Structure and expression of duplicate AGAMOUS orthologues in poplar

To investigate the homeotic systems underlying floral development in a dioe cious tree, and to provide tools for the manipulation of floral development , we have isolated two Populus trichocarpa genes, PTAG1 and PTAG2, homologo us to the Arabidopsis floral homeotic gene AGAMOUS (AG). PTAG1 and PTAG2 ar e located on separate linkage groups, but their non-coding regions are high ly similar, consistent with a phylogenetically recent duplication. Intron/e xon structure is conserved in relation to AG and the Antirrhinum AG ortholo gue, PLENA (PLE), and low-stringency Southern analysis demonstrated the abs ence of additional genes in the poplar genome with significant PTAG1/2 homo logy. PTAG1 and PTAG2 exhibit an AG-like floral expression pattern, and phy logenetic analysis of the AG subfamily strongly supports evolutionary ortho logy to C-class organ identity genes. The high degree of similarity shared by PTAG1 and PTAG2 in both sequence (89% amino acid identity) and expressio n indicates that they are unlikely to be functionally associated with speci fication of tree gender. Unexpectedly, PTAG transcripts were consistently d etected in vegetative tissues.