By Bob Cooke
Now that abundant ferns are greening gardens, forests and roadsides in Bolton and similar environments, it’s a surprise to learn that all the world’s ferns once almost disappeared, robbed of sunlight by bigger, fast-growing, shade-making flowering plants.
In fact, fossil evidence has shown that far back in evolutionary history, the ferns were the dominant land plants before the age of the dinosaurs. But then, some 200 million years ago, the vigorous, big-leafed flowering plants took root, gradually shoving the ferns aside. It seems the ferns were being shaded into extinction.
The ferns’ problem was that, like other plants, they are dependent on the phenomenon called photosynthesis, the remarkable process by which living plant cells capture the energy of sunlight. The sun’s energetic particles, photons, power the production of sugars from carbon dioxide and water, with leftover oxygen being released into the atmosphere. That’s vital for life on Earth; it’s why we have food to eat and oxygen to breathe.
So, how did the ferns finally cope with too much shade and the danger of extinction?
According to a research team at Duke University, in North Carolina, rescue came in the form of genetic engineering – accidental genetic engineering – that allowed the ferns to survive, rebound and proliferate, and evolve into the many kinds of ferns we see today. That’s why we encounter so many ferns growing abundantly now, widely dispersed here in our local environment and elsewhere.
According to molecular biologist Fay-Wei Li, a graduate student at Duke who led the research, somewhere, somehow a fern plant or a fern spore (its reproductive system) managed to capture a specific gene from another plant, probably a relative of the mosses, called hornwort. That extra gene provided the ability to use the red light, as well as the blue light, that comes streaming down as part of the sun’s spectrum.
Li’s scientific report on this odd bit of genetic trading was published recently in the “Proceedings of the National Academy of Sciences.”
“The acquisition of hornwort neochrome (the new light receptor) appears responsible for the expansion of the fern lineage in the shade of angiosperms,” the flowering plants, explained biochemist J. Clark Lagarias, at the University of California, Davis. He noted that this gene was probably created when two existing genes were spliced together by a virus in some fungus or algal cell. It subsequently got passed to hornwort, and then into the ferns. Fortunately for the ferns, it proved to be very useful, supplying the energy needed for survival.
“Many viruses will transport genes from one species into another,” and for the ferns that “was the only way it could happen,” Lagarias said.
Although such sharing of individual genes among different species seems unusual, it is not unknown. Doctors encounter it all too often when bacteria – which swap genes around among themselves like so much loose change – share resistance to antibiotic drugs with each other, making infections more difficult to treat. Many patients suffer longer, or may even die, as a result of drug resistance genes being shared among micro-organisms.
Also, some bacteria are known to transfer genes from plant to plant, causing plant diseases such as crown gall. So natural gene-swapping is not unknown. And beginning in the 1970s, biologists learned how to move genes artificially, launching genetic engineering as a major industry. This is particularly true in agriculture and drug production, and more recently in attempts at cancer treatment.
So, by capturing and exploiting a different part of the sun’s light spectrum, the ferns seem to have found a timely way to avoid extinction. This new gene gave them a way to collect sufficient energy to grow in the shade, which is where we see them growing so vigorously now.