Figure 1. Model depicting the putative role of MtN5 in rhizobial infection. MtN5 is implicated in the molecular events occurring at the epidermis after perception of nodulation factors (NFs) and phospholipase D (PLD) activation and acts upstream of FLOTILLIN 4 (FLOT4). The function of MtN5 seems independent of DMI1 and NIN. Studies with MtN5-silenced roots indicated MtN5 is required for rhizobial infection, but not for nodule primordia formation. It is not yet established whether this protein could act either on the initiation and progression of infection threads (ITs) or on nodule invasion. The impaired nodule infection observed in MtN5-silenced roots was accompanied by an enhanced responsiveness of root hairs to rhizobia, suggesting MtN5 could participate either directly or indirectly in a mechanism that restricts the competence of root hairs for infection.