Natural Variation of Immune Markers Reveals Internal Bacterial Conflict

Jenn Hoskins
31st May, 2024

Natural Variation of Immune Markers Reveals Internal Bacterial Conflict

The non-immunogenic CspB protein from Clavibacter is conserved across species and highly expressed (a, b), enabling it to function as an intrabacterial antagonist by suppressing the immune response triggered by immunogenic CSPs from both its own genome and other bacteria (dā€“f).

Image adapted from: Stevens et al. / CC BY (Source)

Key Findings

  • The study from the University of California, Davis, explored how plants detect and respond to pathogens by examining immune responses to MAMPs in Arabidopsis and tomato
  • Researchers found that the sequence and copy number of MAMP epitopes significantly influence immune perception in plants
  • The study revealed a mechanism called intrabacterial antagonism, where nonimmunogenic forms of proteins block the perception of immunogenic forms, helping pathogens evade plant immune systems
Understanding how plants and animals detect and respond to pathogens is essential for improving agricultural production and disease resistance. A recent study from the University of California, Davis, delved into the complexity of immune induction by characterizing the epitope landscape of five proteinaceous microbe-associated molecular patterns (MAMPs) across 4,228 plant-associated bacterial genomes[1]. MAMPs are biomolecules that trigger immune responses in plants and animals. The study's primary goal was to understand how different MAMP epitopes (specific parts of the molecule recognized by the immune system) and their variations influence immune induction. This is crucial because agricultural production is frequently hampered by pathogens, and transferring immune receptors could be a potential solution. The researchers found that despite the diversity of MAMPs, their natural variation was limited and experimentally testable. They examined immune responses in two plant models, Arabidopsis and tomato, and discovered that both the sequence and copy number of MAMP epitopes played significant roles in immune perception. For instance, Elongation Factor Tu, a common bacterial protein, is mostly found as a single copy in bacterial genomes, with 92% of its epitopes being immunogenic (capable of inducing an immune response). On the other hand, cold shock proteins are present in multiple copies in 99.9% of bacterial genomes, and 46% of these copies are nonimmunogenic (unable to induce an immune response). Interestingly, the study uncovered a mechanism of immune evasion called intrabacterial antagonism. This occurs when a nonimmunogenic form of a cold shock protein blocks the perception of immunogenic forms within the same genome. This finding highlights the complexity of pathogen-host interactions and suggests that pathogens can evolve mechanisms to evade plant immune systems. This study builds on previous research that explored the role of MAMPs and other molecular patterns in plant immunity. For example, earlier studies have shown that eicosapolyenoic fatty acids, such as arachidonic acid (AA) and eicosapentaenoic acid, can act as MAMPs to induce disease resistance in plants[2]. These fatty acids are strong elicitors of immune responses in solanaceous plants and have bioactivity in other plant families. The research also demonstrated that extracts from the brown seaweed Ascophyllum nodosum, which is rich in eicosapolyenoic fatty acids, can induce disease resistance in plants[2]. Furthermore, the study aligns with the broader understanding of plant immune systems, which involve a two-tiered innate immune detection-and-response system[3]. The first tier involves pattern recognition receptors (PRRs) that detect MAMPs and trigger pattern-triggered immunity (PTI). The second tier involves nucleotide-binding leucine-rich repeat receptors (NLRs) that detect specific pathogen effectors and trigger a more robust immune response. The interplay between PRR- and NLR-mediated immunity is crucial for a comprehensive defense against pathogens[3]. The findings from the University of California, Davis, add a new layer of understanding to how plants perceive and respond to diverse MAMPs. By characterizing the epitope landscape and identifying mechanisms of immune evasion, the study provides valuable insights for deploying and engineering immune receptors based on natural variation. This could pave the way for developing crops with enhanced resistance to a broad spectrum of pathogens, ultimately improving agricultural productivity and sustainability.

MedicineGeneticsBiochem

References

Main Study

1) Natural variation of immune epitopes reveals intrabacterial antagonism.

Published 4th June, 2024 (future Journal edition)

https://doi.org/10.1073/pnas.2319499121

Related Studies

2) Overlapping Local and Systemic Defense Induced by an Oomycete Fatty Acid MAMP and Brown Seaweed Extract in Tomato.

https://doi.org/10.1094/MPMI-09-22-0192-R

3) Thirty years of resistance: Zig-zag through the plant immune system.

https://doi.org/10.1093/plcell/koac041


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