In Medicago truncatula high rates of somatic embryo formation can be induced in the Jemalong genotype 2HA by application of the hormones auxin and cytokinin. Biosynthesis of the stress-related hormone ethylene is also necessary for somatic embryogenesis (SE) and is most likely a response to wounding and the presence of auxin in the medium. We have demonstrated that expression of a gene designated Mt SOMATIC EMBRYO RELATED FACTOR 1 (MtSERF1) induced by ethylene, in the presence of auxin plus cytokinin, is essential for SE. The promoter region of this transcription factor, a member of the ERF sub-family of the AP2/ERF super family, contains putative binding sites relating to auxin and cytokinin in addition to ethylene. An additional finding was the presence of WUSCHEL (WUS) binding sites in the MtSERF1 promoter region, which is discussed. Here we also discuss the Medicago data in the context of embryogenesis studies in Arabidopsis and suggest that MtSERF1 has a key developmental role, possibly in conjunction with WUS, in regulating downstream genes required for the initiation of SE.