Therefore, the apparent host promiscuity of some microorganisms, such as pseudomonads, raises questions on the metabolic changes required of bacteria to colonize multiple hosts or to maintain an association with a host that undergoes physiological changes. There is growing recognition that plant species select for distinctive microbial communities 7, with more phylogenetically distant plant hosts recruiting the most distinct microbiota populations 8. However, certain pseudomonads have proven to be effective as biocontrol agents on plant species different from that of their origin or on multiple crops, suggesting that pseudomonads are rather promiscuous colonists of plants 6. ![]() There are no comprehensive studies of the phylogenetic breadth of plants that a given Pseudomonas strain can colonize. Many plant-associated strains facilitate plant growth, alleviate abiotic stress, or protect plants against pathogens 5. Their competitive edge involves metabolic flexibility and producing a wide range of secondary metabolites, including antimicrobials and iron-scavenging compounds 4. Pseudomonas bacteria can thrive in various environmental niches, including the roots of various plant hosts. Differences in the composition of exudates and the workings of the plant's innate immunity shape the composition and the activity of the root microbiota 3. The exact chemical composition of exudates depends on the plant species and the plant's physiological status, the latter dependent on the developmental stage, nutrient availability, and the presence of stressors 2. Root exudates contain primary metabolites such as organic acids, amino acids, sugars and secondary metabolites with bioactive or signalling properties. Plants nourish microbial communities in the rhizosphere by releasing blends of organic compounds through the roots 1. Our results provide directions to explore mechanisms of host adaptation in plant-associated microorganisms. ![]() The shared response to exudates seemed to be affected both by compounds originating from the plants and those from their growth environment: arsenic resistance and bacterioferritin synthesis were upregulated, while sulfur assimilation, sensing of ferric citrate and/or other iron carriers, heme acquisition, and transport of polar amino acids were downregulated. Genes associated with motility were induced by maize but repressed by tomato. Maize specifically induced the activity of Me圎 RND-type efflux pump and copper tolerance. The first two indicate the presence of NO donors in the exudates of the test plants. ![]() Pathways upregulated only by tomato exudates included nitric oxide detoxification, repair of iron-sulfur clusters, respiration through the cyanide-insensitive cytochrome bd, and catabolism of amino and/or fatty acids. Our main goal was to identify the differences and the common points between these two responses. Here, we addressed this knowledge gap by employing RNAseq and comparing transcriptomic responses of Pseudomonas donghuensis P482 to root exudates of two plant hosts: tomato and maize. However, the metabolic adaptations required for host promiscuity are unknown. Pseudomonads are metabolically flexible and can thrive on different plant hosts.
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