Selected cell wall-associated components in plant defense responses against microbial pathogens

Role of cell wall-associated kinases in plant development and defense responses

Plant life is coordinated by several developmental and defense associated mechanisms and cell wall is actively important in these mechanisms. The plant cell wall also serves as an important component system that monitors plant growth and defense apart from only protecting the cell. However, resident sensors of the plant cell membrane and pattern recognition receptors (PRRs) also constitute major response mechanisms in plants while they are both as well developed for maintaining cell wall integrity (CWI). These PRRs are molecules such as ligands, peptides or glycans that are released for sensing damage collectively refers to as perceived damage associated molecular patterns (DAMPs), or signals for trigger immunity (TI). Pathogen attack frequently promotes the release of DAMPs, thereby activating TI pathways that contribute to disease resistance. The cell-wall associated kinases (WAKs) are of immense importance in this pathway. WAKs are receptor-like proteins which have their own cytoplasmic protein domain cross-linked with pectin fraction in the plant’s cell wall. They are generally known to take vital roles in cell expansion process but, it is becoming clearer that they are also involved in plant response to environmental stimuli such as pathogen attack, wounding or abiotic stresses. This review highlights the importance of understanding and identifying wall-monitoring systems involving WAKs, CWI sensors, and trigger immunity-associated PRR-DAMP interactions. This will open a new phase of how we can use these components in boosting plant immune functions and in designing better agricultural strategies such as crop breeding for disease resistance.

The role of the cell wall in plant immunity

(microbe-associated molecular pattern) triggered immunity in plants

Plant defence against phytopathogens: Roles of antimicrobial metabolites and breeding strategies for resistance

Among the various phytopathogenic factors affecting plants in their surroundings, fungal pathogens are the worst because they are responsible for the highest number of disease incidences in plants. Almost 8000 phytopathogenic fungal species are known that adversely affect plant metabolism. Due to infection, plants perceive the stress stimulus employing microbe- or damaged-plant-derived molecules, known as elicitors, produced by pathogen attack. After this perception, plants initiate a defensive response against the pathogen by upregulating the synthesis and accumulation of small antimicrobial compounds. To synthesize these compounds, plant must transform their metabolic activities from growth and reproduction to resistance, adaptation and tolerance. This review critically examines the protective strategies employed by plants in response to fungal infection, with a particular focus on the synthesis and accumulation of antimicrobial compounds, such as secondary metabolites (phenols, terpenoids, and alkaloids), pathogenesis-related (PR) proteins (chitinase and β-1,3-glucanase), defence-related phytohormones and enzymatic and non-enzymatic antioxidants. A comprehensive understanding of these metabolites provides plant breeders with valuable insight to identify and select traits linked with enhanced resistance in crop plants. By integrating and upregulating genes engaged in the biogenesis and accumulation of these metabolites, breeders can develop crop varieties with better resilience against fungal pathogens. Such improvements not only lessen dependence on chemical pesticides but also pave the way towards sustainable and ecologically responsible agricultural practices. An illustration features a host plant being attacked by pathogens. A cross-section details the plant cell and plant tissue leading to the nucleus, which branches into five defense responses. On the right, several plant breeding techniques are listed.

Integrin-Linked Kinases 1 and 4 participate in cell-wall-associated immune responses to leaf and root pathogens.

It is proposed that ILKs contribute to pathways connecting elicitor-triggered immune signaling with cell-wall-associated stress responses and that ILK-related defense functions may extend to the cotton root-nematode interaction, while the mechanism remains to be elucidated.

Streptomyces Extracellular Vesicles Promote Plant Defence Responses Through Direct Pathogen Inhibition and Immune Activation.

Extracellular vesicles (EVs) play a critical role in mediating the transfer of bioactive nucleic acids and proteins between plants and pathogens. However, the involvement of EVs in interactions between plants and beneficial bacteria remains poorly understood. In this study, we isolated EVs from Streptomyces violascens DL157, a Gram-positive bacterium with strong antifungal activity, and employed molecular biology, physiological, and multi-omics analyses to investigate the role of DL157 EVs in promoting plant defence responses. The results demonstrated that DL157 EVs can be internalized by plant and fungal cells. DL157 EVs were found to inhibit the germination of fungal spores and enhance plant resistance to both fungal and bacterial pathogens by simultaneously activating salicylic acid- and jasmonic acid-dependent defence pathways. Multi-omics analysis revealed that these EVs are enriched with bioactive metabolites and proteins involved in pathogen inhibition and the induction of plant defence responses. Collectively, our findings offer novel insights into the role of EVs in enhancing plant defence responses by mediating the transfer of bioactive molecules from beneficial bacteria to both phytopathogenic fungi and plant cells.