Allelic variation of the AvrSr۵۰ effector increased virulence of the Puccinia graminis f. sp. tritici on Sr۵۰-carrying wheat lines

Wheat stem rust, caused by the biotrophic pathogen Puccinia graminis f. sp. tritici (Pgt), is an important disease worldwide. To overcome host immunity, Pgt secretes several effectors, including AvrSr۳۵ and AvrSr۵۰. These effectors are recognized by resistant cultivars carrying corresponding receptors, resulting in incompatible reactions. In this study, we assessed the resistance of Sr۳۵- and Sr۵۰-carrying wheat monogenic lines to ۳۰ Pgt isolates through inoculation with urediospores of pure isolates. Virulence analyses were evaluated for resistant IF ۰-۲ and susceptible ۳-۴ reactions and revealed that Pgt۲۰-۶ and Pgt۲۰-۱۲ isolates showed increased virulence on the Sr۵۰-carrying line. The presence of AvrSr۳۵ and AvrSr۵۰ genes was assessed in the genome of all isolates through PCR. Visualization of amplified fragments on agarose gel confirmed the presence of AvrSr۳۵ and AvrSr۵۰ genes in the genome of all ۳۰ isolates. Despite the presence of Avr genes in all isolates, the lack of active recognition for two isolates on the Sr۵۰-carrying line suggested point mutations in their sequence. Sequencing analysis of AvrSr۵۰ confirmed an A۱۷۸T mutation unique to these two virulent isolates. Homology modeling based on the solved crystal structure of AvrSr۵۰ showed a nonsynonymous mutation at the protein surface that may be involved in the interaction with Sr۵۰ to escape from recognition. This study showed the constant genetic change of fungus and recalled the necessity of continuously monitoring the fungal population to take appropriate strategies in wheat breeding programs.

کلیدواژه ها:

polymorphism ، Homology modeling ، Effector ، Point mutation ، Virulence ، Wheat stem rust