We've all heard the iconic Greek legend of the Trojan Horse, but what if I told you that microorganisms have been doing this for millions of years. I'll tell you about it in this article but first let's refresh our memory with a little history.
# # # Legend of the Trojan horse # # #
Thousands of years ago, during the war between the Greeks and the Trojans, the cunning Greeks hatched a plan to infiltrate the city of Troy. They built a huge wooden horse, big enough to hide a group of warriors inside. After feigning a retreat, the Trojans, confident of their victory, celebrated and brought the horse to their city as a war trophy.
However, in the dead of night, the Greek warriors dismounted from their horses and opened the gates of Troy. Thus, the Greeks managed to enter the city without any resistance and completely plundered it. The Trojans realized the deception too late and suffered a devastating defeat.
A story that surprises everyone, no ¿Well, although it may be hard to believe for some, nature takes advantage of us. Something similar to the Trojan horse legend occurs between pathogenic microorganisms and their hosts.
Just as the Greeks hatched a cunning plan, pathogens look for ways to infiltrate the host without being detected by defense systems. To do this, they use different strategies, such as masking themselves (by modifying the components of their cell wall and not being recognized) or using evasion mechanisms to go unnoticed by host defense systems (by blocking cell watchdogs, called receptors). (enzymes inhibiting defense or sweeping away any trace of their presence). And once inside the host, they unleash their own army of warriors, the so-called effectors.
# # # And what are effectors # # #
These are generally small proteins secreted by the pathogen inside the host and whose mission is to open the doors so that infection can occur, either by modifying the structures, by inhibiting the proteins defense, by blocking receptors or regulating different mechanisms of host cells from immunity and their structure to the movement of nutrients and apoptosis (programmed cell death that cells activate as a defense against, for example, the case of 'an infection). Simply put, they defeat the host cell's defense mechanisms and take control of it.
# # # Let's look at some examples # # #
Most pathogens, after infecting their host, kill the host's cells and feed on the released nutrients, components and proteins. However, there is a group of pathogens that clearly account for these evasion strategies aimed at circumventing the defenses of the immune system, the obligate biotrophic fungi. But what do obligate biotrophs mean? This means that they only grow in the living cells of their host (and not even remotely on an artificial laboratory medium) so it is vital for them that their host's cells remain in life as long as possible and for this, they must go unnoticed during this period. Infection, especially in the early stages of infection until they introduce their “Trojan horse” into the host.
We see one such great example in the interaction of powdery mildews and their host plant.
This is a type of fungus that lives only on the living cells of its host. To guarantee their survival, after breaking the cell wall, they introduce their Trojan horse inside, a structure called a haustorium, then they release effectors which will manipulate the host cells, inhibit defenses and redirect nutrients towards the site where the infection develops, such as a sink”. All this without the plant defending itself. It is curious that where the fungus develops, everyone expects to see a bad appearance of the leaf or chlorosis but this is not the case, quite the contrary, as the leaf begins to turn yellowish or chlorotic, it is located just below where the fungus grows. we can observe an intense green and a better appearance of the leaves, what we call “green islands”.
This fungus, just like the Greeks with the Trojans, deceives the plant and kills it without it having time to detect it, let alone defend itself.
# # # Future applications # # #
This approach leads to the development of new pathogen therapies to direct research toward a way to unmask the pathogen instead of killing it so that the host can see it and be the one to kill it, thus promoting the creation of an immune memory in this regard. Pathogenic in the host and be more respectful of the environment, because, we must not forget that all microorganisms are NOT harmful, there are many microorganisms that create beneficial interactions with their host by providing them protection, nutrients and resources but We will talk about this in more detail in another article.
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