Root exudate concentrations of indole-3-acetic acid (IAA) and abscisic acid (ABA) affect maize rhizobacterial communities at specific developmental stages.

Root exudates shape the rhizosphere microbiome, but little is known about which specific compounds in root exudates are important. Here we investigated the impacts of the plant-synthesized phytohormones indole-3-acetic acid (IAA) and abscisic acid (ABA) exuded by roots on the maize rhizobacterial communities. To identify maize genotypes that differed in the root exudate concentrations of IAA and ABA we screened hundreds of inbred lines using a semi-hydroponic system. Twelve genotypes with variable exudate concentrations of IAA and ABA were selected for a replicated field experiment. Bulk soil, rhizosphere and root endosphere samples were collected at two vegetative and one reproductive maize developmental stage. IAA and ABA concentration in rhizosphere samples were quantified by LC-MS. The bacterial communities were analyzed by V4 16S rRNA amplicon sequencing. Results indicated that IAA and ABA concentration in root exudates significantly affected the rhizobacterial communities at specific developmental stages. ABA impacted the rhizosphere bacterial communities at later developmental stages, while IAA affected the rhizobacterial communities at the vegetative stages. This study contributed to our knowledge about the influence that specific root exudate compounds have on the rhizobiome composition, showing that the phytohormones IAA and ABA exuded by roots have a role in the plant-microbiome interactions.