ABSTRACT
The nucleotide-binding site and leucine-rich repeat (NBS-LRR) genes, one of the largest gene families in plants, are evolving rapidly and playing a critical role in plant resistance to pathogens. In this study, a genome-wide search in 12 Rosaceae genomes screened out 2188 NBS-LRR genes, with the gene number varied distinctively across different species. The reconciled phylogeny revealed 102 ancestral genes (7 RNLs, 26 TNLs, and 69 CNLs), which underwent independent gene duplication and loss events during the divergence of the Rosaceae. The NBS-LRR genes exhibited dynamic and distinct evolutionary patterns in the 12 Rosaceae species due to independent gene duplication/loss events, which resulted the discrepancy of NBS-LRR gene number among Rosaceae species. Specifically, Rubus occidentalis, Potentilla micrantha, Fragaria iinumae and Gillenia trifoliata, displayed a "first expansion and then contraction" evolutionary pattern; Rosa chinensis exhibited a "continuous expansion" pattern; F. vesca had a "expansion followed by contraction, then a further expansion" pattern, three Prunus species and three Maleae species shared a "early sharp expanding to abrupt shrinking" pattern. Overall, this study elucidated the dynamic and complex evolutionary patterns of NBS-LRR genes in the 12 Rosaceae species, and could assist further investigation of mechanisms driving these evolutionary patterns.
ABSTRACT
Nucleotide-binding site (NBS)-type disease resistance genes (R genes) play key roles in plant immune responses and have co-evolved with pathogens over the course of plant lifecycles. Comparative genomic studies tracing the dynamic evolution of NBS-encoding genes have been conducted using many important plant lineages. However, studies on Sapindaceae species have not been performed. In this study, a discrepant number of NBS-encoding genes were identified in the genomes of Xanthoceras sorbifolium (180), Dinnocarpus longan (568), and Acer yangbiense (252). These genes were unevenly distributed and usually clustered as tandem arrays on chromosomes, with few existed as singletons. The phylogenetic analysis revealed that NBS-encoding genes formed three monophyletic clades, RPW8-NBS-LRR (RNL), TIR-NBS-LRR (TNL), and CC-NBS-LRR (CNL), which were distinguished by amino acid motifs. The NBS-encoding genes of the X. sorbifolium, D. longan, and A. yangbiense genomes were derived from 181 ancestral genes (three RNL, 23 TNL, and 155 CNL), which exhibited dynamic and distinct evolutionary patterns due to independent gene duplication/loss events. Specifically, X. sorbifolium exhibited a "first expansion and then contraction" evolutionary pattern, while A. yangbiense and D. longan exhibited a "first expansion followed by contraction and further expansion" evolutionary pattern. However, further expansion in D. longan was stronger than in A. yangbiense after divergence, suggesting that D. longan gained more genes in response to various pathogens. Additionally, the ancient and recent expansion of CNL genes generated the dominance of this subclass in terms of gene numbers, while the low copy number status of RNL genes was attributed to their conserved functions.
ABSTRACT
RNA interference (RNAi) refers to a mechanism in which cells control gene expression, protect the genome against mobile repetitive DNA sequences, retro elements and transposons, and defend themselves against viruses. Two core components, dicer and argonaute, are central in the RNAi machinery. In this study the evolution of argonaute and dicer genes were analyzed with 43 fungal genomes, with the focus on Basidiomycota. Argonaute and dicer genes are widely represented in Basidiomycota as well as in other fungal groups, but the number of copies of them vary. However, in certain lineages, argonaute or dicer is missing. Our results suggest an ancient duplication of dicer and argonaute genes concurrently with early diversification of the Basidiomycota followed by additional species-specific duplications and losses of more recent origin. Several distinct RNAi pathways exist in fungi, based on structural similarity and phylogenetic relationship, our results indicate that quelling possibly exists in most Basidiomycota, while we could not find any evidence for the MSUD (meiotic-silencing) pathway in Basidiomycota. RNAi has been developed to be an important tool for reverse genetics studies. Because both argonaute and dicer are present in almost all Basidiomycota our results indicate that it should be possible to develop RNAi as a tool for functional studies of genes in most Basidiomycota species.