Identification of I ‐7 expands the repertoire of genes for resistance to F usarium wilt in tomato to three resistance gene classes

Summary The tomato I ‐3 and I ‐7 genes confer resistance to F usarium oxysporum f. sp. lycopersici ( F ol ) race 3 and were introgressed into the cultivated tomato, S olanum lycopersicum , from the wild relative S olanum pennellii . I‐3 has been identified previously on chromosome 7 and encodes an S ‐receptor‐like kinase, but little is known about I ‐7 . Molecular markers have been developed for the marker‐assisted breeding of I ‐3 , but none are available for I ‐7. We used an RNA ‐seq and single nucleotide polymorphism ( SNP ) analysis approach to map I ‐7 to a small introgression of S . pennellii   DNA ( c . 210 kb) on chromosome 8, and identified I ‐7 as a gene encoding a leucine‐rich repeat receptor‐like protein ( LRR‐RLP ), thereby expanding the repertoire of resistance protein classes conferring resistance to F ol . Using an eds1 mutant of tomato, we showed that I ‐7, like many other LRR ‐ RLPs conferring pathogen resistance in tomato, is EDS 1 (Enhanced Disease Susceptibility 1) dependent. Using transgenic tomato plants carrying only the I ‐7 gene for F ol resistance, we found that I ‐7 also confers resistance to F ol races 1 and 2. Given that F ol race 1 carries A vr1 , resistance to F ol race 1 indicates that I ‐7‐mediated resistance, unlike I ‐2‐ or I ‐3‐mediated resistance, is not suppressed by A vr1. This suggests that A vr1 is not a general suppressor of F ol resistance in tomato, leading us to hypothesize that A vr1 may be acting against an EDS1‐independent pathway for resistance activation. The identification of I ‐7 has allowed us to develop molecular markers for marker‐assisted breeding of both genes currently known to confer F ol race 3 resistance ( I ‐3 and I ‐7 ). Given that I ‐7‐mediated resistance is not suppressed by A vr1, I ‐7 may be a useful addition to I ‐3 in the tomato breeder's toolbox.