IDENTIFICATION OF A HOMEOBOX-CONTAINING GENE WITH ENHANCED EXPRESSIONDURING SOYBEAN (GLYCINE-MAX L) SOMATIC EMBRYO DEVELOPMENT

Homeotic genes are key 'switches' that control developmental processes . Homeotic genes containing the consensus 'homeobox' domain have been identified from a number of organisms including Drosophila melanogaste r, Caenorhabditis elegans, Homo sapiens, and Zea mays. Although homeot ic genes have been demonstrated to be important in embryo development of some insects, amphibians, and mammals, there are no reports of thei r involvement in plant embryogenesis. Here, we report the isolation an d characterization of a cDNA clone for a homeobox-containing gene expr essed in somatic embryos of soybean. The cDNA (Sbh1 for soybean homeob ox containing gene) was isolated using maize Knotted-1 (Kn1) cDNA as a heterologous probe. The Sbh1 cDNA clone is 1515 bp long which is the approximate size of its transcript. Within the homeodomain, the amino acid sequence of a helix-turn-helix structure, and invariant and conse rved residues were identified. The deduced SBH1 protein shares a high amino acid identity with KN1 protein (47.0% overall and 87.5% for the homeodomain). Southern hybridization analysis indicated that Sbh1 is a member of a small gene family. The expression of Sbh1 is development- and tissue-specific. The transcript of Sbh1 was present in early-stag e somatic embryos, increased prior to cotyledon formation and decrease d thereafter. Sbh1 was weakly expressed in soybean stems and hypocotyl but was not detected in other plant tissues and nonembryogenic materi als. The enhanced expression during embryogenesis, the homology with m aize Kn1 gene, and the regulatory nature of homeodomain proteins sugge st that the SBH1 protein plays an important role in plant embryo devel opment.