Molecular Investigation of <i>Rlm3</i> From Rapeseed as a Potential Broad‐Spectrum Resistance Gene Against Fungal Pathogens Producing Structurally Conserved Effectors

ABSTRACT Recognition of a pathogen avirulence (AVR) effector protein by its cognate plant resistance (R) protein triggers immune responses that are typically sufficient to provide effective disease control. While AVR effectors have long been considered species‐ or genotype‐specific, several studies have recently shown that these proteins belong to a limited set of structural families. This finding paves the way for the identification or engineering of broad‐spectrum R proteins capable of recognising several members of the same structural family. In the Leptosphaeria maculans– rapeseed ( Brassica napus ) pathosystem, 13 AVR genes have been cloned, of which four encode effectors belonging to the LARS ( Leptosphaeria AviRulence and Suppressing) structural family. Homologues of the L. maculans AvrLm3 AVR protein, a LARS family member, have been identified in other fungal species, including an AVR protein from Fulvia fulva , Ecp11‐1. We have previously shown that Ecp11‐1 is recognised by rapeseed varieties carrying the Rlm3 R gene, and that this recognition is masked in the presence of another LARS AVR gene, AvrLm4‐7 . In this study, we expanded our characterisation of the Rlm3 resistance spectrum to effectors from Fusarium oxysporum and Zymoseptoria ardabiliae . Like Ecp11‐1, we showed that an effector from F. oxysporum f. sp. narcissi is recognised by Rlm3, and that this recognition is masked in the presence of AvrLm4‐7 . We also investigated which protein regions and amino acids are necessary for AvrLm3 and Ecp11‐1 recognition by Rlm3. This analysis is a first step towards the identification of broad‐spectrum R proteins that confer protection against multiple phytopathogens.