Auxin secretion by Bacillus amyloliquefaciens FZB42 both stimulates root exudation and limits phosphorus uptake in Triticum aestivium.

Peter J Talboys,Darren W Owen,John R Healey,David L Jones,Paul J A Withers

doi:10.1186/1471-2229-14-51

Abstract

BackgroundThe use of auxin-producing rhizosphere bacteria as agricultural products promises increased root production and therefore greater phosphate (Pi) uptake. Whilst such bacteria promote root production in vitro, the nature of the bacteria-plant interaction in live soil, particularly concerning any effects on nutrient uptake, are not known. This study uses Bacillus amyloliquefaciens FZB42, an auxin-producing rhizobacterium, as a dressing on Triticum aestivum seeds. It then examines the effects on root production, Pi uptake, Pi-related gene expression and organic carbon (C) exudation.ResultsSeed treatment with B. amyloliquefaciens FZB42 increased root production at low environmental Pi concentrations, but significantly repressed root Pi uptake. This coincided with an auxin-mediated reduction in expression of the Pi transporters TaPHT1.8 and TaPHT1.10. Applied exogenous auxin also triggered an increase in root C exudation. At high external Pi concentrations, root production was promoted by B. amyloliquefaciens FZB42, but Pi uptake was unaffected.ConclusionsWe conclude that, alongside promoting root production, auxin biosynthesis by B. amyloliquefaciens FZB42 both re-models Pi transporter expression and elevates organic C exudation. This shows the potential importance of rhizobacterial-derived auxin following colonisation of root surfaces, and the nature of this bacteria-plant interaction in soil.

Highlights

The use of auxin-producing rhizosphere bacteria as agricultural products promises increased root production and greater phosphate (Pi) uptake
This study aims to assess the nature of the biological interaction between B. amyloliquefaciens FZB42 and the Triticum aestivum root system: with the hypothesis that any effects of B. amyloliquefaciens FZB42 colonisation on root Pi uptake rates are dependent upon the soil Pi concentration
Soil-grown, T. aestivum root systems were grown in soil with either a high or low exogenous Pi supply: it was found that B. amyloliquefaciens FZB42 seed-treatment resulted in a reduced Pi uptake rate under low external Pi conditions compared with the uninoculated controls (Figure 2A)

Summary

Introduction

The use of auxin-producing rhizosphere bacteria as agricultural products promises increased root production and greater phosphate (Pi) uptake. Whilst such bacteria promote root production in vitro, the nature of the bacteria-plant interaction in live soil, concerning any effects on nutrient uptake, are not known. This study uses Bacillus amyloliquefaciens FZB42, an auxin-producing rhizobacterium, as a dressing on Triticum aestivum seeds. It examines the effects on root production, Pi uptake, Pi-related gene expression and organic carbon (C) exudation. This study focuses on the auxinproducing bacterium Bacillus amyloliquefaciens FZB42, and the nature of the resulting plant-microbe interactions involved in plant P uptake

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