight European countries, the USA, and Chile took a deep dive into.

Chromosomes of male Silene latifolia plants, including the massive Y sex chromosome.

Decoding the genetic information was no easy feat. The Y chromosome DNA in Silene contains numerous repetitive sequences, which makes analyzing it tricky. To complicate matters further, it’s enormous – comprising over 500 million base pairs of genetic information. That’s about four times the size of the genome of Arabidopsis thaliana (a popular model organism) and nearly one-sixth the size of the entire human genome, which consists of 23 chromosomes.

“Unlike the human Y chromosome, Silene’s Y chromosome is evolutionarily young. It began forming around 11 million years ago. Over time, recombination with the X chromosome – where the two chromosomes pair up and exchange corresponding regions – became increasingly restricted. This led to the accumulation of repetitive DNA sequences, causing the Y chromosome to grow to its current massive size,” explains Roman Hobza from the Institute of Biophysics of the CAS.

A vital message from an inconspicuous plant
To achieve a detailed sequence of Silene’s Y chromosome – in simplified terms, the order of the “genetic letters” encoding hereditary information – scientists employed a combination of cutting-edge DNA sequencing techniques. They also managed to identify genes that might be responsible for the primary functions of the Y chromosome: suppressing the development of female reproductive structures (carpels) and promoting the formation of male stamens and pollen production.

The flowers of Silene latifolia – female on the left, male on the right.

In addition to Silene latifolia, researchers analyzed the genomes of two closely related species – Silene vulgaris and Silene conica – which do not have separate sexes. Comparing these genomes revealed the complex origins of Silene’s sex chromosomes, which formed from fragments of other chromosomes.

Czech researchers played a significant role in the project. The team from the Institute of Biophysics of the CAS, led by Roman Hobza, contributed to analyzing Silene’s sex chromosomes. Meanwhile, two teams from the Institute of Experimental Botany of the CAS, headed by Helena Štorchová and Hana Šimková, worked on assembling the genome of Silene vulgaris.

“Even seemingly unremarkable plants can offer key insights into fundamental biological processes. Silene latifolia is becoming one of the essential model species for understanding the evolution of reproduction,” Hobza concludes.

Written and prepared by: Jana Bečvářová, External Relations Division, CAO of the CAS, drawing on the CAS press release
Translated by: Tereza Novická, External Relations Division, CAO of the CAS
Photo: Archives of the Institute of Experimental Botany of the CAS and the Institute of Biophysics of the CAS

 The text is released for use under the Creative Commons license.

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