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Genetic Basis for the Hierarchical Interaction Between Tobamovirus spp. and L Resistance Gene Alleles from Different Pepper Species

The pepper L gene conditions the plant's resistance to Tobamovirus spp. Alleles L¹, L², L³, and L⁴ confer a broadening spectra of resistance to different virus pathotypes. In this study, we report the genetic basis for the hierarchical interaction between L genes and Tobamovirus pathotypes. We cloned L³ using map-based methods, and L¹, L^1a, L^1c, L², L^2b, and L⁴ using a homology-based method. L gene alleles encode coiled-coil, nucleotide-binding, leucine-rich repeat (LRR)-type resistance proteins with the ability to induce resistance response to the viral coat protein (CP) avirulence effectors by themselves. Their different recognition spectra in original pepper species were reproduced in an Agrobacterium tumefaciens–mediated transient expression system in Nicotiana benthamiana. Chimera analysis with L¹, which showed the narrowest recognition spectrum, indicates that the broader recognition spectra conferred by L², L^2b, L³, and L⁴ require different subregions of the LRR domain. We identified a critical amino acid residue for the determination of recognition spectra but other regions also influenced the L genes' resistance spectra. The results suggest that the hierarchical interactions between L genes and Tobamovirus spp. are determined by the interaction of multiple subregions of the LRR domain of L proteins with different viral CP themselves or some protein complexes including them.