Definition of different activation patterns in Medicago truncatula roots.

+, − and 0 respectively mean induction, repression and no differential expression as compared to control roots. +− means a weaker induction than in the wild type (WT) situations, while ++ indicates the highest level of expression. +/++ indicates that some genes from this class had a + level of expression while others had a ++ level; similarly +/+− indicates that some genes had a + level while others had a +− level. NF stands for response to 10−8 M purified Nod factors (24 h treatment), WT for response to WT S. meliloti. nfp, hcl-1, lin, exoA and efd-1 indicate the tested plant or bacterial mutants.