Molecular characterization and functional analysis of PR-1-like proteins identified from the wheat head blight fungus Fusarium graminearum

Authors: Lu, Shunwen; Edwards, Michael

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/7/2017
Publication Date: 11/8/2017
Citation: Lu, S., Edwards, M.C. 2017. Molecular characterization and functional analysis of PR-1-like proteins identified from the wheat head blight fungus Fusarium graminearum. Phytopathology. 108:510-520. https://doi.org/10.1094/PHYTO-08-17-0268-R.
DOI: https://doi.org/10.1094/PHYTO-08-17-0268-R

Interpretive Summary: Fusarium head blight (FHB) is a devastating disease of wheat crops worldwide. The primary cause of FHB is Fusarium graminearum, a fungal pathogen that also produces a number of mycotoxins harmful to humans and animals. The underlying mechanisms controlling pathogenicity and virulence of this fungus are still not well understood. Thus, the major goal of this study was to learn more about a group of proteins that may affect the virulence of this fungus and its ability to cause disease. More specifically, we characterized F. graminearum proteins that have similarities to a group of proteins known as the plant group 1 pathogenesis-related (PR-1) proteins, which are known to be involved in the interactions between pathogens and plants. Four PR-1-like proteins were identified from the genome of the fungus and genomic structures and expression patterns of the corresponding genes were determined. PR-1-like proteins were also identified from other fungi that infect plants, and evolutionary relationships between these proteins were examined. Mutants of the fungus that lacked individual PR-1-like genes were created and tested for how well they could cause disease on susceptible wheat. It was found that deletion of one of the PR-1-like genes from the fungal genome results in significantly reduced virulence on wheat. This study provides the first example that a fungal PR-1-like protein contributes to virulence associated with FHB disease.

Technical Abstract: The group 1 pathogenesis-related (PR-1) proteins originally identified from plants and their homologues are also found in other eukaryotic kingdoms. Studies on non-plant PR-1-like (PR-1L) proteins have been pursued widely in humans/animals but rarely in filamentous ascomycetes. Here we report the characterization of four PR-1L proteins identified from the ascomycete fungus Fusarium graminearum, the primary cause of Fusarium head blight of wheat and barley. Molecular cloning revealed that the four FgPR-1L proteins are all encoded by small open reading frames (612 to 909 bp) that are often interrupted by introns, in contrast to plant PR-1 genes that lack introns. Sequence analysis indicated that all FgPR-1L proteins contain the PR-1-specific three-dimensional structure, and one of them features a C-terminal transmembrane (TM) domain that has not been reported for any stand-alone PR-1 proteins. Transcriptional analysis revealed that the four FgPR-1L genes are expressed in axenic cultures and in planta with different spatial/temporal expression patterns. Phylogenetic analysis indicated that fungal PR-1L proteins fall into three major groups, one of which harbors FgPR-1L-2-related TM-containing proteins from both phytopathogenic and human-pathogenic ascomycetes. Low-temperature SDS-PAGE and proteolytic assays indicated that the recombinant FgPR-1L-4 protein exists as a monomer and is resistant to subtilisin of the serine protease family. Functional analysis confirmed that deletion of the FgPR-1L-4 gene from the fungal genome results in significantly reduced virulence on susceptible wheat. This study provides the first example that the F. graminearum–wheat interaction involves a pathogen-derived PR-1-like protein that affects fungal virulence on the host.