beta-Glucosidase facilitates root isoflavone secretion

Plant specialized metabolites (PSMs) are often stored as glycosides in cells and secreted from roots with some chemical modifications. Although isoflavones function as a symbiotic signal with rhizobia and affect the composition of the soybean rhizosphere microbiome, the underlying secretion mechanism from roots is poorly understood. In addition to transporter-mediated secretion, a route through the hydrolysis of isoflavone glycosides in the apoplast by an isoflavone conjugate-hydrolyzing beta-glucosidase (ICHG) is proposed but not yet clarified. We isolated two independent mutants defective in ICHG activity from a soybean high-density mutant library. These mutants were backcrossed to wild-type and their progenies were employed for our analyses. We cultivated homozygous ichg mutants and wild alleles in a field and analyzed transcriptome of leaves and roots, and isoflavone contents in leaves, roots, and rhizosphere soil.