The common mistletoe, a symbol of Catholic Christmas, has proven to be a unique plant kingdom that does not know how to break down sugars with oxygen and use their energy to produce cellular energy, scientists say in an article published in the journal Current Biology.
“Our colleagues recently found that mistletoe lacks genes associated with oxygen respiration in mitochondria. We thought they had “moved” to some other part of the genome, and were amazed when we realized that mistletoe had completely gotten rid of that part of the cell's metabolic machine. It was considered an essential part of the cells of all multicellular creatures,”said Andrew McLean of the John Innes Center in Norwich, UK.
Botanists have found out relatively long ago that some plants have lost in the distant past the ability to photosynthesize and independently extract nutrients, having learned to parasitize on other plants and even fungi. Such representatives of the flora, the so-called mycoheterotrophic plants, are most often found in forests and in dark corners of the area, where other members of the plant world simply cannot survive.
A striking example of such plants are orchids that grow in tropical and temperate forests and parasitize various kinds of fungi, which they trick into supplying themselves with nutrients and minerals. There are dozens of species of other flowering plants that lead a similar lifestyle.
McLean and his colleagues discovered a plant that brought this process to its logical conclusion - it completely lost the ability not only to independently obtain sugars only through photosynthesis, but also to break down "stolen" nutrients using oxygen. It turned out to be the common mistletoe, a parasitic plant whose branches Europeans decorate their homes with during Christmas and New Years.
Analyzing the genome of this representative of the flora, the authors of the article drew attention to the unusually short length of that part of it that controls the work of mitochondria - cellular "energy stations" in which glucose and other nutrients are oxidized and molecules of ATP, a universal cellular "energy currency", are produced.
In the distant past, mitochondria were independent organisms, but later they merged with the ancestors of plants and animals and gradually became part of their cells, having lost almost all genes, most of which "moved" into nuclear DNA. For this reason, the contraction of this part of the genome in mistletoe interested, but not surprised, geneticists.
Nevertheless, there were still reasons for surprise - it turned out that the genes responsible for the work of the so-called "complex I", a key set of mitochondrial enzymes, completely disappeared from both nuclear and mitochondrial DNA. These proteins, as scientists explain, are responsible for "burning" carbohydrates and other nutrients in the cells of all multicellular substances and using their energy for other purposes.
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The question is, how does mistletoe survive then? As further experiments by McLean and his colleagues showed, these plants produce ATP molecules using glycolysis and other “oxygen-free” types of metabolism, whose efficiency is ten times lower.
In addition, some of the molecules of the "energy currency", as scientists suspect, mistletoe simply steals from the owner. Both, according to geneticists, explains why these parasites suck unusually large amounts of sugars from the branches of their victims.
Now McLean and his colleagues are analyzing the DNA of many other parasitic plant species, testing whether mistletoe is truly unique in this regard.
