A DEF/GLO-like MADS-Box gene from a gymnosperm: Pinus radiata contains an ortholog angiosperm B class floral homeotic genes

The specification of floral organ identity during development depends on th e function of a limited number of homeotic genes grouped into three classes : A, B, and C. Pairs of paralogous B class genes, such as DEF and GLO in An tirrhinum, and AP3 and Pl in Arabidopsis, are required for establishing pet al and stamen identity. To gain a better understanding of the evolutionary origin of pet als and stamens, we have looked for orthologs of B class gene s in conifers. Here we report cDNA cloning of PrDGL (Pinus radiata DEF/GLO- like gene) from radiata pine. We provide phylogenetic evidence that PrDGL i s closely related to both DEF and GLO-like genes of angiosperms, and is thu s among the first putative orthologs of floral homeotic B function genes ev er reported from a gymnosperm. Expression of PrDGL is restricted to the pol len strobili (male cones) and was not detected in female cones. PrDGL expre ssion was first detected in emergent male cone primordia and persisted thro ugh the early stages of pollen cone bud differentiation. Based on the resul ts of our phylogeny reconstructions and expression studies, we suggest that PrDGL could play a role in distinguishing between male (where expression i s on) and female reproductive structures (where expression is oft) in radia ta pine. We speculate that this could be the general function of DEF/GLO li ke genes in gymnosperms that may have been recruited for the distinction be tween stamens and carpels, the male and female reproductive organs of flowe ring plants, during the evolution of angiosperms out of gymnosperm-like anc estors. (C) 1999 Wiley-Liss, Inc.