Nitrate-Induced CLE Peptide Systemically Inhibits Nodulation in Medicago truncatula.

Maria Lebedeva,Lyudmila Lutova,Mahboobeh Azarakhsh,Yaroslavna Yashenkova

doi:10.3390/plants9111456

Abstract

Legume plants form nitrogen-fixing nodules in symbiosis with soil bacteria rhizobia. The number of symbiotic nodules is controlled at the whole-plant level with autoregulation of nodulation (AON), which includes a shoot-acting CLV1-like receptor kinase and mobile CLE (CLAVATA3/ENDOSPERM SURROUNDING REGION-related) peptides that are produced in the root in response to rhizobia inoculation. In addition to rhizobia-induced CLE peptides, nitrate-induced CLE genes have been identified in Lotus japonicus and Glycine max, which inhibited nodulation when overexpressed. However, nitrate-induced CLE genes that systemically suppress nodulation in AON-dependent manner have not been identified in Medicago truncatula. Here, we found that MtCLE35 expression is activated by both rhizobia inoculation and nitrate treatment in M. truncatula, similarly to L. japonicus CLE genes. Moreover, we found that MtCLE35 systemically suppresses nodulation in AON-dependent manner, suggesting that MtCLE35 may mediate nitrate-induced inhibition of nodulation in M. truncatula.

Highlights

The Rhizobium–legume interaction results in the formation of new organs on plant roots—symbiotic nodules, where the process of nitrogen fixation takes place
MtCLE35 Is Expressed during Nodulation and in Response to Nitrate Treatment
To study the expression dynamics of the MtCLE35 gene during nodule development, the relative transcript levels of MtCLE35 were analyzed at different stages after inoculation using quantitative reverse transcription polymerase chain reaction (from 3 to 21 dpi)

Summary

Introduction

The Rhizobium–legume interaction results in the formation of new organs on plant roots—symbiotic nodules, where the process of nitrogen fixation takes place. Nodule number is regulated by the plant systemically, and this process is known as autoregulation of nodulation (AON) [1]. A key component of AON is a CLAVATA 1 (CLV1)-like receptor kinase encoded by SUPER NUMERIC NODULES (MtSUNN) in Medicago truncatula, HYPER NODULATION ABERRANT ROOT FORMATION1. A grafting experiment demonstrated that the supernodulating phenotype of mutants defective in CLV1-like receptor kinase is determined by the shoot part of the plant [8]. A signaling cascade activated by CLV1-like kinase in the shoot suppresses the subsequent nodulation on the roots systemically through a shoot-derived inhibitor, thereby regulating nodule number [1,9,10,11]

Methods

Results

Conclusion