The plants seemed to have simply ditched their entire chloroplast genome. That was almost unthinkable. Chloroplasts are best known for using light to make food, but like all the food-making organelles called plastids, they contain genes that are involved in many key cellular processes.
Even malaria parasites still carry a plastid genome, Molina noted, and their last photosynthetic ancestor lived hundreds of millions of years ago. Recent research compiled the first draft nuclear genome of a Rafflesiaceae parasite, Sapria himalayana. This shocking finding has now been confirmed by an independent research team from Harvard University.
The draft genome for another member of the Rafflesiaceae family that they recently published in Current Biology is full of surprises, showing how far parasites can go in shedding superfluous genes and acquiring useful new ones from their hosts. He has been trying to reveal their many secrets for nearly 15 years, but a nuclear genome sequence always proved elusive.
Like them, Sapria has done away with many genes considered essential to its free-living relatives. Still, Davis was shocked to see that nearly half of the genes widely conserved across plant lineages had disappeared from Sapria. The only other organisms known to have jettisoned that genome are single-celled algae in the genus Polytomella , which gave up photosynthesis in favor of absorbing sustenance from the waters around them.
Sapria also seems to have cut other genetic corners. The plants have deleted the noncoding stretches of DNA within many genes. These regions, called introns, are interspersed among the parts of genes that code for the actual protein that is produced.
It might sound as though Sapria and its kin have simply made their genomes smaller and more efficient. What is filling up its genome? The passage of genes from distant lineages, such as the corpse flower and its vine host, is known as horizontal gene transfer. Though common in bacteria e. Scientists were first alerted that something was a little off with Rafflesia several years ago. At that time, they were looking at a much bigger picture - the overall evolution of parasitism in plants - when they noticed something a little odd in their data.
For one of the genes, Rafflesia and similarly deeply-embedded parasites didn't appear to be related to their closest kin, and instead, appeared to be cousins of their hosts. They hypothesized that such a strange evolutionary relationship could only have evolved in one way: if the parasites had stolen that gene.
Now, the Harvard team has sequenced all of the active genes of both the corpse flower and its host to determine how many genes were stolen. They also found that most of these genes were incorporated into the parasites own DNA, even replacing similar genes, and another third of Rafflesia 's own genes have evolved to look more like the vine's. The genes that were stolen perform a wide variety of cellular functions, including roles in respiration, metabolism, mitochondrial translation, and protein turnover.
Their active expression suggests that they play a key role in the parasite's survival, but the researchers hope that future research will determine exactly how important these genes are and whether they help the parasite evade detection by the host's immune system.
During the return voyage in , his ship was taken by the British, with whom France was at war, and all his papers and notes were confiscated. They did not see the light of day until when they were rediscovered in the Natural History Museum, London.
The British botanist Joseph Arnold and the statesman Sir Thomas Stamford Bingley Raffles , founder of modern Singapore collected a specimen of another Rafflesia species found by a Malay servant in Sumatra in Arnold contracted a fever and died soon after the discovery. Lady Raffles, who had also been present when the specimen was collected, finished the colour drawing that Arnold had started of the plant, and it was sent to Joseph Banks, along with the preserved material.
Banks passed all the materials on to Robert Brown of the British Museum and Kew's resident botanical artist Franz Bauer William Jack who was Arnold's successor in Sumatra, being aware that Deschamps, despite his loss of notes, could formally publish a name for the newly discovered genus at any moment, rushed to draft a description to ensure the credit went to a British botanist.
This draft description was held in readiness, in case there was word that the French were about to publish, whilst waiting for the British Museum to produce a better-prepared version. The generic name, Rafflesia given in honour of Sir Raffles , proposed by Brown who had originally wanted to call it Arnoldii after Joseph Arnold, was validated by S.
Gray in his report of the June meeting of the Linnean Society of London, as published in the Annals of Philosophy in September that year. While the species Rafflesia arnoldii was officially described for the first time in by Brown, so that Arnold was commemorated after all.
Many sites where Rafflesia grows are now popular with tourists, who provide an income for local people and also an incentive to preserve the species. Unfortunately, as a result of this ecotourism and the resulting human disturbance, the number of flower buds produced per year has decreased significantly at many sites. The flower buds are applied in traditional medicine to promote delivery and recovery during and after childbirth. They are also used as an aphrodisiac.
It is likely that these uses are associated with the shape, colour and size of the buds, and superstitions surrounding the flower, rather than being linked to any chemical properties. The flower of Rafflesia arnoldii is an iconic symbol of the southeast Asian rainforest, and is often used in tourist brochures to symbolise the rich biodiversity of the region's forests. The flower has also been depicted on Indonesian postage stamps on several occasions, while the flowers of related Rafflesia species are often illustrated on the postage stamps of neighbouring southeast Asian countries.
The flower is also used as the symbol of the Flora Malesiana project, which aims to describe all flowering plants from the region between Thailand and Australia. Areas of forest in which Rafflesia arnoldii grows are visited by ecotourists, providing an income for local people and revenue for protected areas. The fruits are eaten by ground squirrels and tree shrews.
For this reason, there is great interest in conserving Rafflesia sites rather than eradicating existing populations as is the case for noxious parasitic plant weeds.
Although preserving as much of its habitat as possible would be the simplest and most obvious way to conserve Rafflesia , this is not currently practical throughout its range. Rafflesia Life History " a penetrating smell more repulsive than any buffalo carcass in an advanced stage of decomposition" Mjoberg, There are approximately 17 Rafflesia species distributed throughout Southeast Asia Nais, ; Meijer, ; Mat Salleh, These species are highly specific as to the hosts that they parasitize, preferring only a few species of Tetrastigma a member of the common grape family that are distributed in the same geographic area.
Although technically a member of the plant kingdom, Rafflesia challenges traditional definitions of what a plant is because they lack chlorophyll and are therefore incapable of photosynthesis as are all members of its family, Rafflesiaceae.
0コメント