title: Ortholog alleles at Xa3/Xa26 locus confer conserved race-specific resistance against Xanthomonas oryzae in rice.
abstract: The rice disease resistance (R) gene Xa3/Xa26 (having also been named Xa3 and Xa26) against Xanthomonas oryzae pv. oryzae (Xoo), which causes bacterial blight disease, belongs to a multiple gene family clustered in chromosome 11 and is from an AA genome rice cultivar (Oryza sativa L.). This family encodes leucine-rich repeat (LRR) receptor kinase-type proteins. Here, we show that the orthologs (alleles) of Xa3/Xa26, Xa3/Xa26-2, and Xa3/Xa26-3, from wild Oryza species O. officinalis (CC genome) and O. minuta (BBCC genome), respectively, were also R genes against Xoo. Xa3/Xa26-2 and Xa3/Xa26-3 conferred resistance to 16 of the 18 Xoo strains examined. Comparative sequence analysis of the Xa3/Xa26 families in the two wild Oryza species showed that Xa3/Xa26-3 appeared to have originated from the CC genome of O. minuta. The predicted proteins encoded by Xa3/Xa26, Xa3/Xa26-2, and Xa3/Xa26-3 share 91-99% sequence identity and 94-99% sequence similarity. Transgenic plants carrying a single copy of Xa3/Xa26, Xa3/Xa26-2, or Xa3/Xa26-3, in the same genetic background, showed a similar resistance spectrum to a set of Xoo strains, although plants carrying Xa3/Xa26-2 or Xa3/Xa26-3 showed lower resistance levels than the plants carrying Xa3/Xa26. These results suggest that the Xa3/Xa26 locus predates the speciation of A and C genome, which is approximately 7.5 million years ago. Thus, the resistance specificity of this locus has been conserved for a long time.
authors.affiliation: National Key Laboratory of Crop Genetic Improvement, National Center of Plant Gene Research (Wuhan), Huazhong Agricultural University, Wuhan 430070, China.
authors.forename: Hong-Jing
authors.initials: HJ
authors.lastname: Li
authors.forename: Xiang-Hua
authors.initials: XH
authors.lastname: Li
authors.forename: Jing-Hua
authors.initials: JH
authors.lastname: Xiao
authors.forename: Rod A
authors.initials: RA
authors.lastname: Wing
authors.forename: Shi-Ping
authors.initials: SP
authors.lastname: Wang
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D060467:Disease Resistance; D018506:Gene Expression Regulation, Plant; D008969:Molecular Sequence Data; D012275:Oryza / Q000737:chemistry / Q000235:genetics / Q000276:immunology* / Q000382:microbiology; D010935:Plant Diseases / Q000276:immunology / Q000382:microbiology*; D011494:Protein Kinases / Q000737:chemistry / Q000235:genetics* / Q000276:immunology*; D020794:Receptor Protein-Tyrosine Kinases; D016415:Sequence Alignment; D013045:Species Specificity; D014974:Xanthomonas / Q000276:immunology / Q000502:physiology*
chemical_list: D011494:Protein Kinases; D020794:Receptor Protein-Tyrosine Kinases; C486360:Xa26 protein, Oryza sativa