Flavonoid‐induced calcium signalling in Rhizobium leguminosarum bv. viciae

Abstract

Summary• 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 factorsthrough 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.

Strigolactones fine-tune the root system

“…Perception of the proper flavonoid compounds activates the rhizobial nod genes, resulting in the production and secretion of Nod factors (Oldroyd et al 2011). However, addition of GR24 to rhizobial cell cultures could not induce nod gene expression, indicating that strigolactones do not contribute to the initiation of Nod factor production by the rhizobia (Moscatiello et al 2010;Soto et al 2010). Hence, in the rhizosphere, strigolactones seem to solely act as a recognition signal for arbuscular myccorhizal fungi and parasitic plants and not for rhizobia.…”

Symbiosis with an endobacterium increases the fitness of a mycorrhizal fungus, raising its bioenergetic potential

“…To examine intracellular (Oldroyd, 2013). Rhizobia and AMF also perceive plant signals, eliciting a transient calcium elevation (Moscatiello et al, 2010;Moscatiello et al, 2014). The relevance of calcium signalling as a mediator of extra-and intracellular stimuli is well described for many filamentous fungi (Bencina et al, 2005), and for Rhizophagus (Liu et al, 2013).…”

Differential accumulation of flavonoids by tomato (<i>Solanum lycopersicum</i>) fruits tissues during maturation and ripening

“…In some plant species flavonoids are required for the growth of the pollen tube (Yistra et al, 1992;Eldik et al, 1997;Guyon et al, 2000;Antognoni et al, 2004) and seed development (Jiang et al, 2013;Lee et al, 2013;Vogt et al, 1994). They also act in plants as allelochemicals (Taylor and Grotewold, 2005;Li et al, 2010;Filho et al, 2013;Liu et al, 2013;Weston and Mathesius, 2013), signalling molecules in symbiotic associations (Zhang et al, 2007;Maj et al, 2010;Mandal et al, 2010;Moscatiello et al, 2010;Zhang and Franken, 2014) and growth inhibitors (Phillips, 1962;Thimann, 1963;Brown et al, 2001;Yoshioda et al, 2004;Besseau et al, 2007;Brunetti et al, 2013). In human and animal nutrition flavonoids are considered as potentially health-promoting substances due to their anti-oxidative, anti-cancer, anti-diabetes and cardiovascular protective effects (Knekt et al, 1996;Knekt et al, 1997;Böhm et al, 1998;Knekt et al, 2002;Ross and Kasum, 2002;Lin et al, 2007;Naruszewicz et al, 2007;Peñarrieta et al, 2008;Sato et al, 2008).…”