9634231 Hilu The grass or cereal family Poaceae (Gramineae) is large and economically significant, but it remains taxonomically difficult. Recent results in molecular phylogenetic studies have yielded abundant DNA sequence data bearing on the closest living relatives of the extant grasses and on the major lineages of evolution within the family. With that "first generation" of molecular analyses having established an overall phylogenetic framework for the grass family, scientists are now turning their attention to fine scale analyses of tribe, genus, and species-level relationships. Dr. Khidir Hilu at Virginia Polytechnic Institute and State University is studying the subfamily Chloridoideae, which comprises ca. 150 genera of grasses with a distinctive C4 pathway of photosynthesis. Many of these are southern-hemisphere plants, especially rich in Africa and Australia. The subfamily is characterized by subtle anatomical features of the leaf, presumably related to the biochemical pathways for carbon fixation and transport; but major questions exist about the naturalness of this group of genera, in particular whether different grass lineages may have evolved the same C4 pathway convergently, in response to similar drought-stressed environments. Working with Dr. Nigel Barker from University of Cape Town, South Africa, Dr. Hilu is collecting representative species samples from the Chloridoideae subfamily, for sequence analyses of the chloroplast matK gene, which will be complemented by extensive data already accumulated by Barker for the rbcL gene and by published data for nuclear ribosomal genes. Comparisons among these gene sequences will yield estimates of mutational differences (nucleotide substitutions) between grass taxa, and permit reconstructions of the phylogenetic relationships of the subfamily. In turn, this knowledge will answer questions about the evolution of particular photosynthetic pathways in grasses and their attendant leaf anatomy.
