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Diversification of defensins and NLRs in Arabidopsis species by different evolutionary mechanisms

Authors
  • Mondragón-Palomino, Mariana1
  • Stam, Remco2
  • John-Arputharaj, Ajay1
  • Dresselhaus, Thomas1
  • 1 University of Regensburg, Cell Biology and Plant Biochemistry, Biochemie-Zentrum Regensburg, Universitätstraße 31, Regensburg, 93053, Germany , Regensburg (Germany)
  • 2 Technical University of Munich, School of Life Sciences Weihenstephan, Chair of Phytopathology, Emil-Ramann-Str. 2, Freising, 85354, Germany , Freising (Germany)
Type
Published Article
Journal
BMC Evolutionary Biology
Publisher
Springer (Biomed Central Ltd.)
Publication Date
Dec 15, 2017
Volume
17
Issue
1
Identifiers
DOI: 10.1186/s12862-017-1099-4
Source
Springer Nature
Keywords
License
Green

Abstract

BackgroundGenes encoding proteins underlying host-pathogen co-evolution and which are selected for new resistance specificities frequently are under positive selection, a process that maintains diversity. Here, we tested the contribution of natural selection, recombination and transcriptional divergence to the evolutionary diversification of the plant defensins superfamily in three Arabidopsis species. The intracellular NOD-like receptor (NLR) family was used for comparison because positive selection has been well documented in its members. Similar to defensins, NLRs are encoded by a large and polymorphic gene family and many of their members are involved in the immune response.ResultsGene trees of Arabidopsis defensins (DEFLs) show a high prevalence of clades containing orthologs. This indicates that their diversity dates back to a common ancestor and species-specific duplications did not significantly contribute to gene family expansion. DEFLs are characterized by a pervasive pattern of neutral evolution with infrequent positive and negative selection as well as recombination. In comparison, most NLR alignment groups are characterized by frequent occurrence of positive selection and recombination in their leucine-rich repeat (LRR) domain as well negative selection in their nucleotide-binding (NB-ARC) domain. While major NLR subgroups are expressed in pistils and leaves both in presence or absence of pathogen infection, the members of DEFL alignment groups are predominantly transcribed in pistils. Furthermore, conserved groups of NLRs and DEFLs are differentially expressed in response to Fusarium graminearum regardless of whether these genes are under positive selection or not.ConclusionsThe present analyses of NLRs expands previous studies in Arabidopsis thaliana and highlights contrasting patterns of purifying and diversifying selection affecting different gene regions. DEFL genes show a different evolutionary trend, with fewer recombination events and significantly fewer instances of natural selection. Their heterogeneous expression pattern suggests that transcriptional divergence probably made the major contribution to functional diversification. In comparison to smaller families encoding pathogenesis-related (PR) proteins under positive selection, DEFLs are involved in a wide variety of processes that altogether might pose structural and functional trade-offs to their family-wide pattern of evolution.

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