Magnaporthe oryzae pathotype Triticum (MoT) can act as a heterologous expression system for fungal effectors with high transcript abundance in wheat

Abstract

Plant pathogens deliver effector proteins to reprogramme a host plants circuitry, supporting their own growth and development, whilst thwarting defence responses. A subset of these effectors are termed avirulence factors (Avr) and can be recognised by corresponding host resistance (R) proteins, creating a strong evolutionary pressure on pathogen Avr effectors that favours their modification/deletion to evade the immune response. Hence, identifying Avr effectors and tracking their allele frequencies in a population is critical for understanding the loss of host recognition. However, the current systems available to confirm Avr effector function, particularly for obligate biotrophic fungi, remain limited and challenging. Here, we explored the utility of the genetically tractable wheat blast pathogen Magnaporthe oryzae pathotype Triticum (MoT) as a suitable heterologous expression system in wheat. Using the recently confirmed wheat stem rust pathogen (Puccina graminis f. sp. tritici) avirulence effector AvrSr50 as a proof-of-concept, we found that delivery of AvrSr50 via MoT could elicit a visible Sr50-dependant cell death phenotype. However, activation of Sr50-mediated cell death correlated with a high transgene copy number and transcript abundance in MoT transformants. This illustrates that MoT can act as an effective heterologous delivery system for fungal effectors from distantly related fungal species, but only when enough transgene copies and/or transcript abundance is achieved.

The wheat powdery mildew resistance gene Pm4 also confers resistance to wheat blast

“…This makes NO6047 an ideal isolate to host the effector AVR-Rmg8 . Isolate NO6047 is virulent on wheat line S-615, which carries Rmg8 , whereas isolate NO6047 + AVR8 is not virulent because of host recognition of AVR-Rmg8 17 . The resistance of wheat accessions showing resistance to NO6047 + AVR8 but not to NO6047 were assumed to be due to recognition of the AVR-Rmg8 effector.…”

“…1), despite them both carrying the 2NS resistance 15,16 . The second isolate (NO6047 + AVR-Rmg8) (henceforth referred to as NO6047 + AVR8) is a derivative of isolate NO6047 that was transformed with allele eI of AVR-Rmg8 under control of the PWL2 promoter 17 (Supplementary Table 2). NO6047 contains an alternative allele of the AVR-Rmg8 effector, designated eII′′′, which is not recognized by Rmg8 13 .…”

Multiplexed effector screening for recognition by endogenous resistance genes using positive defense reporters in wheat protoplasts

“…We used the wheat cultivar (cv) Fielder for the analysis of AvrSr35/Sr35 and expressed both genes from a plasmid. For AvrSr50/Sr50 , we made use of the introgression of Sr50 into cv Gabo (GaboSr50) and generated protoplast from cv Gabo and cv GaboSr50 (Jensen & Saunders, 2023). We only expressed AvrSr50 from a plasmid.…”

The wheat powdery mildew resistance genePm4also confers resistance to wheat blast

“…1 ), despite them both carrying the 2NS resistance (Walkowiak et al 2020; Ferreira et al 2020). The second isolate (NO6047+ AVR-Rmg8 ), (henceforth referred to as NO6047+ AVR8 ) is a derivative of isolate NO6047 that was transformed with allele eI of AVR-Rmg8 under control of the PWL2 promoter (Jensen and Saunders 2023) ( Supplementary Table 2 ). NO6047 contains an alternative allele of the AVR-Rmg8 effector, designated eII’’’ , which is not recognised by Rmg8 (Latorre et al 2023).…”

“…This makes NO6047 an ideal isolate to host the effector Avr-Rmg8 . Isolate NO6047 is virulent on wheat line S-615 which carries Rmg8 whereas isolate NO6047+ AVR8 is not virulent because of host recognition of AVR-Rmg8 (Jensen and Saunders 2023). The resistance of any wheat accessions showing resistance to NO6047+ AVR-Rmg8 but not to NO6047 can be assumed to be due to recognition of the AVR8-Rmg8 effector.…”