EVOLUTION OF THE PHYTOCHROME GENE FAMILY AND ITS UTILITY FOR PHYLOGENETIC ANALYSES OF ANGIOSPERMS

The phytochrome gene family encodes photoreceptor proteins that serve many functions throughout the life of a plant. From studies of the ang iosperm Arabidopsis, the family has been modeled as comprising five lo ci, PHYA-PHYE. However, in most nonangiosperms, one locus, or at most two, is present. Moreover, it is shown here that the Arabidopsis model does not completely represent some angiosperm groups. For example, ad ditional PHYloci related to PHYA and PHYB of Arabidopsis have evolved independently several times in dicot angiosperms, and monocot angiospe rms (as well as Piper) may lack orthologs of Arabidopsis PHYD and PHYE Nonetheless, for studies of organismal evolution, the phytochrome gen e family is a potential source of phylogenetic information because the loci occur as single copy sequences, and preliminary data suggest tha t the various loci are evolving independently. In the plant family Fab aceae, phytochrome data are shown to provide phylogenetic resolution t o a taxonomically very difficult tribe of tropical woody genera that i nclude Millettia, Lonchocarpus, and Derris. In addition to nucleotide substitutions, phylogenetically informative insertions and deletions h elped to resolve relationships in this group of legumes. Also, the pre sence of a legume-specific locus related to PHYA should prove to be ph ylogenetically informative once its taxonomic distribution is better u nderstood.