title: Adaptive evolution of Xa21 homologs in Gramineae.
abstract: The XA21 protein has broad spectrum resistance against Xanthomonas oryzae pv. oryzae. Although Xa21-mediated immunity is well characterized, little is known about the origin and evolutionary history of this gene in grasses. Therefore, we analyzed all Xa21 gene homologs in eight whole-genome sequenced rice lines, as well as in four gramineous genomes, rice, Brachypodium, sorghum and maize; using Arabidopsis Xa21 homologs as outgroups, 17, 7, 7 and 3 Xa21 homologs were detected in these four grasses, respectively. Synteny and phylogenetic analysis showed that frequent gene translocation, duplication and/or loss, have occurred at Xa21 homologous loci, suggesting that they have undergone or are undergoing rapid generation of copy number variations. Within the rice species, the high level of nucleotide diversity between Xa21-like orthologs showed a strong association with the presence/absence haplotypes, suggesting that the genetic structure of rice lines plays an important role in the variations between these Xa21-like orthologs. Strongly positive selection was detected in the core region of the leucine-rich repeat domains of the Xa21 subclade among the rice lines, indicating that the rapid gene diversification of Xa21 homologs may be a strategy for a given species to adapt to the changing spectrum of species-specific pathogens.
authors.affiliation: State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing, China.
authors.forename: Shengjun
authors.initials: S
authors.lastname: Tan
authors.forename: Dan
authors.initials: D
authors.lastname: Wang
authors.forename: Jing
authors.initials: J
authors.lastname: Ding
authors.forename: Dacheng
authors.initials: D
authors.lastname: Tian
authors.forename: Xiaohui
authors.initials: X
authors.lastname: Zhang
authors.forename: Sihai
authors.initials: S
authors.lastname: Yang
mesh_terms: D000220:Adaptation, Biological / Q000235:genetics*; D017360:Arabidopsis / Q000235:genetics; D019143:Evolution, Molecular; D018745:Genome, Plant; D012275:Oryza / Q000235:genetics; D010802:Phylogeny; D010935:Plant Diseases / Q000235:genetics / Q000276:immunology; D010940:Plant Proteins / Q000235:genetics* / Q000276:immunology; D006109:Poaceae / Q000145:classification / Q000235:genetics*; D011110:Polymorphism, Genetic; D012641:Selection, Genetic
chemical_list: D010940:Plant Proteins