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Plant Cell. 2019 Jan 4. pii: tpc.00478.2018. doi: 10.1105/tpc.18.00478. [Epub ahead of print]

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

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wageningen university CITY: wageningen Netherlands [NL].
Wageningen University & Research CITY: Wageningen Netherlands [NL].
Wageningen University and Research CITY: Wageningen STATE: Gelderland POSTAL_CODE: 6708 PB Netherlands [NL].
Wageningen University and Research CITY: Wageningen STATE: Gelderland Netherlands [NL].
Lanzhou University CITY: Lanzhou STATE: Gansu China [CN].
Noble Foundation CITY: Ardmore United States Of America [US].
Wageningen University CITY: Wageningen POSTAL_CODE: 6708PB Netherlands [NL].
Wageningen University Droevendaalsesteeg 1 CITY: Wageningen POSTAL_CODE: 6708 PB Netherlands [NL].
Wageningen University CITY: Wageningen STATE: Netherlands Netherlands [NL].
Wageningen University & Research CITY: Wageningen POSTAL_CODE: 6708 PB Netherlands [NL]


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 CRE1, 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 signalling in the pericycle to initiate nodule primordium formation.


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