Plants also have immune system

When biologists learn about immune systems, we usually hear only about humans. Recently I have been studying about plant immune system for one of my courses, and have found it very interesting.  In wilderness plants are constantly exposed to all kinds of microbes and diseases, but they rarely get sick, because their immune system has evolved to literally fight the pathogens that may infect them.

As in mammals, plants possess physical barriers that protect them from the entry of pathogens. In fact, plants have been smarter than us in this manner: each cell has a complex layer of polymers, strategically located surrounding it:  the cell wall (which animal cells lack). One important component of the innermost layer of cell walls is lignin, because it is made of monomers hard to degrade that bond to each other randomly. Because of the random bonding, pathogens will be facing different polymeric structures every time, hence it is going to be difficult for them find a mechanisms to brake all the many random bonds between monomers and therefore infect the plant.

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Lignin molecules are different from each other because of the random bonding, then most pathogens will get confused. Drawing by Hernán Capador

If pathogens can overcome the cell wall, plants will recognize them using specialized proteins- similar to antibodies in humans. Once plants recognize pathogens, they will trigger a signal cascade to activate what is called inducible immune system or basal response that is based on the release of molecules that will fight the pathogen and prevent infection. Nonetheless, pathogens always fight back. Many bacteria possess what is called the type III secretion system, a smart device that allows them to introduce a stylet-like structure in to the plant cells. Throughout the structure, bacteria will leak in molecules that will interfere with the basal response, hence they will be able to survive and take over the plant.

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Plants can recognize bacteria and trigger a signal cascade to fight the disease. However, bacteria can hijack the signal and infect plants. Animation by Hernán Capador.

But plants can still fight back and stop infection. They have also evolved to produce intracellular molecules that will recognize the proteins injected through the type three secretion system. These proteins, called “R” or resistance proteins will trigger again the inducible immune system, and if the infection is severe they will recur to one extreme strategy: suicide. This is a phenomenon called programmed cell death, and it is very useful, as plants will kill infected cells to stop the spreading of infection and prevent it to take over the whole organism.

This is only a glimpse of plant immune system. More can be found in this review paper by Dodds & Rathjen (2010), and in this other review by Barros and collaborators (2015) (By the way, one the collaborators is my teacher on this topic. Very cool huh?)

Please, do not hesitate to comment or ask something below!

Best!

Hernán.

 

7 thoughts on “Plants also have immune system

  1. Hi!
    Yeah! I agree with you that it´s really a interesting subject. Although coming from SLU with much biochemistry.. maybe you should mention that plants actually suffer very much owed to many diseases. Fungi is more ore less present in every other tree but it can cope as long the rest of the life etc… is functioning. Have seen many beautiful trees in my life suffer for fear of spreading of diseases. Just a tip! The best:)

    1. Hi! It is indeed really interesting! Thank you for the tip, I think you are right, even more when we talk about agriculture and agroforestry. Actually plants suffering from diseases is what pushes me to study more about the immune system and the relationships between microbes and plants!

      I agree with you, a lot of molecules and biochemistry. Actually, this topic is part of a course I am currently taking at Stockholm University. I think it will be helpful to make some applied agricultural research in the future.

      Thank you for commenting!
      Best!

      Hernán.

    1. Hello again Muba! This answers my question on the previous reply to your comment. Do you know how serious it is?

      About the link you shared, it says they found it in Denmark and Germany indeed. However, I cannot find any reference to it in the article they cite from Olivera et al., 2015.

      Best,

      Hernán.

      1. Hej Hernan,

        The collected stem rust samples in Sweden, was analysed in the Global Rust Reference Center, Flakkebjerg, Denmark. Thereafter, they detected as TKTTF race. You may contact them for details. Yes, you are right they mentioned, Denmark and Sweden. However, so far as I know they detected in Sweden too. I think somewhere in Gotland.

  2. Stem rust is very serious disease that significantly reduce grain yield from 70 to 100%. For example, in more than 50 years stem rust was not seen in Germany, but suddenly an outbreak was detected as TKTTF race. I think this race was detected in Ethiopia and Turkey, but somehow they migrated to Europe. However, due to this climate change scenario anything could happen. I think an appearance of the TKTTF race was kind of alarm to European wheat growers in order to be ready, but this is my guess.

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