Expression of the Medicago Truncatula ENOD12 Gene in Response to R. Meliloti Nod Factors and during Spontaneous Nodulation in Transgenic Alfalfa

Abstract

A complex interplay, involving multiple signal exchange between the legume host and its rhizobial partner, is required for the induction and subsequent development of the N2-fixing symbiotic root nodule. In particular, it has been shown that a sulphated lipo-oligosaccharide (NodRm), purified from the supernatant of Rhizobium meliloti (Lerouge et al., 1990), can act as a specific symbiotic signal to elicit root hair deformations and nodule organogenesis on alfalfa (Medicago sativa) plants (Truchet et al.,1991). It is now established that other Rhizobium species produce different specific symbiotic signal molecules, the so-called Nod factors, with a core structure similar to NodRm (Spaink et al., 1991). Rhizobial nodulation (nod) genes are responsible for the synthesis of Nod factors (Denarie, Roche, 1992). A detailed analysis of the host response to these Nod factors requires the identification of plant genes which can serve as molecular markers for the earliest stages of the recognition, infection and nodule organogenetic triggering processes. Recently, Scheres et al. (1990) have reported that transcripts of a pea gene (PsENOD12), which encodes a proline-rich protein, are present in a variety of cell types involved in the early stages of infection.