First indications for the involvement of strigolactones on nodule formation in alfalfa (Medicago sativa)

Strigolactones fine-tune the root system

“…2) (Soto et al 2010), supporting the role of strigolactones in regulating organ development. In agreement, the pea mutant rms1 was shown to carry less nodules per gram weight compared to control plants and this effect was complemented by exogenous GR24 (Foo and Davies 2011).…”

“…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.…”

Strigolactone Involvement in Root Development, Response to Abiotic Stress, and Interactions with the Biotic Soil Environment

“…Application of GR24 to rms1 plants resulted in an increase in the number of nodules on the mutant roots to the level obtained on the wild type (without exogenous application of strigolactones). GR24 application can also enhance nodule number in wild-type pea, alfalfa, and Lotus japonicus (Soto et al, 2010;Foo and Davies, 2011;Liu et al, 2013). It was also shown that strigolactones in the root but not shoot-derived factors can regulate nodule number (Foo et al, 2014).…”

“…It was only later that strigolactones were also identified as stimulants of hyphal branching in AMF (Akiyama et al, 2005;Besserer et al, 2006Besserer et al, , 2008Gomez-Roldan et al, 2008;Yoneyama et al, 2008). In addition, strigolactones were shown to stimulate nodulation (Nod) in the legume-rhizobium interaction process (Soto et al, 2010;Foo and Davies, 2011).…”

“…Genetic studies indicated that strigolactones may act relatively early in nodule formation rather than during nodule organogenesis (Foo et al, 2013a(Foo et al, , 2013b. Moreover, it was shown that strigolactones do not influence nodulation by acting directly on the rhizobium bacteria (Soto et al, 2010) or the calcium signaling that follows flavonoid perception (Moscatiello et al, 2010). It was suggested that strigolactones are not essential for the development of a functional nodule but may be important in determining the optimal nodule number, thereby having a quantitative effect on nodulation in pea (Foo et al, 2014).…”