The ACE1 secondary metabolite gene cluster is a pathogenicity factor of wheat blast fungus.

Wheat blast caused by Pyricularia oryzae pathotype Triticum is now becoming a very serious threat to global food security. Here, we report an essential pathogenicity factor of the wheat blast fungus that is recognized and may be targeted by a rice resistance gene. Map-based cloning of Pwt2 showed that its functional allele is the ACE1 secondary metabolite gene cluster of the wheat blast fungus required for its efficient penetration of wheat cell walls. ACE1 is required for the strong aggressiveness of Triticum, Eleusine, and Lolium pathotypes on their respective hosts, but not for that of Oryza and Setaria pathotypes on rice and foxtail millet, respectively. All ACE1 alleles found in wheat blast population are recognized by a rice resistance gene, Pi33, when introduced into rice blast isolates. ACE1 mutations for evading the recognition by Pi33 do not affect the aggressiveness of the rice blast fungus on rice but inevitably impair the aggressiveness of the wheat blast fungus on wheat. These results suggest that a blast resistance gene already defeated in rice may be revived as a durable resistance gene in wheat by targeting an Achilles heel of the wheat blast fungus.

Evolution of the wheat blast fungus through functional losses in a host specificity determinant.

Wheat blast first emerged in Brazil in the mid-1980s and has recently caused heavy crop losses in Asia. Here we show how this devastating pathogen evolved in Brazil. Genetic analysis of host species determinants in the blast fungus resulted in the cloning of avirulence genes PWT3 and PWT4, whose gene products elicit defense in wheat cultivars containing the corresponding resistance genes Rwt3 and Rwt4 Studies on avirulence and resistance gene distributions, together with historical data on wheat cultivation in Brazil, suggest that wheat blast emerged due to widespread deployment of rwt3 wheat (susceptible to Lolium isolates), followed by the loss of function of PWT3 This implies that the rwt3 wheat served as a springboard for the host jump to common wheat.