Abstract
Tomato (Solanum lycopersicum L.) is a model system for studying the molecular basis of resistance in plants. The investigation of evolutionary dynamics of tomato resistance (R)-loci provides unique opportunities for identifying factors that promote or constrain genome evolution. Nucleotide-binding domain and leucine-rich repeat (NB-LRR) receptors belong to one of the most plastic and diversified families. The vast amount of genomic data available for Solanaceae and wild tomato relatives provides unprecedented insights into the patterns and mechanisms of evolution of NB-LRR genes. Comparative analysis remarked a reshuffling of R-islands on chromosomes and a high degree of adaptive diversification in key R-loci induced by species-specific pathogen pressure. Unveiling NB-LRR natural variation in tomato and in other Solanaceae species offers the opportunity to effectively exploit genetic diversity in genomic-driven breeding programs with the aim of identifying and introducing new resistances in tomato cultivars. Within this motivating context, we reviewed the repertoire of NB-LRR genes available for tomato improvement with a special focus on signatures of adaptive processes. This issue is still relevant and not thoroughly investigated. We believe that the discovery of mechanisms involved in the generation of a gene with new resistance functions will bring great benefits to future breeding strategies.
Highlights
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Species in the Solanum section Lycopersicon originated in the region that extends from Andean Highlands to the coast of Galapagos islands and includes the domesticated tomato and its 12 closest wild relatives (S. arcanum, S. cheesmaniae, S. chilense, S. chmielewskii, S. corneliomulleri, S. galapagense, S. habrochaites, S. huaylasense, S. neorickii, S. pennellii, S. peruvianum and S. pimpinellifolium) [1]
All these findings enhance our understanding of the dynamic evolution of Nucleotidebinding domain and leucine-rich repeat (NB-LRR) and provide insights and a solid foundation for future breeding and molecular engineering for disease resistance
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. It is necessary to recover the untapped variability of wild tomato relatives, as they represent the primary source of resistance for the cultivated tomato, being rich in genes conferring resistance to a large panel of pathogens [10]. The identification and characterization of resistance (R)-genes in tomato wild relatives is definitely useful for both classical and innovative breeding strategies. In ETI, immunity is mainly activated through the recognition of pathogen effectors via plant disease R-proteins. NB-LRR helpers turned out to be essential in tomato, to support the activity of NB-LRR sensors, and to counteract plant pathogens that evolve quickly, increasing the robustness of the innate immune system [23,24]. The information on R-genes gathered so far in major Solanaceae crops and wild tomato relatives set the stage to develop innovative genomic-driven breeding strategies, aimed to furnish novel resistance sources
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