CHARACTERIZATION OF AN AGAMOUS HOMOLOG FROM THE CONIFER BLACK SPRUCE (PICEA-MARIANA) THAT PRODUCES FLORAL HOMEOTIC CONVERSIONS WHEN EXPRESSED IN ARABIDOPSIS

Advances in elucidating the molecular processes controlling flower ini tiation and development have provided unique opportunities to investig ate the developmental genetics of non-flowering plants. In addition to providing insights into the evolutionary aspects of seed plants, iden tification of genes regulating reproductive organ development in gymno sperms could help determine the level of homology with current models of flower induction and floral organ identity. Based upon this, we hav e searched for putative developmental regulators in conifers with amin o acid sequence homology to MADS-box genes. PCR cloning using degenera te primers targeted to the MADS-box domain revealed the presence of ov er 27 MADS-box genes within black spruce (Picea mariana), including se veral with extensive homology to either API or AGAMOUS, both known to regulate flower development in Arabidopsis. This indicates that like a ngiosperms, conifers contain a large and diverse MADS-box gene family that probably includes regulators of reproductive organ development. C onfirmation of this was provided by the characterization of an AGAMOUS -like cDNA clone called SAG1, whose conservation of intron position an d tissue-specific expression within reproductive organs indicate that it is a homologue of AGAMOUS. Functional homology with AGAMOUS was dem onstrated by the ability of SAG1 to produce homeotic conversions of se pals to carpels and petals to stamens when ectopically expressed in tr ansgenic Arabidopsis. This suggests that some of the genetic pathways controlling flower and cone development are homologous, and antedate t he 300-million-year-old divergence of angiosperms and gymnosperms.