The Presence of Plant-Associated Bacteria Alters Responses to N-acyl Homoserine Lactone Quorum Sensing Signals that Modulate Nodulation in Medicago Truncatula.

Debora F Veliz-Vallejos,Ulrike Mathesius,Akitomo Kawasaki

doi:10.3390/plants9060777

Abstract

Bacteria use quorum sensing signaling for cell-to-cell communication, which is also important for their interactions with plant hosts. Quorum sensing via N-acyl-homoserine lactones (AHLs) is important for successful symbioses between legumes and nitrogen-fixing rhizobia. Previous studies have shown that plant hosts can recognize and respond to AHLs. Here, we tested whether the response of the model legume Medicago truncatula to AHLs from its symbiont and other bacteria could be modulated by the abundance and composition of plant-associated microbial communities. Temporary antibiotic treatment of the seeds removed the majority of bacterial taxa associated with M. truncatula roots and significantly altered the effect of AHLs on nodule numbers, but lateral root density, biomass, and root length responses were much less affected. The AHL 3-oxo-C14-HSL (homoserine lactone) specifically increased nodule numbers but only after the treatment of seeds with antibiotics. This increase was associated with increased expression of the early nodulation genes RIP1 and ENOD11 at 24 h after infection. A 454 pyrosequencing analysis of the plant-associated bacteria showed that antibiotic treatment had the biggest effect on bacterial community composition. However, we also found distinct effects of 3-oxo-C14-HSL on the abundance of specific bacterial taxa. Our results revealed a complex interaction between plants and their associated microbiome that could modify plant responses to AHLs.

Highlights

Plant-associated bacteria can have beneficial effects on plant performance, for example, by altering plant growth and development or by inducing tolerance to diverse biotic and abiotic stresses [1,2,3]
Many plant-associated bacteria use cell-to-cell signaling via quorum sensing signals to coordinate behaviors that support successful colonization or invasion of plant hosts [7,8]
We focused on the acyl-homoserine lactones (AHLs) 3-oxo-C14 -HSL

Summary

Introduction

Plant-associated bacteria can have beneficial effects on plant performance, for example, by altering plant growth and development or by inducing tolerance to diverse biotic and abiotic stresses [1,2,3]. Bacterial and fungal species can colonize all parts of the plant, including surfaces and the apoplast of roots, shoots, and seeds. Plants can be colonized by various bacteria during different developmental stages and can inherit some of their bacterial consortia via seeds in a process called vertical transmission. The seed-borne bacterial community structure is able to disperse systemically throughout the plant, colonizing roots and nodules [5,6]. Many plant-associated bacteria use cell-to-cell signaling via quorum sensing signals to coordinate behaviors that support successful colonization or invasion of plant hosts [7,8]. Gram-negative bacteria typically use acyl-homoserine lactone (AHL) signals, which control behaviors important for Plants 2020, 9, 777; doi:10.3390/plants9060777 www.mdpi.com/journal/plants

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