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

• Published in: The Plant cell Vol. 31; no. 1; pp. 68 - 83
• Main Authors: Liu, Jieyu, Rutten, Luuk, Limpens, Erik, van der Molen, Tjitse, van Velzen, Robin, Chen, Rujin, Chen, Yuhui, Geurts, Rene, Kohlen, Wouter, Kulikova, Olga, Bisseling, Ton
• Format: Journal Article
• Language: English
• Published: United States American Society of Plant Biologists 01-01-2019
• Subjects: 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
• ISSN: 1040-4651; 1532-298X
• DOI: 10.1105/tpc.18.00478

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.
(
) 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
start codon in
Furthermore, we identify a remote upstream
-regulatory region required for the expression of
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
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
promoter, strongly suggests that
expression is initially triggered by cytokinin signaling in the pericycle to initiate nodule primordium formation.