nsp mutants are Nod-minus, Hac-minus (no marked root hair curling with a refractile spot) but limited root hair deformations are induced in the presence of Rhizobium. When Nod factors are added, nsp mutants respond by root hair branching and calcium spiking comparable to wild type plants, but show substantially reduced epidermal nodulin gene expression. nsp mutants are also defective for Nod factor-induction of cortical cell divisions and MtENOD40 expression. Since nsp mutants are pleiotropicaly affected in Nod factor responses, we hypothesize that NSP controls a step of a Nod factor-activated transduction pathway. dmi mutants are also pleiotropically affected in Nod factor responses, but unlike dmi mutants, nsp mutants can establish a normal, effective endomycorrhizal symbiotic interaction. Therefore, NSP would control a step of Nod factor transduction specifically involved in the signalling leading to nodulation.