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Microbes are single or multicellular microscopic organisms. Plant-microbe interactions can bring benefit or harm to plants. For instance, mycorrhizal fungi can supply plants with nutrients, whereas fungal, bacterial and viral pathogens can impair plant function.
Plants evolved NLR sensors to detect bacterial effectors or their activity. A genetic analysis in Arabidopsis expands the role of the ZAR1 NLR protein. ZAR1 recognizes effector HopF2a through its association with pseudokinase ZRK3, inducing resistance without hypersensitive response.
Small RNAs regulate plant–pathogen interactions. In rice, AGO18 sequesters microRNA528, which negatively regulates resistance to viruses through the silencing of L-ascorbate oxidase and thus controls the production of reactive oxygen species.
Many plants detect bacteria by the receptor FLS2 that binds the flagellin epitope flg22. A new pattern recognition receptor FLS3 in tomato detects flagellin from a second side; a further move in the evolutionary game of ‘hide and seek’ where pathogens evade recognition and hosts evolve novel immunoreceptors to detect them.