Plant-Microbe Interaction Defense Mechanisms in Early-Diverging Land Plants

Early-diverging land plants, including bryophytes such as mosses, liverworts and hornworts, occupy a pivotal position in the evolution of terrestrial flora and their defence against microbial foes. These non-vascular lineages deploy an array of innate immune responses that share core features with flowering plants yet also exhibit lineage-specific innovations. At the cell surface, pattern recognition receptors perceive conserved microbial signatures and activate rapid signal transduction cascades typified by mitogen-activated protein kinases. Downstream responses include reinforcement of the cell wall through callose and phenolic deposition, generation of reactive oxygen species and accumulation of defence hormones. In many cases, an orchestrated hypersensitive-like cell death limits pathogen spread. Intracellular resistance revolves around nucleotide-binding leucine-rich repeat receptors that detect effector molecules and amplify defence outputs. Comparative genomics reveals that bryophytes possess orthologues of key immune components, while also harbouring unique enzymes and metabolic routes, some acquired by horizontal gene transfer, which afford novel biochemical defences. The study of these primitive lineages not only illuminates the dawn of land plant immunity but may yield untapped reservoirs of resistance traits, informing the engineering of durable disease tolerance in crop species.

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Technical terms

Bryophytes: Non-vascular land plants including mosses, liverworts and hornworts.

Pattern recognition receptors (PRRs): Cell-surface proteins that detect conserved microbial molecules.

Pattern-triggered immunity (PTI): Innate defence initiated by PRR activation.

Nucleotide-binding leucine-rich repeat receptors (NLRs): Intracellular receptors recognising pathogen effectors.

Effector-triggered immunity (ETI): Robust defence response following NLR recognition of pathogen effectors.

Reactive oxygen species (ROS): Chemically reactive molecules generated during defence, contributing to cell wall fortification and signalling.

Hypersensitive response (HR): Localised programmed cell death that restricts pathogen spread.

References

1. Immunobiodiversity: Conserved and specific immunity across land plants and beyond. Molecular Plant (2023).
2. An Overview of PRR- and NLR-Mediated Immunities: Conserved Signaling Components across the Plant Kingdom That Communicate Both Pathways. International Journal of Molecular Sciences (2022).
3. Physcomitrium patens Infection by Colletotrichum gloeosporioides: Understanding the Fungal–Bryophyte Interaction by Microscopy, Phenomics and RNA Sequencing. Journal of Fungi (2021).