Evolution of a family of plant genes with regulatory functions in development; studies on Picea abies and Lycopodium annotinum

Abstract: This work is focused on the molecular genetic basis for morphological change in evolution. Genes belonging to the MADS-box gene family, which includes members, that determine angiosperm floral organ identity, were isolated and characterised from two non-angiosperm plants; Norway spruce (Picea abies) and the club moss (Lycopodium annotinum).The exon/intron organisation of the isolated genes was determined, and its significance as an independent test of the position of a gene within the gene family tree evaluatad. identity genes were identified. One Norway spruce gene, DAL2, is an ortholog toNorway spruce genes that are closely related to the angiosperm floral organ angiosperm C-class MADS-box genes that specify stamen and carpel identity. The expression of DAL2 in male and female cones suggests that orthologous genes in conifers and argiosperms determine the identities of pollen- and seed-bearing structures. Constitutive expression of DAL2 in the angiosperm Arabidopsis resulted in homeotic conversions very similar to those resulting from constiutive expression of the Arabidopsis C-class gene.Angiosperm B-class MADS-box genes determine petal and stamen identity. The isolated Norway spruce B-class orthologs: DAL11, DAL12, and DAL13 are expressed in the developing male cones exclusively, suggesting a conserved function of B-class related genes in the determination of pollen forming organs among seed plants.No orthologs to the floral organ identity genes couId be isolated from the club moss, suggesting that the origin of these gene classes may be coupled to the origin of the pollen and the seed.The club moss MADS-box genes, LAMB2, LAMB4 and LAMB6, conform structurally to plant type MADS-box genes, whereas LAMB1 is divergent in details. The genes LAMB3 and LAMB5 encode shorter proteins.LAMB1 expression is restricted to reproductive structures, whereas LAMB2, LAMB4, LAMB5 and LAMB6 are broadly expressed. The implications from these expression patterns on the ancestral function of plant type MADS-box genes are discussed.