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Sci. Signal., 9 December 2008
Vol. 1, Issue 49, p. re11
De Novo Organ Formation from Differentiated Cells: Root Nodule Organogenesis
Martin Crespi* and
Institut des Sciences du Végétal (ISV), Centre National de la Recherche Scientifique, 91198 Gif sur Yvette cedex, France.
Gloss: The symbiotic interaction between Rhizobium bacteria and legume plants leads to the formation of a new organ emerging from their roots: the nitrogen-fixing nodule. These organs allow legumes, in contrast to cereals and other nonlegumes, to grow in the absence of nitrogen fertilizers, conferring a major agricultural advantage to these crops. Nodule organogenesis is triggered by specific bacterial signals, the Nod factors, and integrates plant developmental regulatory pathways to reactivate differentiated root cortical cells and initiate the formation of a de novo meristem, a plant stem cell niche. We review recent data showing how the transition from differentiated root cortical cells to meristematic cells leads to development of a new organ. Genetic analyses revealed crucial functions of bacterial Nod factors and the plant hormone cytokinin in nodule organogenesis. Genomic analysis of transcriptional networks activated during early nodulation identified additional regulators of this organogenesis, such as transcription factors and small regulatory RNAs or microRNAs. These pathways shed new light on nodule organogenesis and symbiotic nitrogen fixation in crops and in the acquisition of developmental plasticity by differentiated cells.