Signaling peptides control beneficial and pathogenic plant-microbe interactions.

Interactions between organisms, such as those between plants and microbes, require extensive signaling between and within each organism to detect and recognize the partner and elicit an appropriate response. Multiple families of small signaling peptides regulate plant interactions with beneficial or pathogenic microbes, and sometimes both. Some of these signaling peptides transmit information between different cells or organs of the host and allow plants to orchestrate a coordinated response towards microbial mutualists or pathogens. However, not only plants produce signaling peptides required for the interactions. Microbes themselves also secrete peptide signals, which are detected by host receptors and required for infection. Among these are microbial peptides mimicking those of plants, allowing mutualistic or pathogenic microbes to hijack endogenous plant signaling pathways and evade the host immune system. In this review, we provide a comprehensive summary of current knowledge on host- and microbe-derived signaling peptides and their cognate receptors regulating mutualistic and parasitic plant-microbe interactions. Furthermore, we describe how microbes hijack endogenous host signaling pathways, and discuss possible crosstalk between the plant signaling pathways controlling mutualism with those modulating immune responses to pathogens.