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

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.

Broad-scale phenotyping in Arabidopsis reveals varied involvement of RNA interference across diverse plant-microbe interactions

“…Soybean AGO1 plays a positive role in the bacterial Sinorhizobium root-nodule symbiosis via ckRNAi (Ren et al, 2019). Furthermore, AGO1 has been speculated to regulate fungal symbiosis, supported by the prediction of plant mRNA targets of fungal sRNAs accumulating in the symbiosis between beneficial microorganisms and their hosts (Silvestri et al, 2019; Valdés-López et al, 2019; Wong-Bajracharya et al, 2022). Therefore, we next carried out colonization experiments with the mutualist basidiomycete S. indica , revealing AGO4 downregulation at late time points (Figure 5A).…”

MicroRNA-Mediated Regulation of Initial Host Responses in a Symbiotic Organ

“…For instance, in the last decade, investigation of a variety of plants and animals has highlighted the importance of miRNAs in posttranscriptional regulation; notably, in some cases, miRNAs have been shown to be essential for the symbiotic state (53)(54)(55)(56)(57)(58)(59). However, to date, only in the well-studied legume-rhizobia root nodule symbioses has the role of gene regulation by miRNAs been analyzed in detail throughout the ;20-day trajectory from initiation to a functioning symbiotic organ (60,61).…”