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Nucleotide-binding leucine-rich-repeat (NLR) genes comprise the largest family of plant disease-resistance genes. Angiosperm NLR genes are phylogenetically divided into the TNL, CNL, and RNL subclasses. NLR copy numbers and subclass composition vary tremendously across angiosperm genomes. However, the evolutionary associations between genomic NLR content and ecological adaptation, or between NLR content and signal transduction components, are poorly characterized because of limited genome availability. In this study, we established an angiosperm NLR atlas (ANNA, https://biobigdata.nju.edu.cn/ANNA/) that includes NLR genes from over 300 angiosperm genomes. Using ANNA, we revealed that NLR copy numbers differ up to 66-fold among closely related species owing to rapid gene loss and gain. Interestingly, NLR contraction was associated with adaptations to aquatic, parasitic, and carnivorous lifestyles. The convergent NLR reduction in aquatic plants resembles the lack of NLR expansion during the long-term evolution of green algae before the colonization of land. A co-evolutionary pattern between NLR subclasses and plant immune pathway components was also identified, suggesting that immune pathway deficiencies may drive TNL loss. Finally, we identified a conserved TNL lineage that may function independently of the EDS1-SAG101-NRG1 module. Collectively, these findings provide new insights into the evolution of NLR genes in the context of ecological adaptation and genome content variation., (Copyright © 2021 The Author. Published by Elsevier Inc. All rights reserved.)

The NBS-LRR genes are functionally responsible for plant resistance to alien pathogens. Here, we show that NBS-LRR genes originated in the common ancestor of the whole green lineage, and have rapidly diverged into three subclasses with different domain combinations (TNL, CNL, and RNL) before the split of green algae., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Key Message: The Rsv1 - h gene in cultivar Suweon 97, which confers resistance to SMVs, was mapped to a 97.5-kb location (29,815,195-29,912,667 bp on chromosome 13) in the Rsv1 locus, thereby providing additional insights into the molecular nature underlying variations in resistance alleles in this particular locus. Soybean mosaic virus (SMV) is a well-known devastating pathogen of soybean (Glycine max (L.) Merrill.) causing significant yield losses and seed quality deterioration. A single dominant allele, Rsv1-h, which confers resistance to multiple SMV strains, was previously reported in the cultivar Suweon 97, but its exact location is unknown. In the present study, Suweon 97 was crossed with a SMV-sensitive cultivar, Williams 82. Inoculating 267 F 2 individuals with two Chinese SMV strains (SC6-N and SC7-N) demonstrated that one single dominant gene confers SMV resistance. Another 1,150 F 2 individuals were then screened for two simple sequence repeat (SSR) markers (BARCSOYSSR_13_1103 and BARCSOYSSR_13_1187) that flank the Rsv1 locus. Seventy-four recombinants were identified and 20 additional polymorphic SSR markers within the Rsv1 region were then employed in genotyping these recombinants. F 2:3 and F 3:4 recombinant lines were also inoculated with SC6-N and SC7-N to determine their phenotypes. The final data revealed that in Suweon 97, the Rsv1-h gene that confers resistance to SC6-N and SC7-N was flanked by BARCSOYSSR_13_1114 and BARCSOYSSR_13_1115, two markers that delimit a 97.5-kb region in the reference Williams 82 genome. In such region, eight genes were present, of which two, Glyma13g184800 and Glyma13g184900, encode the characteristic CC-NBS-LRR type of resistance gene and were considered potential candidates for Rsv1-h.

Nucleotide-binding site-leucine-rich repeat (NBS-LRR) genes make up the largest plant disease resistance gene family (R genes), with hundreds of copies occurring in individual angiosperm genomes. However, the expansion history of NBS-LRR genes during angiosperm evolution is largely unknown. By identifying more than 6,000 NBS-LRR genes in 22 representative angiosperms and reconstructing their phylogenies, we present a potential framework of NBS-LRR gene evolution in the angiosperm. Three anciently diverged NBS-LRR classes (TNLs, CNLs, and RNLs) were distinguished with unique exon-intron structures and DNA motif sequences. A total of seven ancient TNL, 14 CNL, and two RNL lineages were discovered in the ancestral angiosperm, from which all current NBS-LRR gene repertoires were evolved. A pattern of gradual expansion during the first 100 million years of evolution of the angiosperm clade was observed for CNLs. TNL numbers remained stable during this period but were eventually deleted in three divergent angiosperm lineages. We inferred that an intense expansion of both TNL and CNL genes started from the Cretaceous-Paleogene boundary. Because dramatic environmental changes and an explosion in fungal diversity occurred during this period, the observed expansions of R genes probably reflect convergent adaptive responses of various angiosperm families. An ancient whole-genome duplication event that occurred in an angiosperm ancestor resulted in two RNL lineages, which were conservatively evolved and acted as scaffold proteins for defense signal transduction. Overall, the reconstructed framework of angiosperm NBS-LRR gene evolution in this study may serve as a fundamental reference for better understanding angiosperm NBS-LRR genes., (© 2016 American Society of Plant Biologists. All Rights Reserved.)

Plant genomes harbor dozens to hundreds of nucleotide-binding site-leucine-rich repeat (NBS-LRR) genes; however, the long-term evolutionary history of these resistance genes has not been fully understood. This study focuses on five Brassicaceae genomes and the Carica papaya genome to explore changes in NBS-LRR genes that have taken place in this Rosid II lineage during the past 72 million years. Various numbers of NBS-LRR genes were identified from Arabidopsis lyrata (198), A. thaliana (165), Brassica rapa (204), Capsella rubella (127), Thellungiella salsuginea (88), and C. papaya (51). In each genome, the identified NBS-LRR genes were found to be unevenly distributed among chromosomes and most of them were clustered together. Phylogenetic analysis revealed that, before and after Brassicaceae speciation events, both toll/interleukin-1 receptor-NBS-LRR (TNL) genes and non-toll/interleukin-1 receptor-NBS-LRR (nTNL) genes exhibited a pattern of first expansion and then contraction, suggesting that both subclasses of NBS-LRR genes were responding to pathogen pressures synchronically. Further, by examining the gain/loss of TNL and nTNL genes at different evolutionary nodes, this study revealed that both events often occurred more drastically in TNL genes. Finally, the phylogeny of nTNL genes suggested that this NBS-LRR subclass is composed of two separate ancient gene types: RPW8-NBS-LRR and Coiled-coil-NBS-LRR., (© 2015 Institute of Botany, Chinese Academy of Sciences.)

A genome triplication took place in the ancestor of Brassiceae species after the split of the Arabidopsis lineage. The postfragmentation and shuffling of the genome turned the ancestral hexaploid back to diploids and caused the radiation of Brassiceae species. The course of speciation was accompanied by the loss of duplicate genes and also influenced the evolution of retained genes. Of all the genes, those encoding NBS domains are typical R genes that confer resistance to invading pathogens. In this study, using the genome of Arabidopsis thaliana as a reference, we examined the loss/retention of orthologous NBS-encoding loci in the tripled Brassica rapa genome and discovered differential loss/retention frequencies. Further analysis indicated that loci of different retention ratios showed different evolutionary patterns. The loci of classesII and III (maintaining two and three syntenic loci, respectively, multi-loci) show sharper expansions by tandem duplications, have faster evolutionary rates and have more potential to be associated with novel gene functions. On the other hand, the loci that are retained at the minimal rate (keeping only one locus, class I, single locus) showed opposite patterns. Phylogenetic analysis indicated that recombination and translocation events were common among multi-loci in B. rapa, and differential evolutionary patterns between multi- and single-loci are likely the consequence of recombination. Investigations towards other gene families demonstrated different evolutionary characteristics between different gene families. The evolution of genes is more likely determined by the property of each gene family, and the whole genome triplication provided only a specific condition., (Copyright © 2014 Elsevier B.V. All rights reserved.)