Effects Of Root Exudates On Arabidopsis Rhizosphere Microbes

Plant root exudates,especially secondary metabolites produced or increased in specific environments,make an important contribution to plant health.As mediators of communication between plants and rhizosphere microorganisms,root exudates usually perform functions such as providing ecological niches for beneficial bacteria or suppressing pathogenic bacteria.However,their interactions with the rhizosphere microbiome remain cryptic,and current studies on them are mainly limited to the effects of a few compounds on a small number of microorganisms,and high-throughput studies are lacking.Here,we summarized key classes of secondary metabolites across species,including flavonoids,alkaloids,coumarins,lignins total of 54 root exudates,and systematically investigated their interactions with 79 rhizosphere bacteria.First,we qualitatively investigated the regulatory effects of these 54 compounds on the growth of selected bacteria.Among 4266 combinations,we found 445 combinations in which the compounds inhibited microbial growth,only 23 combinations in which the compounds promoted microbial growth,and 3798 combinations with no regulatory effect.Among the growth-promoting combinations,11 compounds promoted the growth of at least one species,and the best promoting compound was juglone,which could promote the growth of eight species.Forty-nine compounds in the growthinhibiting combinations inhibited the growth of at least one species,and the most effective inhibitory compound was 8-hydroxyquinoline,which could inhibit up to 57 species,accounting for 72%.Due to its significant inhibitory effect,we quantified the degradation ability of the inter-rhizosphere microbiome by LC-MS and found that several bacteria,including members of the genus Pseudomonas,were able to effectively degrade 8-hydroxyquinoline.Subsequently,we compared the two major quinoline oxidase genes,Qor MSL and Qox LMS,reported in the literature in the genomes of all degrading bacteria and found that the majority of degrading bacteria had proteins similar to both.Among them,the 4632 gene of Aminobacter sp.Root100 achieved 58%sequence identity with the L subunit directly related to quinoline degradation,and the4633 and 4634 genes also achieved 35% and 48% sequence identity,respectively.In addition,we made reasonable speculations on the structures of possible quinoline metabolites detected by LC-MS to lay the foundation for further experiments to characterize the activity of selected degradation enzymes,which can correlate genomic information with inter-root chemistry to some extent.In conclusion,we systematically characterized the growth-regulating effects of root exudates on rhizosphere bacteria,demonstrating their universality and selection specificity,as well as the great variability in the microbial response and metabolic capacity to these compounds.This not only deepens our understanding of the hostmicrobe ecological framework mediated by small molecule compounds,but also provides some basis for personalized strategies to improve the microbiome of crops in agricultural production.