Abstract
Magnaporthe oryzae infects rice, wheat, and many grass species in the Poaceae family by secreting protein effectors. Here, we analyzed the distribution, sequence variation, and genomic context of effector candidate (EFC) genes in 31 isolates that represent five pathotypes of M. oryzae, three isolates of M. grisea, a sister species of M. oryzae, and one strain each for eight species in the family Magnaporthaceae to investigate how the host range expansion of M. oryzae has likely affected the evolution of effectors. We used the EFC genes of M. oryzae strain 70-15, whose genome has served as a reference for many comparative genomics analyses, to identify their homologs in these strains. We also analyzed the previously characterized avirulence (AVR) genes and single-copy orthologous (SCO) genes in these strains, which showed that the EFC and AVR genes evolved faster than the SCO genes. The EFC and AVR repertoires among M. oryzae pathotypes varied widely probably because adaptation to individual hosts exerted different types of selection pressure. Repetitive DNA elements appeared to have caused the variation of some EFC genes. Lastly, we analyzed expression patterns of the AVR and EFC genes to test the hypothesis that such genes are preferentially expressed during host infection. This comprehensive dataset serves as a foundation for future studies on the genetic basis of the evolution and host specialization in M. oryzae.
Highlights
Like other groups of plant pathogens, fungal pathogens secrete diverse effector proteins to manipulate host defense signaling pathways and downstream machinery
We mined the genes homologous to the previously characterized avirulence genes (AVRs) (Table 1) and effector candidate genes (EFCs) (Kim et al, 2016) genes from the genomes of 31 isolates corresponding to five pathotypes of M. oryzae
A phylogenomic tree built using 2,245 single-copy orthologous genes (SCOs) genes shows the clustering of M. oryzae isolates into monophyletic clades corresponding to the host of origin, and M. grisea isolates are distinct from the M. oryzae isolates (Figure 1A)
Summary
Like other groups of plant pathogens, fungal pathogens secrete diverse effector proteins to manipulate host defense signaling pathways and downstream machinery. Evolution of Magnaporthe Effector Genes each strain, including both the virulence and AVR effectors, determines its host specialization (Sánchez-Vallet et al, 2018). Pathogens likely need to change their effector repertoire to infect a new host. Such changes include the acquisition of new effector gene(s), optimization of existing effectors for the new host, and modification of specific AVR genes in ways to avoid host recognition (Sánchez-Vallet et al, 2018). We analyzed the genomes of diverse strains that represent multiple host-specific groups (=pathotypes) of Magnaporthe oryzae, a fungal pathogen that infects important cereals, and related species to investigate how both types of effectors are distributed and have evolved
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