Plant–microbe interactions: organelles and the cytoskeleton in action

Abstract

Contents Summary1012I.Introduction1012II.The endomembrane system in plant–microbe interactions1013III.The cytoskeleton in plant–microbe interactions1017IV.Organelles in plant–microbe interactions1019V.Inter‐organellar communication in plant–microbe interactions1022VI.Conclusions and prospects1023Acknowledgements1024References1024 Summary Plants have evolved a multilayered immune system with well‐orchestrated defense strategies against pathogen attack. Multiple immune signaling pathways, coordinated by several subcellular compartments and interactions between these compartments, play important roles in a successful immune response. Pathogens use various strategies to either directly attack the plant's immune system or to indirectly manipulate the physiological status of the plant to inhibit an immune response. Microscopy‐based approaches have allowed the direct visualization of membrane trafficking events, cytoskeleton reorganization, subcellular dynamics and inter‐organellar communication during the immune response. Here, we discuss the contributions of organelles and the cytoskeleton to the plant's defense response against microbial pathogens, as well as the mechanisms used by pathogens to target these compartments to overcome the plant's defense barrier.

Chloroplasts and Plant Immunity: Where Are the Fungal Effectors?

“…In the context of disease, lesion mimic mutants in plants form spontaneous lesions that resemble HR, and some of these mutations are in nuclear genes that encode chloroplast proteins [20]. Retrograde signaling is thought to involve Ca 2+ sensing and a ROS signal that could be transferred to the nucleus via stromule bridges originating from the chloroplasts and observed during pathogen attacks [4][5][6]8,10,17,[21][22][23][24][25]. Stromules are stroma-filled, tube-like extrusions originating from the chloroplast [21][22][23][24][25].…”

“…Retrograde signaling is thought to involve Ca 2+ sensing and a ROS signal that could be transferred to the nucleus via stromule bridges originating from the chloroplasts and observed during pathogen attacks [4][5][6]8,10,17,[21][22][23][24][25]. Stromules are stroma-filled, tube-like extrusions originating from the chloroplast [21][22][23][24][25]. They depend on the chloroplast unusual positioning 1 protein (CHUP1) that promotes stromule formation along microtubule-guided extensions, with actin microfilaments providing anchoring points [21][22][23][24][25].…”

“…Stromules are stroma-filled, tube-like extrusions originating from the chloroplast [21][22][23][24][25]. They depend on the chloroplast unusual positioning 1 protein (CHUP1) that promotes stromule formation along microtubule-guided extensions, with actin microfilaments providing anchoring points [21][22][23][24][25]. Ca 2+ fluxes are induced during pathogen recognition and include Ca 2+ spikes in the chloroplast after PTI is triggered by flagellin or chitin.…”

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“…These exosomes could play a role in the direct delivery of antimicrobial compounds, or deliver RNA molecules that modulate defense signaling pathways or regulate cell-to-cell communication. 20 Finally, distributed at PM level, there are receptors, named transmembrane pattern recognition receptors (PRRs) that have a 'function TLRs-like' (in animals) and that recognize pathogen associated molecular patterns (PAMPs), such as bacterial flagellin or fungal chitin or danger associated molecular patterns (DAMPs). This type of immune response is called PAMPtriggered immunity (PTI) 19,20 and frequently it is strong enough against most pathogens to avoid infection.…”

“…20 Finally, distributed at PM level, there are receptors, named transmembrane pattern recognition receptors (PRRs) that have a 'function TLRs-like' (in animals) and that recognize pathogen associated molecular patterns (PAMPs), such as bacterial flagellin or fungal chitin or danger associated molecular patterns (DAMPs). This type of immune response is called PAMPtriggered immunity (PTI) 19,20 and frequently it is strong enough against most pathogens to avoid infection. Once there has been the binding between PAMPs/DAMPs and PRRs, the plant immune processes continue with the endocytosis of the pattern recognition receptors and their intracellular trafficking up till destruction.…”