Medicago truncatula

Germain, Alexandre de Saint, Retailleau, Pascal, Norsikian, Stéphanie, Servajean, Vincent, Pelissier, Franck, Steinmetz, Vincent, Pillot, Jean-Paul, Rochange, Soizic, Pouvreau, Jean-Bernard & Boyer, François-Didier, 2019, Contalactone, a contaminant formed during chemical synthesis of the strigolactone reference GR 24 is also a strigolactone mimic, Phytochemistry 168, pp. 1-10 : 4

2.6. (±)-Contalactone induces the colonization of AM fungi in Medicago truncatula

SLs are known to increase hyphal branching of AM fungi ( Akiyama et al., 2005; Besserer et al., 2006) and this biological response can be measured in vitro to characterize the activity of SLs, SL analogs and mimics ( Akiyama et al., 2010; Mori et al., 2016). However, a causal link between this branching response and symbiosis has not been established. Here, we used a different assay in which SL-deficient mutants of M. truncatula are inoculated with the AM fungus Rhizophagus irregularis . The roots of these mutants are hardly colonized, likely due to deficient stimulation of the AM fungus. Treatment with (±)- GR 24 can increase the number of root infection units ( Fig. 7 ), and thus this test can be used as a bioassay to assess the effect of SL mimics on AM symbiotic ability. (±)-Contalactone applied at 100 nM was able to enhance significantly the level of root colonization by R. irregularis , although the activity was slightly lower than that of (±)- GR 24 ( Fig. 7 ). Thus, in addition to the effects on plants reported above, (±)-contalactone also shows significant bioactivity on symbiotic fungi.

Figures

Fig. 7. Effect of (±)-contalactone on symbiotic ability of the AM fungus Rhizophagus irregularis. This fungus was inoculated on Medicago truncatula SL- deficient mutants, in the absence (CTL0) or presence of SL analogs at 10 −7 M. The number of infection points was recorded three weeks post-inoculation. Bars represent the mean ± SE of 9–12 replicates per condition. ***P <0.001, **P <0.01, Mann-Whitney test, compared to control values (CTL0).