A weird-looking parasitic plant has discarded all its photosynthesis machinery – and nevertheless has found a way to thrive.
A new analysis of seven Balanophora species has found that these crazy plants have reduced their plastid genomes, or plastomes – the parts of their cells that oversee photosynthesis – by a factor of 10.
What remains, a mere 16,000 base pairs at most, represents a vestigial relic that's useless for converting sunlight into energy, a process most plants rely on to survive.
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Instead, Balanophora takes its cues from the mushrooms it so closely resembles, tapping into tree roots to slurp up their nutrients. Unlike symbiotic mycorrhizal fungi, though, Balanophora gives absolutely nothing back; it's a parasite, through and through.
"Balanophora has lost much of what defines it as a plant, but retained enough to function as a parasite," says botanist Petra Svetlikova of the Okinawa Institute of Science and Technology in Japan.
"It's a fascinating example of how something so strange can evolve from an ancestor that looked like a normal plant with leaves and a normal root system."
Balanophora produces flowers and seeds, but its appearance and behavior are so similar to those of a mushroom that Svetlikova and her colleagues wanted to know more about its evolutionary journey. This resemblance is an example of convergent evolution, wherein two very different, unrelated species develop remarkably similar traits.
The researchers sampled seven species from 12 populations in their hard-to-reach habitats across Taiwan and Japan, and analyzed their genetic code.
They found that Balanophora has some of the smallest plastomes ever recorded among land plants, with just 14,000 to 16,000 base pairs, compared with the 120,000 to 170,000 base pairs typical of most plants.
Despite this, their remaining tiny plastome is still metabolically active, just not for photosynthesis. This suggests that these fascinating plants don't harbor as many redundant genes as previously thought, but retain just enough of their plastid machinery to support essential metabolism in a parasitic lifestyle.
The researchers also found that the plastome loss occurred in a common ancestor, before Balanophora diverged into many separate species.
Balanophora species isolated on islands subsequently evolved the ability to reproduce asexually. In fact, in some species, that's now the only way they can reproduce.
This strategy is rarely seen in obligate systems in plants, and one that the researchers say likely boosts the parasite's chances of establishing new populations on islands, where finding mates – or even suitable habitat – can be difficult.
Earth is the only world on which we know for a fact that life has emerged. This scarcity would suggest that life is fragile – but the tenacity with which organisms adapt and cling to existence is nothing short of astonishing.
"Balanophoraceae thus emerge as a fascinating model for reconstructing the evolutionary changes associated with photosynthesis loss in land plants," the researchers write in their paper.
The research has been published in New Phytologist.