THE PHYTOCHROME GENE FAMILY IN GRASSES (POACEAE) - A PHYLOGENY AND EVIDENCE THAT GRASSES HAVE A SUBSET OF THE LOCI FOUND IN DICOT ANGIOSPERMS

The phytochrome nuclear gene family encodes photoreceptor proteins tha t mediate developmental responses to red and far red light throughout the life of the plant. From studies of the dicot flowering plant Arabi dopsis, the family has been modeled as comprising five loci, PHYA-PHYE . However, it has been shown recently that the Arabidopsis model may n ot completely represent some flowering plant groups because additional PHY loci related to PHYA and PHYB of Arabidopsis apparently have evol ved independently several times in dicots, and monocot flowering plant s may lack orthologs of PHYD and PHYE of Arabidopsis. Nonetheless, the phytochrome nucleotide data were informative in a study of organismal evolution because the loci occur as single copy sequences and appear to be evolving independently. We have continued our investigation of t he phytochrome gene family in flowering plants by sampling extensively in the grass family. The phytochrome nuclear DNA data were cladistica lly analyzed to address the following questions: (1) Are the data cons istent with a pattern of differential distribution of phytochrome gene s among monocots and higher dicots, with homologs of PHYA, B, C, D, an d E present in higher dicots, but of just PHYA, B, and C in monocots, and (2) what phylogenetic pattern within Poaceae do they reveal? Resul ts of these analyses, and of Southern blot experiments, are consistent with the observation that the phytochrome gene family in grasses comp rises the same subset of loci detected in other monocots. Furthermore, for studies of organismal phylogeny in the grass family, the data are shown to provide significant support for relationships that are just weakly resolved by other data sets.