Argonaute Proteins: Why Are They So Important for the Legume-Rhizobia Symbiosis?

Oswaldo Valdés-López,Maria Del Socorro Sánchez-Correa,Mariel C Isidra-Arellano,Maria Del Rocio Reyero-Saavedra,Damien Formey,Tadeo F Fernandez-Göbel

doi:10.3389/fpls.2019.01177

Oswaldo Valdés-López, Maria Del Socorro Sánchez-Correa + Show 4 more

Open Access

https://doi.org/10.3389/fpls.2019.01177

Copy DOI

Abstract

Unlike most other land plants, legumes can fulfill their nitrogen needs through the establishment of symbioses with nitrogen-fixing soil bacteria (rhizobia). Through this symbiosis, fixed nitrogen is incorporated into the food chain. Because of this ecological relevance, the genetic mechanisms underlying the establishment of the legume–rhizobia symbiosis (LRS) have been extensively studied over the past decades. During this time, different types of regulators of this symbiosis have been discovered and characterized. A growing number of studies have demonstrated the participation of different types of small RNAs, including microRNAs, in the different stages of this symbiosis. The involvement of small RNAs also indicates that Argonaute (AGO) proteins participate in the regulation of the LRS. However, despite this obvious role, the relevance of AGO proteins in the LRS has been overlooked and understudied. Here, we discuss and hypothesize the likely participation of AGO proteins in the regulation of the different steps that enable the establishment of the LRS. We also briefly review and discuss whether rhizobial symbiosis induces DNA damages in the legume host. Understanding the different levels of LRS regulation could lead to the development of improved nitrogen fixation efficiency to enhance sustainable agriculture, thereby reducing dependence on inorganic fertilizers.

Highlights

The symbiosis between legumes and rhizobia is of considerable ecological importance because through it, fixed nitrogen is incorporated into the food chain (Castro-Guerrero et al, 2016)
We recently reported that AGO5 participates in the rhizobial infection process in both Phaseolus vulgaris and Glycine max (Reyero-Saavedra et al, 2017)
Because AGO2 and AGO3 members are difficult to distinguish in legumes, due to the phylogenetically clustering of the two members by species of origin and not by member type (Zhang et al, 2015), here we focus on the “AGO2/3” group and AGO7 (Figure 2)

Summary

Introduction

The symbiosis between legumes and rhizobia is of considerable ecological importance because through it, fixed nitrogen (e.g., ammonium) is incorporated into the food chain (Castro-Guerrero et al, 2016). As symbiotic nitrogen fixation plays essential roles in soil function, nutrient and water cycling, and food security, its exploitation and improvement in crop plants can promote lower input sustainable agriculture (Ferguson et al, 2019a). To establish this symbiosis, a molecular dialogue between legumes and rhizobia is required (Venkateshwaran et al, 2013).

Objectives

Conclusion