A β-lactamase Gene of Fusarium oxysporum Alters Rhizosphere Microbiota of Soybean.

The rhizosphere is a multitrophic environment and for soilborne pathogens such as Fusarium oxysporum, microbial competition in the rhizosphere is inevitable before reaching roots for infection. This study established a tritrophic interaction among the plant growth-promoting rhizobacterium Burkholderia ambifaria, F. oxysporum, and soybean to study the effects of F. oxysporum genes on shaping the soybean microbiota. While B. ambifaria inhibited mycelial growth and increased bacterial propagation in the presence of F. oxysporum, F. oxysporum still managed to infect soybean in the presence of B. ambifaria. RNA-Seq identified a putative F. oxysporum secretory β-lactamase-coding gene FOXG_18438 (abbreviated as Fo18438) being up-regulated during soybean infection in the presence of B. ambifaria. The ∆Fo18438 mutants displayed a reduced mycelial growth toward B. ambifaria, and the complementation of full Fo18438 and Fo18438 β-lactamase domain restored mycelial growth. Using the F. oxysporum wild type, ∆Fo18438 mutants, and complemented strains with either full Fo18438, Fo18438 β-lactamase domain, or Fo18438 RTA1-like domain for soil inoculation, 16s RNA amplicon sequencing revealed the abundance of a Burkholderia operational taxonomic unit (OTU) increased in the rhizosphere microbiota infested by strains with Fo18438 β-lactamase domain. Non-metric multidimensional scaling and PICRUSt2 ontology analysis revealed differential abundance of bacterial β-lactam-related function in contrasting the genotypes of F. oxysporum. These results indicated that Fo18438 β-lactamase domain provides F. oxysporum the capability of growing into the soybean rhizosphere, where β-lactam antibiosis is involved in microbial competition. Accordingly, this study highlights the capability of a F. oxysporum gene on altering the soybean rhizosphere and taproot microbiota. Supporting Information.