MIR2111-5 locus and shoot-accumulated mature miR2111 systemically enhance nodulation depending on HAR1 in Lotus japonicus

Abstract

Legumes utilize a shoot-mediated signaling system to maintain a mutualistic relationship with nitrogen-fixing bacteria in root nodules. In Lotus japonicus, shoot-to-root transfer of microRNA miR2111 that targets TOO MUCH LOVE, a nodulation suppressor in roots, has been proposed to explain the mechanism underlying nodulation control from shoots. However, the role of shoot-accumulating miR2111s for the systemic regulation of nodulation was not clearly shown. Here, we find L. japonicus has seven miR2111 loci, including those mapped through RNA-seq. MIR2111-5 expression in leaves is the highest among miR2111 loci and repressed after rhizobial infection depending on a shoot-acting HYPERNODULATION ABERRANT ROOT FORMATION1 (HAR1) receptor. MIR2111-5 knockout mutants show significantly decreased nodule numbers and miR2111 levels. Furthermore, grafting experiments using transformants demonstrate scions with altered miR2111 levels influence nodule numbers in rootstocks in a dose-dependent manner. Therefore, miR2111 accumulation in leaves through MIR2111-5 expression is required for HAR1-dependent systemic optimization of nodule number.

Systemic Optimization of Legume Nodulation: A Shoot-Derived Regulator, miR2111

“…To optimize this symbiosis, legumes control nodule numbers using long-distance negative/positive feedback systems in response to rhizobial infection and soil nutrient availability (Caetano-Anollés and Gresshoff, 1991;Ferguson et al, 2019). Accumulating evidence suggests that shoot-derived miR2111 might play a central role in controlling nodule numbers (Tsikou et al, 2018;Gautrat et al, 2020a;Okuma et al, 2020;Zhang et al, 2021). Here, we summarize recent advances in the study of systemic regulation of nodulation in response to external environmental stimuli, particularly focusing on the relevance of shoot-derived miR2111.…”

Dynamics ofmiRNAmediated regulation of legume symbiosis

“…STTM lines of miR2111 led to an increased level of TML and decreased nodulation. Additionally, knockout lines of MIR2111‐5 showed a decrease in nodule number similar to the STTM lines of miR2111 (Okuma et al, 2020). GUS staining revealed that miR2111 expresses in leaves but not in root.…”

“…Overexpression of miR2111c resulted in hyperinfection and an enhanced number of nodules at 21 dpi. Another recent study by Okuma, Soyano, Suzaki, & Kawaguchi, 2020, reported that miR2111‐5 loci in L. japonicus has high expression in leaves and its expression decreases upon rhizobial infection in Hypernodulation aberrant root1 ( HAR1 ) dependent manner (Okuma et al, 2020). STTM lines of miR2111 led to an increased level of TML and decreased nodulation.…”

Microtubules Promote the Non-cell Autonomy of MicroRNAs by Inhibiting their Cytoplasmic Loading into ARGONAUTE1 inArabidopsis

“…Mobile small RNAs may coordinate events in distant plant parts. For example, several miRNAs are induced in shoots and transported to roots to regulate responses to nutrient starvation and nodulation (Buhtz et al, 2010;Lin et al, 2008;Okuma et al, 2020;Pant et al, 2008). Several mobile small RNAs, such as miR165/6, miR394, and the trans-acting siRNA tasiR-ARF, serve as morphogenic signals that pattern cell fates in development (Carlsbecker et al, 2010;Chitwood et al, 2009;Knauer et al, 2013;Miyashima et al, 2011).…”

“…Mobile small RNAs may coordinate events in distant plant parts. For example, several miRNAs are induced in shoots and transported to roots to regulate responses to nutrient starvation and nodulation (Buhtz et al, 2010;Lin et al, 2008;Okuma et al, 2020;Pant et al, 2008). Several mobile small RNAs, such as miR165/6, miR394, and the trans-acting .…”