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For modern people, they will experience three questions a day:
What to eat in the morning? What to eat at noon? What's for dinner? Sometimes I can't think of it, so I simply don't eat it.
How nice it would be if we could fill our stomachs with the sun. But this is not possible, because we know that animals cannot photosynthesize.
However, there is an animal that does not recognize life, and it turns itself green in order to survive.
And this green is also quite completely green, it has become a walking "green leaf".
Fortunately, green can rely on photosynthesis to survive for a lifetime, and never worry about eating and drinking.
But before that, it must first "steal" the chloroplast from the plant.
What is even more amazing is that in order to make good use of chloroplasts, it actually "steals" the genes of other organisms.
So, what kind of enlightenment will such a magical animal bring to mankind? What is the so-called "gene thief" in nature?
The green-leaved sea squid (hereinafter referred to as the sea slug) is a member of the large family of sea slugs*
As an animal of gastropods , it has two striking antennae at the tip of its body.
In fact, in infancy, its whole body is reddish-brown. Like modern fat houses, the biggest pleasure of the sea cow is staying still.
Don't look at these cubs as strange, but they have many natural enemies. For example, reef fish, shrimp and crabs, and octopuses are its natural enemies.
Note: Sea slugs are just a common name, generally referring to "shellless snails"*, are mollusks that retain a small number of shells or have no shells.
A type of sea slug
Although they lie down all day, they can escape as fast as they are attacked by predators.
In this way, they are always on the line of life and death, and there is no peace.
Therefore, in order to stay at home with peace of mind, the sea slugs family will find ways to disguise themselves.
The green-leaved sea cow starts with its favorite food, algae.
When they nibble on algae, they do not completely digest and excrete it, but use some care to secretly incorporate the chloroplasts into their bodies.
Scientists call this phenomenon of stealing chloroplasts as used, called stealing plastoids
Immediately after, their bodies will slowly turn green, easily camouflage themselves.
Even the smartest octopus would think these were walking green leaves!
Of course, the chloroplasts that have been painstakingly "stolen" do not seem to be merely self-preservation.
Scientists believe that it can also photosynthesize like plants and obtain energy.
In this way, the sea cow can find a place where the sun can be basked.
But the question is, sea cow, from which kind of algae stolen chloroplast?
As early as the 1970s, scientists began to study this interesting problem.
They tirelessly repeatedly observed the life habits of the sea cow and eventually locked in the target.
It turns out that when they are young, they will actively look for an algae called coastal insulation algae. It is a eukaryotic algae that lives mainly in shallow pools and salt marshes on the east coast of the United States.
They don't eat this algae as soon as they find it, but they have to spend many days together and then eat it, and the way to eat it is far less simple than we think.
First, their tongue teeth puncture the algae cell wall and digest and absorb it with the digestive system.
As the research progressed, researchers found that other sea slugs can also steal chloroplasts.
Unlike the green leafy sea squid, these sea slugs can store chloroplasts in the horned gills, thus using photosynthesis.
We know that no matter how much energy we store, we will dry up one day. This is especially true of the "stolen" chloroplasts.
Because chloroplasts are constantly being depleted, these sea slugs need to constantly replenish chloroplasts in order to maintain photosynthesis.
Sea slugs of various shapes
However, researchers have found that the chloroplasts in the green-leaved sea bull are inexhaustible.
The sea cow can maintain the long-term stability of the chloroplast, completely get rid of the diet and enter the "valley" state.
That is to say, as long as the chloroplast is absorbed, it can spend nearly 10 months without eating or drinking.
You know, the life span of a green-leafed sea cow is only about one year. This is also why everyone says that it can live a lifetime as long as it eats once.
So, how exactly does it keep the chloroplasts in its body functioning?
Studies have found that the green-leaved sea slugs are not only able to absorb chloroplasts, but also actively "steal" genes.
Wait, biological genes do not all come from parents, how can they still rely on "stealing"?
In fact, in nature, the example of "stealing genes" may be much more common than humans think. This could be a more efficient evolutionary shortcut for organisms.
For example, to "steal" genes that can help living organisms necessary for survival may not have to undergo millions of years of painstaking evolution when they easily possess these survival capabilities.
Unlike parent-offspring "vertical transmission", this way of "stealing" genes is seen as "horizontal gene transfer (HGT)"
Current research suggests that horizontal gene transfer is an important phenomenon that complicates the early evolutionary relationships of organisms.
Trees of life showing vertical and horizontal gene transfer
For example, snow algae, which lives in extreme cold climates, is a creature that "steals genes".
In order not to allow ice crystals to pierce an organism's cell membrane, snow algae must produce a protein that binds to ice.
These genes are very similar to some genes of bacteria, archaea, and fungi, and can be regarded as necessary genes for survival in extreme cold environments. In warmer regions, no algae carries this gene.
Therefore, scientists believe that the genes necessary for survival are obtained through horizontal gene transfer.
Snow algae
The relationship between the green leafy sea cow and the coastal insulation algae we see now is also a classic example of horizontal gene transmission in real life.
The study found that the green leaf sea bull can integrate the parts of the algal nuclear gene that encode the chloroplast protein into its own genes. That's why they only need to turn green once, and they can live a lifetime without worry.
On the other hand, this algae and the green-leaved sea slugs can also be regarded as a special "symbiotic relationship".
Speaking of which, we have to mention a famous conjecture in biology - the "theory of the origin of internal symbiosis".
Konstantin Meleshkovsky's 1905 diagram of the tree of life shows that the origin of complex life forms is caused by two stages of symbiotic action, namely the combination of symbiotic bacteria, which in turn form the nucleus and chloroplast
This conjecture suggests that 1.5 billion years ago, free photosynthetic bacteria were engulfed by heterotrophic eukaryotic cells.
But strangely, this time it was not absorbed, but retained.
Photosynthetic bacteria continue to produce energy to sustain themselves, and the excess energy is absorbed by eukaryotic cells, forming a mutually beneficial balance between the two. This balance eventually led to the integration of the two, gradually forming a strange symbiotic relationship – the inner symbiosis.
This conjecture is not empty. Found in chlorinated carboniferous moss plants, they obtain chloroplasts from green algae and even retain extra nuclei. Many eukaryotes have also hijacked the plastids of red algae, even in pathogens Malaria parasites and Toxoplasma gondii.
Observation of mammalian lung cell mitochondria with transmission electron microscopy
The coastal aerobic algae eaten by green-leaved sea slugs are called secondary intra-symbiotic relationships. Because the ancestors of the coastal aberrant algae may have already experienced an endophyte.
As a branch of eukaryotic algae, one of the primitive red algae is engulfed by another type of eukaryotic cell and transfers genes into the genome of the host, thus forming a coastal aerobic algae.
In this way, the green-leaved sea slugs get at least second-hand genes.
However, scientists do not agree with this view, believing that the chloroplasts in the sea cow are not photosynthetic. They found that in the dark, some of the sea cows could survive.
Therefore, they think that the usual observed sea slugs may be like hibernating animals, eating a large meal for several months.
Still, the mainstream view in academia is that chloroplasts play a full role in the sea cow. Because scientists have found that under different light conditions, the hungry sea cow has obvious differences in body length and mortality.
They believe this is due to the photosynthesis of chloroplasts in symbiotic sea cattle.
Every discovery in science raises more questions, and we are pushing the boundaries of human knowledge in answering them.
At present, science believes that the green leaf sea cow "seized" the coastal insulation algae nucleus gene, which is the only functional gene transfer between multicellular animals.
For humans, this method of hijacking genes from other organisms is likely to be used to create a new medical protocol for treating genetic diseases.
For example, in the future, medical experts can obtain genes from other organisms for the treatment of some human diseases and so on.
Perhaps one day, scientists can create artificial chloroplasts that work outside the body of plants and harvest solar energy directly to meet human needs.
At that time, as long as we are basking in the sun, we will be full, and we will be able to cultivate immortals into super fat houses.
But in this case, will human beings also lose the endless pleasure of being a foodie?
*References
Nudibranch.Wikipedia. on 14 July 2019, at 13:49 (UTC).
David Smith. Steal My Sunshine. The scientist. 2013.
Dan Graur. Mitochondria Are Just Like Pigs: Ingesting Them May Lead to the Establishment of Stable Endosymbiosis with Humans.Judge Starling. 2016.
Kate Horowitz. 7 Vivid Facts About Sea Slugs. mentalfloss.com.
fengfeixue0219. Green leafy sea bull: capture genes for photosynthesis. Nutshell. 2015.
Photosynthetic animals, sea slugs: a beautiful soap bubble burst Author: Niu Dengke Science Network
Nature's "gene thief" Li Zhongdong Science Popular Magazine 2018-12-14