Article

Genetica

, Volume 139, Issue 11, pp 1465-1475

Adaptive evolution of Xa21 homologs in Gramineae

  • Shengjun TanAffiliated withState Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University
  • , Dan WangAffiliated withState Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University
  • , Jing DingAffiliated withState Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University
  • , Dacheng TianAffiliated withState Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University
  • , Xiaohui ZhangAffiliated withState Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing UniversityDepartment of Biology, Nanjing University Email author 
  • , Sihai YangAffiliated withState Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing UniversityDepartment of Biology, Nanjing University Email author 

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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.

Keywords

Xa21 Adaptive evolution Syntenic block Positive selection