Immune Response of Plants – Part 1

19.09.2017  /  Scienceandmore  /  Category: Plant Biology

Plants represent a rich source of nutrients that is desired by microorganisms, which are mainly represented by bacteria but also fungi. To prevent exploitation, plants have developed an array of structural and chemical defence response mechanisms against infestation with pathogens. These pathogens are divided into the categories biotrophic, necrotrophic and hemibiotrophic. Biotrophic pathogens keep the host plants alive while feeding on them. Necrotrophic pathogens produce degrading enzymes to release plant nutrients and, thereby kill the plant. Hemibiotrophs behave in their early stages of infection like biotrophs, but eventually become necrotrophic during latter stages (1).

Structural plant defence

Their first line of plant defence is the structural defence and comprises of the waxy cuticle, consisting of a complex polymer of esterified fatty acids coated with waxes, and rigid cell walls as exterior surface that prevent pathogens from invading the plant. The structural defence is always present and does not need to be induced. This alone, however, is not adequate against all pathogens, so plants possess inducible immune responses that are activated upon pathogen attack (2,3).

Inducible plant defence

The currently well-established model of plants’ inducible immunity was proposed by Jones and Dangl in 2006 (4) and explains the interaction of plant and pathogen in a zig zag model. This model describes the possible interactions between plants and pathogens as two-pathed and four-phased, as follows. The first path consists of receptors on the surface of cells (pattern recognition receptors, abbreviated with PRRs) that recognise certain features of microorganisms that are called microbe-associated molecular patterns (MAMPs). This path is called pattern-triggered immunity (PTI), since the recognition of MAMPs can induce the plants immune response.

The second path is located mostly inside the cell and consists of certain plant proteins that are encoded by plant resistance genes (R genes). These plant proteins interact with proteins from the pathogenic microorganism that are called effectors or avirulence factors (encoded by avirulence genes) and aim to interfere with the plant immune response in order to alter/suppress it and mask the pathogen’s presence. This path is called effector-triggered immunity (ETI). Here, the term avirulence is somewhat misleading as it implies the loss of virulence, i.e. the loss of the ability to infect plants. Effectors (avirulence-factors) contribute to the pathogens virulence; however, these factors can be recognised by the plant proteins that are encoded by R genes. In case of recognition, plant immune responses are activated and the pathogen does not infect the plant and is, therefore, avirulent.

The four phases

In the first phase of plant-pathogen interaction, the plant recognises MAMPs and activates PTI to stop pathogen growth and colonisation. In the second phase, successful pathogens use effectors that interfere with the plant’s PTI, leading to effector-triggered susceptibility (ETS) in the plant. These effectors thus increase the pathogen’s virulence. If the plant recognises the microbial effectors with R gene-encoded proteins, then the third phase is triggered, activating ETI. In the fourth phase, natural selection favours the pathogens which have abandoned or modified their recognized effectors, or alternatively gained unrecognised effectors, meaning that the pathogens suppress ETI, again leading to ETS (see figure) (4). It is important to understand that this is not a chronological sequence where PTI is followed by ETS, followed by ETI, and so on, but should rather be considered as evolutionary adjustments to increase virulence on the pathogen side (abandonment/modification of recognized effectors, or gain of unrecognised effectors) and immunity on the plant side (recognition of MAMPs and effectors). It could be compared to an “arms race” on an evolutionary timescale.

Zig Zag model of plant immune response against pathogens. HR = Hypersensitive Response (in reference to Jones and Dangl in 2006).

Pattern-triggered immunity (PTI)
Pathogenic bacteria can enter through stomata (surface openings that are needed for gas exchange of the plant) and other openings such as wounds, into the plant where they proliferate. Fungi enter directly into epidermal cells or penetrate the plant with their hyphae (filamentous structures of fungi) between and through cells. At this point, the plant’s PRRs perceive MAMPs and transmit signals to the cell (4-6).
The best described MAMPs are fungal chitin, bacterial peptidoglycans and lipo-polysaccharides, and bacterial flagellin (1,6,7). MAMPs are in general abundance and their nature is essentiality for microorganisms. Fungal chitin is an essential integral component of fungal cell walls and estimated to be the second most abundant polysaccharide in the world (besides cellulose); bacterial peptidoglycans are essential integral components of bacterial cell walls; lipopolysaccharides are membrane components of Gram-negative bacteria; bacterial flagellin is a component of the bacterial flagellum, which is used for locomotion (widespread among different species). This essential character often requires conservation throughout evolution and alteration could lead to a loss of microbial fitness and virulence for pathogens. The flagellum for example is not essential for bacterial survival, but contributes strongly to the virulence of bacterial pathogens (5).
Activation of PTI characteristically triggers reactive oxygen species (ROS) production, expression of pathogen-resistance genes (PR genes), callose deposition in the plant´s cell walls and closure of stomata as the main reactions to adjust the plant to pathogen attacks (1,4,7). ROS act as signalling molecules inside the plant but also as defence components, due to their reactive properties, to damage and kill pathogens. PR gene products can be active components against pathogens or can be involved in signal transmission. Callose strengthens the cell wall, and the closure of stomata decreases possible entry points for additional pathogens.
Effector-triggered immunity (ETI)
As stated before, pathogens additionally use effectors to alter the plants immune response, and mask their presence from the plant. Effectors increase the plant’s susceptibility, enhance microbial fitness, and can cause nutrient leakage for nutritional purposes of the pathogen (4,5,9).
At this point, microbial effectors may be either directly or indirectly recognised by the plant’s R-gene products, which leads to an activation of ETI. There are two hypotheses that describe the recognition of microbial effectors by plant’s R gene products. The first states that the R gene products in general directly recognise microbial effectors, and this is called the gene-for-gene hypothesis. The second, called the guard hypothesis, describes indirect effector recognition by R gene products. Effectors manipulate certain plant components as their targets and, rather than being recognised directly, R gene products recognise the resultant alteration of the targeted components. Therefore, R gene products ‘guard’ specific components and recognise a ‘modified-self’. This way, a limited set of R gene products can cover a wider range of microbial effectors. Most R genes encode NB-LRR (nucleotide-binding leucine-rich repeat) proteins, and only approximately 150 NB-LRR genes are found in A. thaliana, an important model plant in biology; a number that would be insufficient to cover all known and potential microbial effectors. This fact supports the guard hypothesis (3,4,9,10).
PTI is understood to be the first line of defence against the majority of pathogens, mainly triggering weaker and rather localised defence responses, such as ROS accumulation, while ETI is more specific and triggers mainly stronger responses, such as hypersensitive response (HR). HR is a form of programmed cell death that is triggered at the site of infection and is understood to cut off pathogens from water and nutrients, thereby limiting proliferation (9,12). However, the reversed case is not excluded and suggests that the specific character of the MAMP or effector, as well as their quantity and exposure time, together modulate a specific plant immune response (8,11).

Recently, the zig zag model for plant-pathogen interaction was criticised since it is based on the plant’s interaction with biotrophic microbes, i.e. pathogens that keep their host plans alive while feeding on them, and lacked integration of symbiotic interactions, or the response to necrotrophic pathogens where HR would rather be a favourable result, since necrotrophic pathogens aim to kill plant cells in order to obtain nutrients. HR, which is a form of programmed cell death would, therefore, contribute to an invasion by necrotrophs and be counterproductive for the plant.

Immune Response of Plants – Part 2


1. Freeman, B. C. and Beattie, G.A. (2008) An Overview of Plant Defenses against Pathogens and Herbivores. The Plant Health Instructor. Available from: DOI: 10.1094/PHI-I-2008-0226-01

2. Sels, J., Mathys, J., De Coninck, B.M.A., Cammue, B.P.A., and De Bolle, M.F.C. (2008) Plant pathogenesis-related (PR) proteins: A focus on PR peptides. Plant Physiology and Biochemistry 46:941-50.

3. Kim, M.G., da Cunha, L., McFall, A.J., Belkhadir, Y., DebRoy, S., Dangl, J.L., Mackey, D. (2005) Two Pseudomonas syringae Type III Effectors Inhibit RIN4-Regulated Basal Defense in Arabidopsis. Cell, 121(5), 749-59.

4. Jones, J.D. and Dangl, J.L. (2006) The plant immune system. Nature, 444, 323-9.

5. Pel, M.J.C. and Pieterse, C.M.J. (2013) Microbial recognition and evasion of host immunity. Journal of Experimental Botany, 64(5), 1237-48.

6. Yeh, Y.H., Chang, Y.H., Huang, P.Y., Huang, J.B., Zimmerli, L. (2015) Enhanced Arabidopsis pattern-triggered immunity by overexpression of cysteine-rich receptor-like kinases. Front. Plant Sci., 6, 322.

7. Quirino, B. F. and Brent, A. F. (2003) Deciphering host resistance and pathogen virulence: the Arabidopsis/ Pseudomonas interaction as a model. Molecular plant pathology, 4(6), 517-30.

8. Doehlemann, G. and Hemetsberger C. (2013) Apoplastic immunity and its suppression by filamentous plant pathogens. New Phytologist, 198, 1001-16.

9. Coll, N.S., Epple, P., Dangl, J.L. (2011): Programmed cell death in the plant immune system. Cell Death and Differentiation, 18, 1247-56.

10. Alfano, J. R., Collmer, A. (2004) TYPE III SECRETION SYSTEM EFFECTOR PROTEINS: Double Agents in Bacterial Disease and Plant Defence. Annual Review of Phytopathology, 42, 385-414.

11. Nishimura, M.T. and Dangl, J.L. (2010) Arabidopis and the plant immune system. The Plant Journal. 61, 1053-1066.

12. Torres, M.A., Jones, J.D.G., Dangl, J.L. (2006) Reactive Oxygen Species Signaling in Response to Pathogens. Plant Physiol., 141(2), 373-8.



  1. Hola! I’ve been following your web site for a long time now and finally got the courage to go ahead and give you a shout out from Houston Tx! Just wanted to tell you keep up the great job!

  2. duck onesie says:

    Heya outstanding blog! Does running a blog like this take a great deal of work? I’ve absolutely no knowledge of programming however I was hoping to start my own blog soon. Anyway, should you have any recommendations or techniques for new blog owners please share. I understand this is off topic however I simply had to ask. Kudos!

  3. This is really interesting, You are a very skilled blogger. I’ve joined your rss feed and look forward to seeking more of your great post. Also, I’ve shared your site in my social networks!

  4. Pingback:
  5. Pingback: follow this link
  6. Pingback: read article
  7. Pingback:
  8. Pingback:
  9. Pingback:
  10. I’m compiling my latest list. I’m sorry there hasn’t been any recent updates.

    I’ve had some problems building the list along the way.
    I’ll talk more about that at a later date.

  11. Pingback: click to continue
  12. I do not even know how I ended up here, but I thought this
    post was great. I don’t know who you are but definitely you’re going to a famous blogger if you
    aren’t already 😉 Cheers!

  13. Attractive element of content. I just stumbled upon your blog and
    in accession capital to claim that I acquire in fact enjoyed account your weblog
    posts. Any way I’ll be subscribing for your feeds or even I achievement you access consistently fast.

  14. I used to be recommended this web site by way of my cousin. I’m no longer certain whether this submit
    is written by him as no one else know such unique approximately my trouble.
    You’re wonderful! Thank you!

  15. Hey there, I think your website might be having browser compatibility issues.
    When I look at your website in Opera, it looks fine but when opening in Internet Explorer, it has some overlapping.
    I just wanted to give you a quick heads up! Other then that,
    fantastic blog!

  16. It’s remarkable to go to see this site and reading the views
    of all colleagues about this post, while I am also zealous of getting experience.

  17. Heya i’m for the first time here. I found this board
    and I find It really useful & it helped me out much.
    I hope to give something back and help others like you aided me.

  18. minecraft says:

    Great information. Lucky me I found your website by chance (stumbleupon).
    I’ve bookmarked it for later!

  19. minecraft says:

    This info is worth everyone’s attention. Where can I find out more?

  20. I and also my guys were reading through the great tips and tricks on your website while immediately I had an awful feeling I had not expressed respect to the web site owner for those techniques. All of the boys had been passionate to learn them and have really been taking advantage of these things. Many thanks for truly being well considerate and also for getting varieties of cool themes most people are really eager to be informed on. My honest apologies for not expressing appreciation to you sooner.

  21. minecraft says:

    Great post. I was checking constantly this blog and I am inspired!
    Very useful info specially the remaining part 🙂 I care for such info a lot.
    I was seeking this particular info for a very long time.
    Thanks and good luck.

  22. minecraft says:

    Great post. I’m facing a few of these issues as well..

  23. minecraft says:

    I am really enjoying the theme/design of your website. Do you ever run into any web browser compatibility issues?
    A handful of my blog readers have complained about my blog
    not working correctly in Explorer but looks great in Firefox.

    Do you have any tips to help fix this problem?

  24. minecraft says:

    Hey! I just wanted to ask if you ever have any
    problems with hackers? My last blog (wordpress) was hacked and
    I ended up losing several weeks of hard work due to no data backup.

    Do you have any solutions to stop hackers?

  25. minecraft says:

    Your style is very unique in comparison to other people I have read stuff from.
    Thanks for posting when you’ve got the opportunity, Guess I’ll just bookmark this web site.

  26. minecraft says:

    Howdy! I just would like to give you a big thumbs up for your excellent info
    you have right here on this post. I am returning
    to your web site for more soon.

  27. Excellent goods from you, man. I have understand your stuff previous to and you
    are just too excellent. I actually like what you’ve acquired here, certainly
    like what you are saying and the way in which you say it.

    You make it entertaining and you still care for to keep it smart.
    I can’t wait to read much more from you. This is really a
    wonderful web site.

  28. I was curious if you ever thought of changing the layout of your website?
    Its very well written; I love what youve got to say.

    But maybe you could a little more in the way of content so
    people could connect with it better. Youve got an awful
    lot of text for only having one or 2 pictures.
    Maybe you could space it out better?

  29. Hey there! Do you use Twitter? I’d like to follow
    you if that would be ok. I’m undoubtedly enjoying your blog and look forward
    to new posts.

  30. Hi there, after reading this awesome piece of writing i
    am as well delighted to share my familiarity here with colleagues.

  31. Ahaa, its good dialogue about this post here at this weblog, I have read all that, so now me also
    commenting at this place.

  32. Wonderful blog! I found it while searching on Yahoo News.
    Do you have any tips on how to get listed in Yahoo News?

    I’ve been trying for a while but I never seem to get there!
    Many thanks

  33. certainly like your web site but you have to test the spelling
    on quite a few of your posts. Many of them
    are rife with spelling problems and I find it very bothersome to tell the truth then again I’ll certainly
    come back again.

  34. Nice post. I was checking continuously this weblog and I’m inspired!
    Very useful information specifically the remaining part 🙂 I care for such information a lot.
    I used to be looking for this certain information for a long time.
    Thank you and good luck.

  35. I’m amazed, I have to admit. Rarely do I encounter a blog that’s equally educative and amusing, and let me tell you,
    you have hit the nail on the head. The problem is something too few men and
    women are speaking intelligently about. I am very happy that I came across this in my search
    for something regarding this.

  36. Hey I know this is off topic but I was wondering if you knew of any widgets I could add
    to my blog that automatically tweet my newest twitter updates.
    I’ve been looking for a plug-in like this for quite some time and was hoping maybe you would have some experience with something like this.
    Please let me know if you run into anything. I truly enjoy reading your blog and I look forward to your new updates.

  37. propulsão says:

    Terrific work! This is the type of info that are meant to be shared across the
    net. Shame on the search engines for now not positioning this publish upper!
    Come on over and seek advice from my website . Thanks =)

  38. Very rapidly this site will be famous amid all
    blogging visitors, due to it’s nice articles

  39. submundo says:

    Appreciate the recommendation. Will try it out.

  40. Are you looking to see and talk to some really sexy girls?
    These girls are super dirty and it doesn’t cost a single cent to talk to
    them. It’s wall to wall babes at this site. Just visit,2778,2777,2776,3391 and sign up
    for your free account. You’ll be talking to these total babes in a matter of
    no time flat!

  41. If some one needs expert view about running a blog after that
    i suggest him/her to go to see this webpage, Keep up
    the fastidious job.

  42. When I initially commented I clicked the “Notify me when new comments are added” checkbox
    and now each time a comment is added I get several emails with the same comment.
    Is there any way you can remove people from that service?
    Thank you!

  43. Thank you for another wonderful post. Where else may
    just anybody get that type of info in such a perfect way of writing?
    I’ve a presentation subsequent week, and I am at the search for
    such info.

  44. I love reading through an article that will make men and women think.

    Also, many thanks for permitting me to comment!

  45. Hi there very cool site!! Man .. Beautiful ..
    Amazing .. I will bookmark your website and take the feeds additionally?

    I’m happy to search out a lot of useful information right here within the publish, we’d
    like work out more strategies on this regard, thank you for sharing.
    . . . . .

  46. My brother recommended I might like this blog.
    He was totally right. This post truly made my day. You
    can not imagine simply how much time I had spent for this information! Thanks!

  47. Excellent web site you have here.. It’s
    hard to find excellent writing like yours these days.
    I really appreciate people like you! Take care!!

  48. If some one needs to be updated with newest technologies afterward he must be pay a
    visit this web site and be up to date everyday.

  49. I used to be able to find good information from your blog articles.

  50. Howdy would you mind stating which blog platform you’re
    using? I’m planning to start my own blog soon but I’m having a tough time choosing between BlogEngine/Wordpress/B2evolution and Drupal.

    The reason I ask is because your layout seems different then most blogs and
    I’m looking for something unique. P.S Apologies for getting off-topic but I had to ask!

  51. suzuran says:

    Peculiar article, exactly what I needed.

  52. Hi there! I know this is kinda off topic but I was wondering which blog platform are you using for this
    site? I’m getting tired of WordPress because I’ve had problems with hackers and I’m looking at
    alternatives for another platform. I would be awesome if
    you could point me in the direction of a good platform.

  53. magnificent post, very informative. I wonder why the other specialists of this sector don’t notice this.
    You should proceed your writing. I am sure, you have a huge readers’ base already!

  54. Great work! That is the kind of info that are supposed to
    be shared around the web. Shame on Google for now not positioning this post upper!
    Come on over and visit my site . Thank you =)

Post a comment