Journal
NEW PHYTOLOGIST
Volume 188, Issue 3, Pages 814-823Publisher
WILEY
DOI: 10.1111/j.1469-8137.2010.03411.x
Keywords
aequorin; calcium signalling; flavonoids; legume-rhizobium symbiosis; NodD; Rhizobium leguminosarum bv; viciae
Categories
Funding
- Progetti di Ricerca di Ateneo from the University of Padova [CPDA063434]
- Programmi di Ricerca Scientifica di Rilevante Interesse Nazionale [2008WKPAWW]
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P>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 Ca2+ in the symbiotic signalling pathway activated by flavonoids in Rhizobium leguminosarum bv. viciae. By using aequorin-expressing rhizobial strains, we monitored intracellular Ca2+ dynamics and the Ca2+ dependence of nod gene transcriptional activation. Flavonoid inducers triggered, in R. leguminosarum, transient increases in the concentration of intracellular Ca2+ 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 Ca2+ variations. A Rhizobium strain cured of the symbiotic plasmid responded to inducers with an unchanged Ca2+ signature, showing that the transcriptional regulator NodD is not directly involved in this stage of flavonoid perception and plays its role downstream of the Ca2+ signalling event. These findings demonstrate a key role played by Ca2+ 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.
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