1. Relative ENOD11 expression Relative ENOD40 expression Relative NIN expression ba c * * * Figure S1: The response of M. truncatula roots to Sinorhizobium meliloti Nod factors. qRT-PCR analysis of the relative expression levels of nodulation marker genes in response to Nod factors in wild-type A17 roots, in absence of nitrogen (Low Nitrogen, LN) or with 10 mM of NH 4 NO 3 (High Nitrogen, HN). (a) ENOD11, (b) NIN, (c) ENOD40 (Minami et al., 1996; Kosuta et al., 2003; Marsch et al., 2007) Error bars represent SEM, the star indicates a significant difference between the two treatments according to the Mann-Whitney test (n = 3 independent pools of 10 plants, p < 0.05). References Kosuta S, Chabaud M, Lougnon G, Gough C, Dénarié J, Barker DG, Bécard G. 2003. A diffusible factor from arbuscular mycorrhizal fungi induces symbiosis-specific MtENOD11 expression in roots of Medicago truncatula. Plant Physiology 131: 952–962. Marsh JF, Rakocevic A, Mitra RM, Brocard L, Sun J, Eschstruth A, Long SR, Schultze M, Ratet P, Oldroyd GE. 2007. Medicago truncatula NIN is essential for rhizobial-independent nodule organogenesis induced by autoactive calcium/calmodulin-dependent protein kinase. Plant Physiology 144: 324–335. Minami E, Kouchi H, Carlson RW, Cohn JR, Kolli VK, Day RB, Ogawa T, Stacey G. 1996. Cooperative action of lipo- chitin nodulation signals on the induction of the early nodulin, ENOD2, in soybean roots. Molecular Plant Microbe Interactions 9: 574–583.

2. Relative NSP1 expression Figure S2: NSP1 expression in plants treated (CO) or not (0) with 10 -8 M of COs for 12h. (n = 3 independent pools of 10 plants). Error bars represent SEM.

3. * * * * ba cd Relative ENOD11 expression Relative Mtr.37912.1.S1_at expression Relative Mtr.35524.1.S1_at expression RelativeMtr.52092.1.S1_s_at expression Figure S3: The response of the nsp1 mutant to a mixture of 10 -8 M sulphated and non-sulphated Myc- LCOs on a high nitrogen medium. qRT-PCR analysis of the relative expression levels of mycorrhization marker genes in response to Myc-LCOs in wild-type A17 and nsp1 mutant roots. (a) ENOD11, (b) Mtr.52092.1.S1_s_at, (c) Mtr.37912.1.S1_at and (d) Mtr.35524.1.S1_at. Error bars represent SEM, the star indicates a significant difference between the two treatments according to the Mann-Whitney test (n = 3 independent pools of 10 plants, p < 0.05).