Two mechanisms by which PNAS bacterial RLs activate plant immunity

Responsible Editor | Wang Yi The innate immune response of plants is a complex life activity, which is essential for the healthy growth of plants
.

The Non-self-recognition Invasion Pattern from pathogenic bacteria recognizes and stimulates each other through pattern recognition receptors (PRRs) such as receptor kinases (RKs) or receptor-like proteins (RLPs) on the plasma membrane of the host plant The initiation and transmission of immune signals [1-3]
.

After PRRs are activated, they can recruit other receptor kinases or receptor-like kinases.
Accompanied by the burst of extracellular reactive oxygen species (ROS), changes in ion flux on the plasma membrane (such as Ca2+), activation of kinase activity such as intracellular MAPKs, etc.
, will immune The activation signal is transmitted downstream
.

At the same time, a variety of plant hormones are widely involved in the interaction between plants and pathogens, including salicylic acid (SA), jasmonic acid (JA), ethylene (ET), abscisic acid (ABA), brassinolide (BR) Wait [4-6]
.

Rhamnolipids (RLs) are amphipathic metabolites produced by Pseudomonas or Burkholderia.
They have the characteristics of general surfactants and are mainly composed of rhamnose (L-rhamnose) and 3-( 3-hydroxyalkanolipids) alkanoic acid (HAA) precursor is produced; its hydrophilic group is composed of 1 to 2 molecules of rhamnose ring, and the hydrophobic group is composed of 1 to 2 molecules of saturated or unsaturated fatty acids with different carbon chain lengths Composition [7]
.

RLs can change the hydrophobicity of the bacterial cell surface, which is very important for the spread of germs and the formation of biofilms [8]
.

It has been reported in plants that RLs are involved in plant immunity and resistance
.

However, the molecular mechanism of RLs involved in activating host immunity is still unclear
.

Recently, Stéphan Dorey of the University of Reims, France, in collaboration with Eric Déziel of the Canadian National Institute of Science, and Stefanie Ranf of Technical University of Munich, Germany, published a report entitled Bacterial rhamnolipids and their 3-hydroxyalkanoate precursors activate Arabidopsis innate immunity through two independent mechanisms in the PNAS magazine.
The research paper revealed the mechanism of bacterial rhamnolipid activating plant immunity through two different ways
.

In this study, the researchers first identified the rhamnolipid RLs contained in Pseudomonas syringae through high-performance liquid chromatography (HPLC)-tandem mass spectrometry (MS/MS) analysis, and determined through immune signal correlation determination and genetic analysis RLs can induce immune-related disease-resistant signal transduction in Arabidopsis, and it has been found that this pathway depends on the bulb-type lectin kinase LORE
.

Further analysis of the Ca2+ signal, ROS production, MAPK activation and other activities involved in plant perception by RLs showed that HAAs, the precursors of RLs synthesis, can activate typical PTI-related immune responses (early ROS accumulation) and promote plant resistance to pathogens.
At the same time, RLs can also trigger an atypical immune response (later ROS accumulation) and resistance to Pseudomonas infection.
Although this process does not depend on LORE, it is affected by the composition of sphingolipids on the plasma membrane
.

To sum up the two mechanisms of Arabidopsis HAA and rhamnolipid sensing and integrating immune response, this study reveals for the first time the molecular mechanism of rhamnolipid and its precursors to activate plant immunity, and also shows that plants can sense at the same time Bacterial cell surface molecules and their immediate precursors, which trigger different immune responses
.

It has important theoretical value for in-depth understanding of plant immunity process, which is helpful to promote the further application of rhamnolipids in the field of agriculture
.

Reference: [1] S.
Ranf, Sensing of molecular patterns through cell surface immune receptors.
Curr.
Opin.
Plant Biol.
38, 68–77 (2017).
[2] F.
Boutrot, C.
Zipfel, Function, discovery , and exploitation of plant pattern recognition receptors for broad-spectrum disease resistance.
Annu.
Rev.
Phytopathol.
55, 257–286 (2017).
[3] K.
Kanyuka, JJ Rudd, Cell surface immune receptors: The guardians of the plant's extracellular spaces.
Curr.
Opin.
Plant Biol.
50, 1–8 (2019).
[4] J.
Bigeard, J.
Colcombet, H.
Hirt, Signaling mechanisms in pattern-triggered immunity (PTI).
Mol.
Plant 8, 521–539 (2015).
[5] D.
De Vleesschauwer, G.
Gheysen, M.
Höfte, Hormone defense networking in rice: Tales from a different world.
Trends Plant Sci.
18, 555–565 (2013).
[6 】A.
Robert-Seilaniantz, M.
Grant, JD Jones, Hormone crosstalk in plant disease and defense:More than just jasmonate-salicylate antagonism.
Annu.
Rev.
Phytopathol.
49, 317–343 (2011).
[7] VU Irorere, L.
Tripathi, R.
Marchant, S.
McClean, IM Banat, Microbial rhamnolipid production: A critical re-evaluation of published data and suggested future publication criteria.
Appl.
Microbiol.
Biotechnol.
101, 3941–3951 (2017).
[8] A.
Nickzad, E.
Déziel, The involvement of rhamnolipids in microbial cell adhesion and biofilm development– An approach for control? Lett.
Appl.
Microbiol.
58, 447–453 (2014).
Original link: https:// 3941–3951 (2017).
[8] A.
Nickzad, E.
Déziel, The involvement of rhamnolipids in microbial cell adhesion and biofilm development–An approach for control? Lett.
Appl.
Microbiol.
58, 447–453 (2014 ).
Original link: https:// 3941–3951 (2017).
[8] A.
Nickzad, E.
Déziel, The involvement of rhamnolipids in microbial cell adhesion and biofilm development–An approach for control? Lett.
Appl.
Microbiol.
58, 447–453 (2014 ).
Original link: https://