An international team of researchers has aligned and analyzed the genome of Sapria himalayana, a rare holoparasitic flowering plant in the family Rafflesiaceae. Their findings, published in the journal Current Biology, offers a unique perspective on how flowering plant genomes can be altered to match an extreme form of plant parasitism.
Sapria himalayana represents the extreme manifestation of the parasitic lifestyle, being completely dependent on its host for aquatic nutrients and photosynthesis.
Its flowers are about 20 cm (8 inches) wide, bright red in color covered with sulfur-yellow spots. They appear above the ground and have a putrid odor.
Sapria himalayanais a more famous cousin, Rafflesia arnoldii, produces flowers up to 1 m (3.3 feet) in diameter, the largest in the world.
“In many ways it is a miracle that these plants exist today, let alone that they appear to last for tens of millions of years,” said Professor Charles Davis, a researcher in the Department of Organizational and Developmental Biology at Harvard University and curator. of vascular plants at Harvard Herbal University.
“They’ve really discarded a lot of things that we identify as a typical plant, yet they’re deeply embedded in the plant tree of life.”
Professor Davis and his colleagues from the United States, China, Malaysia and Thailand followed suit and analyzed the highly modified genome of Sapria himalayana.
Their analysis revealed an astonishing degree of gene loss and surprising amounts of gene theft from its ancient and modern hosts.
These findings bring unique insights into the number and type of genes needed to be an endoparasite, along with new insights into how far the genomes of flowering plants can be altered and still function.
What struck the researchers immediately was the degree of gene loss Sapria himalayana experienced as they left their bodies and adapted to become endoparasites.
About 44% of all genes found in most flowering plants are absent in the genome of Sapria himalayana. This extent of gene loss is more than four times the degree of loss in other plant parasites.
Many of the lost genes include what are considered the key genes responsible for photosynthesis, which converts light into energy.
At the same time the data showed an underlying evolutionary convergence to become a parasite because Sapria himalayana and the parasitic plants the scientists compared them with many of the same kinds of genes despite evolving separately.
They also identified dozens of genes that came in the Sapria himalayana genome by a process called horizontal (or lateral) gene transfer instead of the traditional parent-to-child transmission.
Basically it means Sapria himalayana stole DNA from their host instead of handing it over to them.
The authors then reconstructed the side gene transfers they detected to put together a hidden history of former hosts behind millions.
“We concluded that there is a common genomic or genetic roadmap on how plant parasites evolve,” said Dr. Cai Liming, a researcher at the University of California, Riverside.
Liming Cai et al. Deeply Altered Genome Architecture in the Endoparasitic Flowering Plant Sapria himalayana Griff. (Rafflesiaceae). Current Biology, published online January 23, 2021; doi: 10.1016 / j.cub.2020.12.045