The lactonase BxdA mediates metabolic adaptation of maize root bacteria to benzoxazinoids

Root exudates contain secondary metabolites that affect the plant’s root microbiome. How microbes cope with these bioactive compounds, and how this ability shapes root microbiomes remain largely unknown. We investigated how maize root bacteria metabolise benzoxazinoids, the main specialised metabolites of maize. Diverse and abundant bacteria metabolised the major compound (6-methoxy-benzoxazolin-2-one, MBOA) in the maize rhizosphere to 2-amino-7-methoxyphenoxazin-3-one (AMPO). By contrast, bacteria isolated from Arabidopsis, which does not produce benzoxazinoids, were unable to metabolise MBOA. Among Microbacteria strains, this differential metabolisation allowed to identify a conserved gene cluster containing the lactonase bxdA. BxdA converts MBOA to AMPO in vitro and we show that this capacity provided bacteria a growth benefit under carbon-limiting conditions. Together these results reveal that maize root bacteria - through BxdA - are metabolically adapted to the benzoxazinoids of their host. We propose that metabolic adaptation to plant-specialised compounds shapes root bacterial communities across the plant kingdom.