title: Flavonoid-induced calcium signalling in Rhizobium leguminosarum bv. viciae.
abstract: • Legume-rhizobium symbiosis requires a complex dialogue based on the exchange of diffusible signals between the partners. Compatible rhizobia express key nodulation (nod) genes in response to plant signals - flavonoids - before infection. Host plants sense counterpart rhizobial signalling molecules - Nod factors - through transient changes in intracellular free-calcium. Here we investigate the potential involvement of Ca(2+) in the symbiotic signalling pathway activated by flavonoids in Rhizobium leguminosarum bv. viciae. • By using aequorin-expressing rhizobial strains, we monitored intracellular Ca(2+) dynamics and the Ca(2+) dependence of nod gene transcriptional activation. • Flavonoid inducers triggered, in R. leguminosarum, transient increases in the concentration of intracellular Ca(2+) that were essential for the induction of nod genes. Signalling molecules not specifically related to rhizobia, such as strigolactones, were not perceived by rhizobia through Ca(2+) variations. A Rhizobium strain cured of the symbiotic plasmid responded to inducers with an unchanged Ca(2+) signature, showing that the transcriptional regulator NodD is not directly involved in this stage of flavonoid perception and plays its role downstream of the Ca(2+) signalling event. • These findings demonstrate a key role played by Ca(2+) in sensing and transducing plant-specific flavonoid signals in rhizobia and open up a new perspective in the flavonoid-NodD paradigm of nod gene regulation.
authors.affiliation: Dipartimento di Biologia, Università di Padova, Padova, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Moscatiello
authors.forename: Andrea
authors.initials: A
authors.lastname: Squartini
authors.forename: Paola
authors.initials: P
authors.lastname: Mariani
authors.forename: Lorella
authors.initials: L
authors.lastname: Navazio
mesh_terms: D000331:Aequorin; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000235:genetics / Q000502:physiology*; D005419:Flavonoids / Q000502:physiology*; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D010957:Plasmids; D016961:Rhizobium leguminosarum / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D013559:Symbiosis / Q000502:physiology; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation; D033022:Vicia sativa / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D005419:Flavonoids; D014157:Transcription Factors; D000331:Aequorin; D002118:Calcium