Stereoisomers of Nonvolatile Acetylbutanediol Metabolites Produced by WRN031 Improved Root Elongation of Maize and Rice.

Inoculation of crop plants with strains of beneficial bacteria can result in promotion of plant growth. In our study, we demonstrated that WRN031 as a plant-growth-promoting rhizobacteria (PGPR) improved the maize seedling growth following inoculation with WRN031. Fluorescence microscopy visualization indicated that GFP-labeled WRN031 had accumulated on the maturation zones of both primary and lateral roots of maize. Two metabolites were detected in the rhizosphere soil of maize root inoculation with WRN031 using HPLC-DAD analyses. Through guided isolation from an ethyl acetate extract of WRN031, these two nonvolatile stereoisomers 3,4-acetylbutanediol (3,4-ABD, ) and 3,4-acetylbutanediol (3,4-ABD, ) were identified and found to occur at a ratio of 1:2 (v/v) in maize rhizosphere soil. Bioactivity screening indicated that compounds and , as well as a v/v = 1:2 mixture of both and , significantly improved the root elongation of both maize and rice, with the effective enhancement concentration related to their concentration in rhizosphere soil. These results suggested that 3,4-ABD and 3,4-ABD produced by WRN031 might improve the growth of their host plants and provides evidence that nonvolatiles accumulating in the root maturation zone may regulate the relationship between roots and beneficial bacteria.