Oxalate oxidases (OXOs) in cereals have been implicated to play a role in defense response to pathogen infection. While many studies have focused on the rapid evolution of major resistance genes involved in pathogen recognition, relatively little is known about the molecular evolution of defense genes in plant-pathogen coevolution. Here, we analyzed the molecular changes in members of rice OXO genes mapped to chromosome 3 that are associated with resistance to blast. There are four tandemly duplicated oxalate oxidases (OsOxo) in chromosome 3 as well as 70 related sequences forming the cupin superfamily of proteins in the rice genome. These four genes (OsOxo1, OsOXO2, OsOxo3, and OsOxo4) exhibit gt&;90% similarity at the nucleotide and amino acid levels. OsOxo4 have been shown to be expressed in rice-Magnaporthe oryzae interaction. In this study, we analyzed the OXO gene family in rice from 62 rice cultivars belonging to six isozyme groups - indica, japonica, aus/boro, aromatic, deepwater subtype III, and deepwater subtype IV. Analyses of the OsOxo from 62 rice cultivars showed that synonymous substitution rates often exceeded nonsynonymous rates, suggesting that purifying selection is the major factor that maintains OXO protein homogeneity. The average frequency of SNPs (single nucleotide polymorphisms) was 1 per 24, 19, 18, and 31 bp across the coding region for OsOxo1, OsOXo2, OsOxo3, and OsOxo4, respectively. Haplotype and nucleotide diversities were moderate with an average of Hd = 0.76 ± 0.05 and π = 0.03 ± 0.005, respectively. Each locus was made up of one to two major haplotypes that clearly distinguish indica and japonica groups from each other.
Goodwin, P.H.; Reveche, M.Y.; Leach, J.E.; Leung, H.; Vera Cruz, C.M.; Carrillo, M.G.C. Molecular evolution of rice oxalate oxidases –candidate genes for quantitative resistance to rice blast. Presented at the 4th International Rice Blast Conference, 10-13 October 2007, Hunan, China. (2007) 1 pp.