Evaluation of Pathogen-Protein Effectors Candidates Responsible for Triggering the Sr35-mediated Response to Puccinia graminis f. sp. tritici (Pgt) Infection

The Sr35 resistant gene (R) confers near-immunity to the new highly virulent Pgt race Ug99 group, which represents a serious threat to the worldwide wheat cropping system. During infection, Pgt like other pathogens, secrete proteins known as avr (avirulence) or effector proteins that facilitate the pathogen infection. Plant immunity occurs when a R gene recognize the effector (avr) inducing an immune response know as effector-triggered immunity (ETI) that results in localized apoptosis or hypersensitivity response limiting the pathogen proliferation.  Despite the essential role of  effectors in Pgt infection only a handful of effectors in Pucciniales order have been characterized. Moreover, specific effectors for Ug99 have not been characterized yet, delaying the progress in understanding the R-avr interaction in the Pgt-wheat pathosystem. We are using functional approaches based in the bacterial effector deliver system EtHAn (effector-to-host analyzer) to validate in planta a set of nine candidate effectors. Those candidate effectors were selected based on presence absence variation of genes that code for secretory proteins, after a comparative genomic analyses between Sr35 -virulent and avirulent groups of Pgt races. In parallel we generated several EMS (ethyl-methanesulfonate) mutants from the avirulent Pgt race RQKKC which were able to overcome the resistance provide by Sr35. By using the bacterial effector deliver system and comparative genomic analysis between Sr35-virulent mutants and RQKKC race, we expect to identify the effector(s) that are recognized by Sr35 and understand better the molecular interaction in Pgt-wheat pathosystem which will be translate in practical applications for crop protection and plant breeding.