Abstract
INTRODUCTION: NBS-LRR genes (NLRs) are the most extensive category of plant resistance genes (R genes) and play a crucial role in pathogen defense. Understanding the diversity and evolutionary dynamics of NLRs in different plant species is essential for improving disease resistance. This study investigates the NLR gene family in eight diploid wild strawberry species to explore their structural characteristics, evolutionary relationships, and potential for enhancing disease resistance. METHODS: We conducted a comprehensive genome-wide identification and structural analysis of NLRs across eight diploid wild strawberry species. Phylogenetic analysis was performed to examine the relationships between TIR-NLRs (TNLs), Non-TIR-NLRs (non-TNLs), CC-NLRs (CNLs), and RPW8-NLRs (RNLs). Gene structures were compared, and gene expression was profiled across different NLR subfamilies. Additionally, in vitro leaf inoculation assays with Botrytis cinerea were performed to assess the resistance of various strawberry species. RESULTS: Our analysis revealed that non-TNLs constitute over 50% of the NLR gene family in all eight strawberry species, surpassing the proportion of TNLs. Phylogenetic analysis showed that TNLs diverged into two subclades: one grouping with CNLs and the other closely related to RNLs. A significantly higher number of non-TNLs were under positive selection compared to TNLs, indicating their rapid diversification. Gene structure analysis demonstrated that non-TNLs have shorter gene structures than TNLs and exhibit higher expression levels, particularly RNLs. Notably, non-TNLs showed dominant expression under both normal and infected conditions. In vitro leaf inoculation assays revealed that Fragaria pentaphylla and Fragaria nilgerrensis, which have the highest proportion of non-TNLs, exhibited significantly greater resistance to Botrytis cinerea compared to Fragaria vesca, which has the lowest proportion of non-TNLs. DISCUSSION: The findings of this study provide important insights into the evolutionary dynamics of NLRs in strawberries, particularly the significant role of non-TNLs in pathogen defense. The rapid diversification and higher expression levels of non-TNLs suggest their potential contribution to enhanced disease resistance. This research highlights the value of non-TNLs in strawberry breeding programs aimed at improving resistance to pathogens such as Botrytis cinerea.