title: Rhizobial synthesized cytokinins contribute to but are not essential for the symbiotic interaction between photosynthetic Bradyrhizobia and Aeschynomene legumes.
abstract: Cytokinins (CK) play an important role in the formation of nitrogen-fixing root nodules. It has been known for years that rhizobia secrete CK in the extracellular medium but whether they play a role in nodule formation is not known. We have examined this question using the photosynthetic Bradyrhizobium sp. strain ORS285 which is able to nodulate Aeschynomene afraspera and A. indica using a Nod-dependent or Nod-independent symbiotic process, respectively. CK profiling showed that the most abundant CK secreted by Bradyrhizobium sp. strain ORS285 are the 2MeS (2-methylthiol) derivatives of trans-zeatin and isopentenyladenine. In their pure form, these CK can activate legume CK receptors in vitro, and their exogenous addition induced nodule-like structures on host plants. Deletion of the miaA gene showed that transfer RNA degradation is the source of CK production in Bradyrhizobium sp. strain ORS285. In nodulation studies performed with A. indica and A. afraspera, the miaA mutant had a 1-day delay in nodulation and nitrogen fixation. Moreover, A. indica plants formed considerably smaller but more abundant nodules when inoculated with the miaA mutant. These data show that CK produced by Bradyrhizobium sp. strain ORS285 are not the key signal triggering nodule formation during the Nod-independent symbiosis but they contribute positively to nodule development in Aeschynomene plants.
authors.forename: Kateřina
authors.initials: K
authors.lastname: Podlešáková
authors.forename: Joel
authors.initials: J
authors.lastname: Fardoux
authors.forename: Delphine
authors.initials: D
authors.lastname: Patrel
authors.forename: Katia
authors.initials: K
authors.lastname: Bonaldi
authors.forename: Ondřej
authors.initials: O
authors.lastname: Novák
authors.forename: Miroslav
authors.initials: M
authors.lastname: Strnad
authors.forename: Eric
authors.initials: E
authors.lastname: Giraud
authors.forename: Lukáš
authors.initials: L
authors.lastname: Spíchal
authors.forename: Nico
authors.initials: N
authors.lastname: Nouwen
mesh_terms: D000114:Acetylene / Q000378:metabolism; D020369:Bradyrhizobium / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D003583:Cytokinins / Q000378:metabolism* / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005030:Ethylenes / Q000378:metabolism; D007887:Fabaceae / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism / Q000382:microbiology*; D017930:Genes, Reporter; D009586:Nitrogen Fixation; D009591:Nitrogenase; D010802:Phylogeny; D010937:Plant Growth Regulators / Q000378:metabolism* / Q000494:pharmacology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D055170:Plant Root Nodulation; D018517:Plant Roots / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism / Q000382:microbiology; D018749:RNA, Plant / Q000235:genetics / Q000378:metabolism; D012343:RNA, Transfer / Q000235:genetics / Q000378:metabolism; D053204:Root Nodules, Plant / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism / Q000382:microbiology; D017384:Sequence Deletion; D015398:Signal Transduction; D013559:Symbiosis
chemical_list: D003583:Cytokinins; D005030:Ethylenes; D010937:Plant Growth Regulators; D010940:Plant Proteins; D018749:RNA, Plant; D012343:RNA, Transfer; C036216:ethylene; D009591:Nitrogenase; D000114:Acetylene