The LAMB1 gene from the clubmoss, Lycopodium annotinum, is a divergent MADS-box gene, expressed specifically in sporogenic structures

Transcription factors encoded by the large MADS-box gene family have import ant developmental functions in angiosperms, the flowering plants. Mutations in certain MADS-box genes are known to cause homeotic alterations in flora l organ identity, and the establishment of floral organ identity is the mos t well-studied developmental process in which MADS-box genes are known to f unction. Our interest is in the potential connection between the duplicatio n history of this gene family and the evolutionary origin of the structures that the different MADS-box genes developmentally regulate in plants. Prev ious studies have demonstrated that the origin of the MADS-box genes that c ontrol floral organ identity predate the evolutionary origin of the flower itself, since gymnosperms have genes that are orthologous to angiosperm flo ral homeotic MADS-box genes, whereas ferns appear to lack such genes. Here we report on the isolation of a MADS-box gene from Lycopodium annotinum, wh ich belongs to the clubmosses, the phylogenetic sister group to other Vascu lar plants. The gene, LAMB1, in the sporophyte is expressed exclusively in the reproductive structure, the strobilus, during sporogenesis. LAMB1 is si milar to other plant MADS-box genes in that it contains a MADS-box as well as a second conserved element, a K-box. However, it differs in length and i n exon/intron structure in the region between the MADS- and K-box, and also in the length and structure of the C-terminal region. A phylogenetic analy sis indicates that LAMB1 is not closely related to other plant-type MADS-bo x genes, and may represent one of the basal branches in the phylogenetic tr ee of plant MADS-box genes. (C) 2000 Elsevier Science B.V. All rights reser ved.