Original Paper

Molecular Genetics and Genomics

, Volume 283, Issue 5, pp 427-438

Unique evolutionary pattern of numbers of gramineous NBS–LRR genes

  • Jing LiAffiliated 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
  • , Wen ZhangAffiliated withState Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University
  • , Yuanli ZhangAffiliated withState Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University
  • , Ping TangAffiliated withState Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University
  • , Jian-Qun ChenAffiliated 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 Email author 
  • , Sihai YangAffiliated withState Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University Email author 

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Abstract

Nucleotide binding site (NBS)–leucine-rich repeat (LRR) genes belong to the largest class of disease-resistance gene super groups in plants, and their intra- or interspecies nucleotide variations have been studied extensively to understand their evolution and function. However, little is known about the evolutionary patterns of their copy numbers in related species. Here, 129, 245, 239 and 508 NBSs were identified in maize, sorghum, brachypodium and rice, respectively, suggesting considerable variations of these genes. Based on phylogenetic relationships from a total of 496 ancestral branches of grass NBS families, three gene number variation patterns were categorized: conserved, sharing two or more species, and species-specific. Notably, the species-specific NBS branches are dominant (71.6%), while there is only a small percentage (3.83%) of conserved families. In contrast, the conserved families are dominant in 51 randomly selected house-keeping genes (96.1%). The opposite patterns between NBS and the other gene groups suggest that natural selection is responsible for the drastic number variation of NBS genes. The rapid expansion and/or contraction may be a fundamentally important strategy for a species to adapt to the quickly changing species-specific pathogen spectrum. In addition, the small proportion of conserved NBSs suggests that the loss of NBSs may be a general tendency in grass species.

Keywords

NBS–LRR genes Copy number variation Adaptive evolution Gramineous species