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Microbial small molecules – weapons of plant subversion

Ronnie de Jonge: Plant-Microbe Interactions, Department of Biology, Faculty of Science, Utrecht University

<div>Plants live in close association with myriads of microbes in nature. Most of these interactions are harmless, but a multitude of pathogenic microbes can cause severe disease and therefore impact plant health. In the case of crop plants, plant diseases often reduce yield and quality while endangering food security. Beneficial microbes, unlike their pathogenic counterparts, provide plants with important services such as enhanced nutrient uptake and protection against pathogenic ones. Like plant pathogens, beneficial microbes may modulate host immunity to efficiently colonize the nutrient-rich niches found within and around the roots and aerial tissues of a plant, a situation roughly analogous to the establishment of commensal gut microbes in human. Various mechanisms have been described by which pathogenic and symbiotic microbes communicate with their host, including the delivery of effector proteins through dedicated secretion machineries and the production of phytohormones, toxins and other small molecules. Plants on the other hand attract and signal to their associated microbes via exudation of photosynthetically fixed carbon sources, quorum-sensing mimicry molecules and selective compounds such as the strigolactones and flavonoids. Plant - microbe communication by means of exchanging signalling compounds thus forms an integral part of the establishment of both beneficial and pathogenic interactions. In parallel with microbe – microbe communication, plant – microbe communication shapes plant-associated microbial communities both within and around the plant. Here we discuss large-scale genome comparisons of small molecule biosynthesis capabilities within the <em>Pseudomonas </em>genus, and highlight the vast and diverse biosynthetic potential of individual microbial genomes and the population as a whole.</div>