Phylogeny and Genome Evolution of Oryza (Poaceae)

Michigan State University, East Lansing MI

Investigators

Abstract

0089701 Sang Rice, Oryza sativa, is the world's most important food crop. It is one of two cultivated species (with African cultivated rice, O. glaberrima) in a genus with 21 additional wild species, distributed in Asia, Africa, Australia, and Latin America. Both diploid and tetraploid species are known (plants with double the number of chromosomes), the latter suspected to be stabilized hybrids of various combinations of diploid (2n=24) rices. With colleagues in the U.S. and China, Dr. Tao Sang is addressing four major goals related to the evolution and classification of rice species: (1) reconstruct a phylogeny of the 23 species of Oryza and nearby grass relatives from gene sequences from 12 nuclear single- or few-copy genes plus the chloroplast matK gene; (2) determine with nuclear and chloroplast molecular markers the likely species parentage of the tetraploid rices, including the likely maternal parent; (3) add new single-copy or low-copy nuclear genes to the systematist's toolkit for species-level phylogenetic resolution; and (4) integrate genomic methods with modern systematic practices, particularly in the analysis of hybrids and polyploids. Dr. Sang has accumulated preliminary comparative data for 7 nuclear genes already, thought to mark 5 different linkage groups (chromosomes) of rice; the goal of the 12 genes is to represent nearly all 12 chromosomes in combined-genes analyses, to determine congruence and distinguish "gene phylogenies" from "species phylogenies." Collaboration with Dr. Song Ge at the Institute of Botany, Chinese Academy of Sciences has ensured representative sampling of all species of Oryza and of several outgroup taxa, usually from multiple accessions. Special efforts are being made to detect cases of gene silencing or deletion at homoeologous loci in the tetraploids, and to search for patterns in such changes that may prove of general significance in the evolution of polyploid plants.