Fusarium graminearum KP4-like proteins possess root growth-inhibiting activity against wheat and potentially contribute to fungal virulence in seedling rot

Authors: Lu, Shunwen; Faris, Justin

Submitted to: Fungal Genetics and Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/8/2018
Publication Date: 2/1/2019
Publication URL: https://handle.nal.usda.gov/10113/6230277
Citation: Lu, S., Faris, J.D. 2019. Fusarium graminearum KP4-like proteins possess root growth-inhibiting activity against wheat and potentially contribute to fungal virulence in seedling rot. Fungal Genetics and Biology. 123:1-13. https://doi.org/10.1016/j.fgb.2018.11.002.
DOI: https://doi.org/10.1016/j.fgb.2018.11.002

Interpretive Summary: Fusarium head blight (FHB) is a devastating disease of wheat and barley worldwide. In addition to infecting the heads of the plants, the fungus that causes FHB also lives in the soil and can cause root rot of wheat. This study was conducted to identify and characterize proteins in the fungus that contribute to the ability of the pathogen to cause FHB and other diseases of wheat. Four proteins with high levels of similarity to each other were identified in the FHB-causing fungus, and they were highly similar to a toxic protein that was first identified in the fungus that causes the disease known as corn smut. One of the FHB fungus proteins inhibited root growth of wheat seedlings. When the genes that encode three of the four proteins were deleted, the ability of the fungus to cause root rot was diminished. However, even without the three proteins, the fungus could still cause FHB on wheat heads indicating that the proteins were important for the fungus to cause root rot, but not for causing FHB. Additional analysis indicated that many species contain similar proteins that are involved in pathogenesis, including human pathogens.

Technical Abstract: The virally encoded KP4 killer toxin protein was first identified from Ustilago maydis (Um), and its homologues are present in diverse fungi and in one species of moss. No KP4-like (KP4L) proteins have been functionally characterized. Here, we report the identification and functional analysis four KP4L proteins from Fusarium graminearum (Fg), the primary causal pathogen of Fusarium head blight (FHB), which is also known to associate with seedling rot of wheat. The four FgKP4L proteins (FgKP4L-1, -2, -3 and -4) are encoded by small open reading frames (378-825 bp) located on chromosome 1 with the FgKP4L-1, -2 and -3 genes clustering together. Sequence analysis indicated that FgKP4L proteins have conserved domains predicted to form a three-dimensional alpha/beta-sandwich structure as first reported for UmKP4. with FgKP4L-4 featuring double Kp4 domains. Transcriptional analysis revealed that the FgKP4L genes are expressed in vitro under certain stress conditions, and all up-regulated during FHB and/or seedling rot development. Plant assays indicated the recombinant FgKP4L-2 protein does not induce cell death in wheat leaves or spikelets, but inhibits root growth of young seedlings. Targeted gene deletion confirmed that elimination of the FgKP4L-1/-2/-3 gene cluster from the fungal genome results in reduced virulence in seedling rot but not in FHB. Database searches revealed KP4L proteins from ~80 fungal species with the majority (>70%) belonging to Sordiromycetes. Phylogenetic analysis suggested that UmKP4 and the moss KP4L proteins are closely related to those from a zygromycete and Aspergillus, respectively, implying cross-kingdom horizontal gene transfer.