An investigation of the tri-trophic interactions in the rhizosphere of Medicago truncatula using a functional microbiome approach

Abstract

The use of plant beneficial organisms derived from the plant microbiome (i.e. biologicals), is gaining interest in agriculture as a solution to decrease dependence on pesticide and fertilizer use. It is understood that the application of individual plant growth promoting rhizobacteria (PGPR) increases plant health. However, limited research efforts have investigated complex interactions occurring between multiple species of beneficial bacteria, and how the outcomes of those associations influence their ability to benefit the plant. There currently is little research into the specific types of rhizosphere interspecies signaling communication that may affect how plant beneficial bacteria perform. Using a tri-trophic model system of the legume Medicago truncatula A17 Jemalong, its mutualistic symbiont Sinorhizobium meliloti strain Rm8530 (hereafter Rm8530), and the PGPR Bacillus subtilis UD1022 (hereafter UD1022), we show that interactions between the PGPRs may influence their individual associations and activities on the plant root. Expression and functional analysis of Rm8530 suggest that UD1022 produces extracellular compounds that impact the components involved in the Rm8530 quorum sensing (QS) system. At the same time, Rm8530 may be influencing the functional plant association strategies of UD1022. This interaction could have greater implications in altering the ability of the PGPRs to positively affect plant health.