Most humans are diploid, meaning we have two sets of chromosomes—one from each parent. However, this isn’t the case for all species, particularly among plants.
Take strawberries, for example; they actually have eight sets of chromosomes, explains Yves Van de Peer, a plant biologist at Ghent University in Belgium.
This occurrence, known as polyploidy, results when an organism possesses more than two sets of chromosomes within its cells—essentially a complete duplication of its genome. It seems that this trait allows certain plant species to endure severe environmental stress, such as climate change.
Biologists weren’t initially convinced that polyploidy was beneficial. After all, having double the chromosomes could hinder a species’ chance of survival, potentially leading to extinction. Interestingly, it’s quite common today, particularly in plants, which raises a question posed by Van de Peer: the polyploidy paradox—why do so many plants exhibit a trait that might make them evolutionarily weaker?
In recent research published in the journal Cell, Van de Peer and his team propose a solution to this riddle. They analyzed historical genome duplication instances across several hundred plant species and found these events often coincided with periods of turmoil over the last 150 million years—times marked by significant climate changes or mass extinctions. So, polyploidy may have distinct advantages when the environment gets tough.
Van de Peer feels he may have unraveled this long-standing puzzle. With a chuckle, he notes, “I think I can retire now since this is the culmination of 25 years of work.”
Clusters in time
Van de Peer likens polyploidy to a large-scale mutational event. He explains, “Sometimes things go awry, resulting in a new cell that contains double the DNA of a typical plant cell.”
Although these species may thrive for a spell, this complete genome duplication isn’t without its complications. Extra chromosomes can complicate cell division, increasing the likelihood of errors and mutations. This could allow other plants with lighter genetic loads to outpace them—potentially leading to the demise of polyploid plants.
This risk is partially why most genome duplications fade from existence. Van de Peer and his team aimed to grasp the factors behind the prevalence of modern polyploidy versus its apparent scarcity in ancient times.
They started by compiling a database of all 470 flowering plant genomes that have been sequenced, including wild types and agricultural crops globally. The researchers examined the DNA for clusters of repeated genes—indications of ancient genome duplication events.
“Not all plants exhibited this,” Van de Peer acknowledges, though some did. They then referenced the fossil record to date when various plants originated, identifying when specific duplication events transpired.
The outcomes were telling. “These whole genome duplications,” Van de Peer states, “do not happen randomly. They are time-clustered.”
A polyploid’s superpower
Specifically, these duplications primarily occurred during major environmental upheavals over the last 150 million years, such as critical cooling or warming periods.
One significant clustering took place approximately 66 million years ago, coinciding with an asteroid impact that obscured the skies and is believed to have wiped out dinosaurs—and over half of all plant species.
Yet, many polyploid plants seem to have weathered this storm better than their non-polyploid counterparts. Despite the downsides, it turns out that polyploid plants exhibit exceptional resilience to environmental stress, functionally acting as a set of “hopeful monsters,” according to Van de Peer.
Stress factors such as prolonged temperature alterations or changes in light could particularly favor polyploid plants. “They might have an edge in photosynthesis, for example, as they possess more genes to harness the available light,” he explains. “This gives them a leg up over many other plant lineages that haven’t undergone whole genome duplication and subsequently went extinct.”
To put it another way, polyploidy acts like an insurance policy. While many plants with extra sets of chromosomes typically fade away, in rare moments of extreme upheaval, they thrive. Their descendants—often shedding those extra chromosome sets—still retain traces in their DNA from the duplications that helped their lineage survive.
Sandra Pitta, a plant biotechnologist at Argentina’s National Scientific and Technical Research Council who wasn’t part of the study, describes the paper as “very rigorous.” She adds, “It gives us a lot of hope.”
This sense of hope is particularly relevant today, as our planet confronts climate changes that polyploid plants might withstand. Such insights could also benefit plant breeders like Pitta, who notes, “If polyploidy helps them resist more types of stress, that’s invaluable.”
What seems like a potential dead end can sometimes pay off down the line—a clever survival trick these plants have locked away.
