The olive tree is an economically important fruit tree, widely spread in the Mediterranean Basin. The recent availability of two full genomes of this plant offers an opportunity to characterize its disease resistance gene repertoire. The nucleotide-binding site (NBS) gene family accounts for the largest number of known disease resistance genes and is one of the largest gene families in plant genomes. Here, we have identified 270 regular NBS-type genes in the olive genome, roughly representing 0.5% of whole-genome protein-coding genes in this species. A systematic characterization of this gene set was conducted on the bases of conserved protein signatures, gene duplications, phylogenetic relationships, selection pressure, and expression evidence. Several structural features were particularly pronounced in O. europaea, including a very small proportion of TIR-type NBS genes, as well as numerous non-canonical functional domains associated to the NBS. Analyses of duplication and selection pressure strongly suggest that recent duplication, in conjunction with positive selection, played a remarkable role in the evolution of NBS-encoding genes in olive. Based on the phylogenetic tree produced, three pairs of possible orthologs between the olive NBS genes (OeNBS) and those from Arabidopsis thaliana, Oryza sativa Indica, and O. sativa Japonica were identified and could be of interest to characterize the uncharacterized function of the OeNBS genes in olive. Various expression patterns of olive NBS-encoding genes in different tissues were observed using expressed sequence tags (ESTs). Interestingly, we identified a pair of duplicated NLRs integrating an N-terminal RPW8 domain, which are possibly expressed in response to Verticillium dahliae, in addition to a gene encoding C-terminal Armadillo repeat domain, which is possibly induced upon colonization by the endophytic bacterium Pseudomonas fluorescens. This work is the first to characterize NBS family members and report on their architectural, evolutionary, and functional features. Our findings lay an important multifaceted foundation for a deeper understanding of R genes biology in olive tree and provide valuable information for further functional studies.

橄榄树是一种经济上重要的果树，广泛分布于地中海盆地。该植物两个完整基因组的最新可用性提供了表征其抗病基因库的机会。核苷酸结合位点（NBS）基因家族占已知抗病基因的最大数量，并且是植物基因组中最大的基因家族之一。在这里，我们在橄榄基因组中鉴定了270个常规NBS型基因，大约占该物种全基因组蛋白质编码基因的0.5％。在保守的蛋白质特征，基因重复，系统发育关系，选择压力和表达证据的基础上对该基因组进行了系统的表征。欧洲油菜特别突出了几种结构特征包括非常少的TIR型NBS基因，以及与NBS相关的众多非规范功能域。对复制和选择压力的分析强烈表明，最近的复制与阳性选择结合，在橄榄中NBS编码基因的进化中发挥了重要作用。基于所产生的进化树，三对橄榄NBS基因（间可能的同源物的OeNBS）和来自拟南芥，水稻籼，和栽培稻粳进行鉴定，并可能会感兴趣表征的未鉴定的功能OeNBS橄榄中的基因。使用表达的序列标签（EST）观察到橄榄NBS编码基因在不同组织中的各种表达模式。有趣的是，除了编码C末端犰狳重复结构域的基因外，我们鉴定了一对重复的整合了N末端RPW8结构域的NLR，这些基因可能响应黄萎病菌而表达，该基因可能是由内生细菌定植时诱导的荧光假单胞菌。这项工作是第一个表征NBS家族成员并报告其体系结构，演进和功能特征的工作。我们的发现为深入了解R奠定了重要的多方面基础 基因在橄榄树中的生物学，并为进一步的功能研究提供有价值的信息。