title: Rhizobium Lipo-chitooligosaccharide Signaling Triggers Accumulation of Cytokinins in Medicago truncatula Roots.
abstract: Legume rhizobium symbiosis is initiated upon perception of bacterial secreted lipo-chitooligosaccharides (LCOs). Perception of these signals by the plant initiates a signaling cascade that leads to nodule formation. Several studies have implicated a function for cytokinin in this process. However, whether cytokinin accumulation and subsequent signaling are an integral part of rhizobium LCO signaling remains elusive. Here, we show that cytokinin signaling is required for the majority of transcriptional changes induced by rhizobium LCOs. In addition, we demonstrate that several cytokinins accumulate in the root susceptible zone 3 h after rhizobium LCO application, including the biologically most active cytokinins, trans-zeatin and isopentenyl adenine. These responses are dependent on calcium- and calmodulin-dependent protein kinase (CCaMK), a key protein in rhizobial LCO-induced signaling. Analysis of the ethylene-insensitive Mtein2/Mtsickle mutant showed that LCO-induced cytokinin accumulation is negatively regulated by ethylene. Together with transcriptional induction of ethylene biosynthesis genes, it suggests a feedback loop negatively regulating LCO signaling and subsequent cytokinin accumulation. We argue that cytokinin accumulation is a key step in the pathway leading to nodule organogenesis and that this is tightly controlled by feedback loops.
authors: Department of Plant Sciences, Laboratory of Molecular Biology, Wageningen University, Droevendaalsesteeg 1, 6708 PB Wageningen, The Netherlands.
authors: Arjan
authors: A
authors: van Zeijl
authors: Department of Plant Sciences, Laboratory of Molecular Biology, Wageningen University, Droevendaalsesteeg 1, 6708 PB Wageningen, The Netherlands.
authors: Rik H M
authors: RH
authors: Op den Camp
authors: Department of Plant Sciences, Laboratory of Molecular Biology, Wageningen University, Droevendaalsesteeg 1, 6708 PB Wageningen, The Netherlands; Department of Systems Biophysics, FOM institute AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands.
authors: Eva E
authors: EE
authors: Deinum
authors: Department of Plant Sciences, Laboratory of Plant Physiology, Wageningen University, Droevendaalsesteeg 1, 6708 PB Wageningen, The Netherlands.
authors: Tatsiana
authors: T
authors: Charnikhova
authors: Department of Plant Sciences, Laboratory of Molecular Biology, Wageningen University, Droevendaalsesteeg 1, 6708 PB Wageningen, The Netherlands.
authors: Henk
authors: H
authors: Franssen
authors: Department of Microbiology, IWWR, Radboud University Nijmegen, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands.
authors: Huub J M
authors: HJ
authors: Op den Camp
authors: Department of Plant Sciences, Laboratory of Plant Physiology, Wageningen University, Droevendaalsesteeg 1, 6708 PB Wageningen, The Netherlands.
authors: Harro
authors: H
authors: Bouwmeester
authors: Department of Plant Sciences, Laboratory of Molecular Biology, Wageningen University, Droevendaalsesteeg 1, 6708 PB Wageningen, The Netherlands.
authors: Wouter
authors: W
authors: Kohlen
authors: Department of Plant Sciences, Laboratory of Molecular Biology, Wageningen University, Droevendaalsesteeg 1, 6708 PB Wageningen, The Netherlands; College of Science, King Saud University, Post Office Box 2455, Riyadh 11451, Saudi Arabia.
authors: Ton
authors: T
authors: Bisseling
authors: Department of Plant Sciences, Laboratory of Molecular Biology, Wageningen University, Droevendaalsesteeg 1, 6708 PB Wageningen, The Netherlands. Electronic address: rene.geurts@wur.nl.
authors: René
authors: R
authors: Geurts
mesh_terms: D002686:Chitin / Q000031:analogs & derivatives* / Q000494:pharmacology; D048271:Chitosan; D003583:Cytokinins / Q000378:metabolism*; D005030:Ethylenes / Q000494:pharmacology; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D017343:Genes, Plant; D017930:Genes, Reporter; D046913:Medicago truncatula / Q000187:drug effects / Q000235:genetics / Q000378:metabolism* / Q000382:microbiology*; D008954:Models, Biological; D009844:Oligosaccharides; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000187:drug effects / Q000235:genetics / Q000382:microbiology; D012231:Rhizobium / Q000737:chemistry*; D015398:Signal Transduction / Q000187:drug effects* / Q000235:genetics; D013559:Symbiosis / Q000187:drug effects / Q000235:genetics; D013997:Time Factors; D014158:Transcription, Genetic / Q000187:drug effects
chemical_list: D003583:Cytokinins; D005030:Ethylenes; D009844:Oligosaccharides; D010940:Plant Proteins; C493484:oligochitosan; D002686:Chitin; D048271:Chitosan; C036216:ethylene
keywords: CRE1; Medicago truncatula; cytokinin; ethylene; lipo-chitooligosaccharides; rhizobium