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

Abstract

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 and, whose gene products elicit defense in wheat cultivars containing the corresponding resistance genes and 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 wheat (susceptible to isolates), followed by the loss of function of This implies that the wheat served as a springboard for the host jump to common wheat.

Transcription Factors Activate Genes through the Phase-Separation Capacity of Their Activation Domains

“…OCT4-MED1-IDR droplets were near-micron-sized (Figure S3B), exhibited fast recovery after photobleaching (Figure 3D), spherical shape (Figure S3C), and were salt sensitive (Figure 3E and S3D). Thus, they exhibited characteristics associated with phase-separated liquid condensates (Banani et al 2017; Shin et al 2017). Furthermore, we found that OCT4-MED1-IDR droplets could form in the absence of any crowding agent (Figure S3E and S3F).…”

“…The products of this type of protein-protein interaction, where the interaction interface cannot be described by a single conformation, have been termed “fuzzy complexes” (Tompa and Fuxreiter, 2008). These dynamic interactions are also typical of the IDR-IDR interactions that facilitate formation of phase-separated biomolecular condensates (Alberti, 2017; Banani et al, 2017; Hyman et al, 2014; Shin and Brangwynne, 2017; Wheeler and Hyman, 2018). …”

Wheat blast: from its origins in South America to its emergence as a global threat

“…Evidence supporting the hypothesis that wheat blast emerged via a host shift from a Pyricularia population infecting Lolium came from analyses of genetic variation in the avirulence genes PWT3 and PWT4 (Inoue et al ., ). In this model, Lolium‐ derived isolates carrying the Ao avirulence allele at the PWT3 locus infected a susceptible wheat cultivar carrying the rwt3 allele conditioning susceptibility, with the 1980s wheat blast outbreak in Brazil enabled by the widespread cultivation of susceptible wheat cultivars carrying rwt3 .…”

“…Later, selection on the less common Rwt3 wheat varieties favoured the emergence of pathogen strains with non‐functional PWT3 alleles. The model proposes that these pwt3 strains became the epidemic wheat blast population prevalent in South America (Inoue et al ., ). Although this model made use of available data, the study did not include any Lolium ‐associated populations of the pathogen from wheat blast endemic areas in Brazil, and did not consider that the association of Pyricularia with Lolium was reported 7 years after the Brazilian wheat blast outbreak (Igarashi et al ., ; Nunes et al ., ; Urashima et al ., ).…”

“…The broader host range and apparent genetic diversification of Pygt relative to P. oryzae raise many questions about the functional role of within‐species polymorphisms. Mutations in the avirulence genes PWT3 and PWT4 are the only genetic factors that have thus far been associated with adaptation of Pygt to its host, allowing the fungus to escape recognition (Inoue et al ., ). However, hundreds of presence/absence gene polymorphisms have been detected both within Pygt and between the wheat‐ and rice‐infecting populations (Chiapello et al ., ; Yoshida et al ., ).…”