Benzoic Acid Secreted From the Chickpea Root Promotes Persistent Colonisation by Specific Soil Microbes

The plant root tip is highly sensitive to environmental cues and exerts sensory, chemical and movement responses. However, the microbial diversification at the root tip, and the nature of root-selection for microbes, are poorly understood. This study investigated root exudation and microbiome colonisation in the chickpea (Cicer arietinum L.) root tip and root base, in diverse soils. For the endosphere microbiome, deterministic effects were more important than stochastic processes in shaping the root tip microbiome, indicated by the stable endophyte composition independent of the soil microbiota background. A genotype with high secretion of benzoic acid (BA), was consistently colonised by 3 core ASV (Amplicon Sequence Variant) from the Burkholderia clade. Two of 98 isolated strains were confirmed as the culturable candidates of the core ASV, both of which were characterised by superior BA tolerance and the ability to utilise BA as a sole carbon source, demonstrated through high expression of BA degradation genes. Additionally, one IAA-producing coloniser specifically promoted the growth of its original host genotype across different soils, but provided no consistent benefits for other genotypes. Our results reveal the mechanisms by which soil microbes interact with root exudates of a host genotype to establish colonisation.