Role of plant compounds in the modulation of the conjugative transfer of pRet42a

Abstract

One of the most studied mechanisms involved in bacterial evolution and diversification is conjugative transfer (CT) of plasmids. Plasmids able to transfer by CT often encode beneficial traits for bacterial survival under specific environmental conditions. Rhizobium etli CFN42 is a Gram-negative bacterium of agricultural relevance due to its symbiotic association with Phaseolus vulgaris through the formation of Nitrogen-fixing nodules. The genome of R. etli CFN42 consists of one chromosome and six large plasmids. Among these, pRet42a has been identified as a conjugative plasmid. The expression of the transfer genes is regulated by a quorum sensing (QS) system that includes a traI gene, which encodes an acyl-homoserine lactone (AHL) synthase and two transcriptional regulators (TraR and CinR). Recently, we have shown that pRet42a can perform CT on the root surface and inside nodules. The aim of this work was to determine the role of plant-related compounds in the CT of pRet42a. We found that bean root exudates or root and nodule extracts induce the CT of pRet42a in the plant rhizosphere. One possibility is that these compounds are used as nutrients, allowing the bacteria to increase their growth rate and reach the population density leading to the activation of the QS system in a shorter time. We tested if P. vulgaris compounds could substitute the bacterial AHL synthesized by TraI, to activate the conjugation machinery. The results showed that the transfer of pRet42a in the presence of the plant is dependent on the bacterial QS system, which cannot be substituted by plant compounds. Additionally, individual compounds of the plant exudates were evaluated; among these, some increased and others decreased the CT. With these results, we suggest that the plant could participate at different levels to modulate the CT, and that some compounds could be activating genes in the conjugation machinery.

Co-Dependent and Interdigitated: Dual Quorum Sensing Systems Regulate Conjugative Transfer of the Ti Plasmid and the At Megaplasmid in Agrobacterium tumefaciens 15955

“…The observation that even this minimal conjugation is largely abolished in the traI Ti traI At double mutants suggests that quorum sensing is functioning to regulate the process even at its lowest levels. It also is plausible that expression of the traR At gene is regulated by a condition that we have not yet identified such as has been observed in other rhizobia, and under certain conditions might elevate pAt15955 and thereby indirectly pTi15955 conjugation (Banuelos-Vazquez et al 2020).…”

Co-dependent and Interdigitated: Dual Quorum Sensing Systems Regulate Conjugative Transfer of the Ti Plasmid and the At Megaplasmid in Agrobacterium tumefaciens 15955

“…The observation that even this minimal conjugation is largely abolished in the Δ traI Ti Δ traI At double mutants suggests that quorum sensing is functioning to regulate the process even at its lowest levels. It also is plausible that expression of the traR At gene is regulated by a condition that we have not yet identified such as has been observed in other rhizobia, and under certain conditions might elevate pAt15955 and thereby indirectly pTi15955 conjugation (Banuelos-Vazquez et al, 2020 ).…”

RcgA and RcgR, Two Novel Proteins Involved in the Conjugative Transfer of Rhizobial Plasmids

“…In symbiotic bacteria, such as rhizobia, two main mechanisms that regulate CT have been described ( 18 , 19 , 21 – 23 ). The characterization of hypothetical genes by biochemical and molecular biology approaches has allowed for the identification of new actors involved in the described mechanisms ( 28 – 30 , 39 ). In this work, we evaluated the function of three hypothetical genes, and presented evidence of two novel proteins involved in rhizobial plasmid transfer.…”