AUTHOR=Zhou Guang-Can , Li Wen , Zhang Yan-Mei , Liu Yang , Zhang Ming , Meng Guo-Qing , Li Min , Wang Yi-Lei 

TITLE=Distinct Evolutionary Patterns of NBS-Encoding Genes in Three Soapberry Family (Sapindaceae) Species

JOURNAL=Frontiers in Genetics

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/genetics/articles/10.3389/fgene.2020.00737

DOI=10.3389/fgene.2020.00737

ISSN=1664-8021

ABSTRACT=<p>Nucleotide-binding site (NBS)-type disease resistance genes (<italic>R</italic> 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 <italic>Xanthoceras sorbifolium</italic> (180), <italic>Dinnocarpus longan</italic> (568), and <italic>Acer yangbiense</italic> (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 <italic>X. sorbifolium</italic>, <italic>D. longan</italic>, and <italic>A. yangbiense</italic> 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, <italic>X. sorbifolium</italic> exhibited a “first expansion and then contraction” evolutionary pattern, while <italic>A. yangbiense</italic> and <italic>D. longan</italic> exhibited a “first expansion followed by contraction and further expansion” evolutionary pattern. However, further expansion in <italic>D. longan</italic> was stronger than in <italic>A. yangbiense</italic> after divergence, suggesting that <italic>D. longan</italic> 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.</p>