Nod-Factor Perception in Medicago truncatula

Nod factors of Rhizobium have been described as the key to the legume door (Relic et al., 1994) and consequently, Nod factor receptors can be considered as the locks which allow Rhizobium access. This concept lies at the heart of the mechanisms of partner recognition leading to the establishment of the legume-Rhizobium symbiosis. Since the discovery of Rhizobium Nod factors in 1990 (see Dénarié et al., 1996), much attention has been paid to how these intriguing molecules interact with plants and this has led to the recent identification of legume symbiotic receptor genes. These studies were aided by focussing on model systems in which genetic and genomic approaches could be used. In this short review, we present our current knowledge of Nod factor perception in Medicago truncatula, a model legume that is nodulated by Sinorhizobium meliloti.