The Metabolic Response of Brachypodium Roots to the Interaction with Beneficial Bacteria Is Affected by the Plant Nutritional Status.

Martino Schillaci,Cheka Kehelpannala,Penelope M C Smith,Federico Martinez-Seidel,Michelle Watt,Borjana Arsova,Ute Roessner

doi:10.3390/metabo11060358

Abstract

The potential of plant growth promoting (PGP) bacteria in improving the performance of plants in suboptimal environments is increasingly acknowledged, but little information is available on the mechanisms underlying this interaction, particularly when plants are subjected to a combination of stresses. In this study, we investigated the effects of the inoculation with the PGP bacteria Azospirillum brasilense (Azospirillum) on the metabolism of the model cereal Brachypodium distachyon (Brachypodium) grown at low temperatures and supplied with insufficient phosphorus. Investigating polar metabolite and lipid fluctuations during early plant development, we found that the bacteria initially elicited a defense response in Brachypodium roots, while at later stages Azospirillum reduced the stress caused by phosphorus deficiency and improved root development of inoculated plants, particularly by stimulating the growth of branch roots. We propose that the interaction of the plant with Azospirillum was influenced by its nutritional status: bacteria were sensed as pathogens while plants were still phosphorus sufficient, but the interaction became increasingly beneficial for the plants as their phosphorus levels decreased. Our results provide new insights on the dynamics of the cereal-PGP bacteria interaction, and contribute to our understanding of the role of beneficial microorganisms in the growth of cereal crops in suboptimal environments.

Highlights

Low temperature and P deficiency are two of the most common abiotic stresses for crops, and their combination can be detrimental during the early stages of the development of winter cereals in P-poor regions of the world [1].Low temperature affects virtually all metabolic processes of plants by changing the enzyme kinetics of biochemical reactions, inhibiting photosynthesis, damaging intra- and intercellular structures, decreasing water and nutrient uptake capacity, and causing oxidative stress [2,3]
The comparison of polar metabolites and lipids extracted from the roots of Azospirilluminoculated and non-inoculated roots of Brachypodium at 7, 14, and 21 days after the inoculation (DAI) revealed that the time of the harvest was a strong discriminant between samples, while the bacterial treatment affected specific sections of root metabolism at different time points
During the early stages of the experiment, we hypothesize that bacteria were sensed as pathogens by the host, and Brachypodium produced polar compounds with antimicrobial properties in order to limit the bacterial colonization of roots

Summary

Introduction

Low temperature and P deficiency are two of the most common abiotic stresses for crops, and their combination can be detrimental during the early stages of the development of winter cereals in P-poor regions of the world [1]. Low temperature affects virtually all metabolic processes of plants by changing the enzyme kinetics of biochemical reactions, inhibiting photosynthesis, damaging intra- and intercellular structures, decreasing water and nutrient uptake capacity, and causing oxidative stress [2,3]. Plants use P in most of their metabolic reactions, and phosphate deficiency activates various metabolic rearrangements, which increase external inorganic P (Pi) uptake and optimize internal Pi use efficiency [4]. Low temperatures can affect plant metabolic responses to low P availability and vice versa. By decreasing plant growth rate, low temperature might indirectly affect plant P requirements; these stresses have an opposite effect on root development—

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