Journal Article

A Remote cis-Regulatory Region Is Required for NIN Expression in the Pericycle to Initiate Nodule Primordium Formation in Medicago truncatula

Chen, Yuhui, Chen, Rujin, Geurts, Rene, Limpens, Erik, Rutten, Luuk, Kohlen, Wouter, van Velzen, Robin, Bisseling, Ton, Liu, Jieyu, van der Molen, Tjitse, Kulikova, Olga

2019

Overview

The legume-rhizobium symbiosis results in nitrogen-fixing root nodules, and their formation involves both intracellular infection initiated in the epidermis and nodule organogenesis initiated in inner root cell layers. NODULE INCEPTION (NIN) is a nodule-specific transcription factor essential for both processes. These NIN-regulated processes occur at different times and locations in the root, demonstrating a complex pattern of spatiotemporal regulation. We show that regulatory sequences sufficient for the epidermal infection process are located within a 5 kb region directly upstream of the NIN start codon in Medicago truncatula. Furthermore, we identify a remote upstream cis-regulatory region required for the expression of NIN in the pericycle, and we show that this region is essential for nodule organogenesis. This region contains putative cytokinin response elements and is conserved in eight more legume species. Both the cytokinin receptor 1, which is essential for nodule primordium formation, and the B-type response regulator RR1 are expressed in the pericycle in the susceptible zone of the uninoculated root. This, together with the identification of the cytokinin-responsive elements in the NIN promoter, strongly suggests that NIN expression is initially triggered by cytokinin signaling in the pericycle to initiate nodule primordium formation.

• Publisher: American Society of Plant Biologists (ASPB),American Society of Plant Biologists
• Subject: Biosystematics / Biosystematiek / EPS / Gene Expression Regulation, Plant - genetics / Gene Expression Regulation, Plant - physiology / Laboratorium voor Moleculaire biologie / Laboratory of Molecular Biology / Medicago truncatula - genetics / Medicago truncatula - metabolism / Plant Proteins - genetics / Plant Proteins - metabolism / Plant Root Nodulation - genetics / Plant Root Nodulation - physiology / Plant Roots - genetics / Plant Roots - metabolism / Rhizobium - genetics / Rhizobium - metabolism / Root Nodules, Plant - genetics / Root Nodules, Plant - metabolism