Abstract
Auxin is a key phytohormone that is integral to plant developmental processes including those underlying root initiation, elongation, and branching. Beneficial microbes have been shown to have an impact on root development, potentially mediated through auxin. In this study, we explore the role of host auxin signaling and transport components in mediating the root growth promoting effects of beneficial microbes. Towards this end, we undertook co-culture studies of Arabidopsis thaliana plants with microbes previously reported to promote lateral root proliferation and produce auxin. Two types of beneficial microbes were included in the present study; a plant growth promoting bacterial species of interest, Pseudomonas fluorescens GM30, and a well-studied plant growth promoting fungal species, Serendipita indica (Piriformospora indica). Following co-culture, lateral root production was found restored in auxin transport inhibitor-treated plants, suggesting involvement of microbe and/or microbially-produced auxin in altering plant auxin levels. In order to clarify the role of host auxin signaling and transport pathways in mediating interactions with bacterial and fungal species, we employed a suite of auxin genetic mutants as hosts in co-culture screens. Our result show that the transport proteins PIN2, PIN3, and PIN7 and the signaling protein ARF19, are required for mediating root architecture effects by the bacterial and/or fungal species. Mutants corresponding to these proteins did not significantly respond to co-culture treatment and did not show increases in lateral root production and lateral root density. These results implicate the importance of host auxin signaling in both bacterial and fungal induced changes in root architecture and serve as a driver for future research on understanding the role of auxin-dependent and auxin-independent pathways in mediating plant-microbe interactions in economically important crop species.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan(http://energy.gov/downloads/doe-public-access-plan).
