The Hydrophobin-Like OmSSP1 May Be an Effector in the Ericoid Mycorrhizal Symbiosis

Abstract

Mutualistic and pathogenic plant-colonizing fungi use effector molecules to manipulate the host cell metabolism to allow plant tissue invasion. Some small secreted proteins (SSPs) have been identified as fungal effectors in both ectomycorrhizal and arbuscular mycorrhizal fungi, but it is currently unknown whether SSPs also play a role as effectors in other mycorrhizal associations. Ericoid mycorrhiza is a specific endomycorrhizal type that involves symbiotic fungi mostly belonging to the Leotiomycetes (Ascomycetes) and plants in the family Ericaceae. Genomic and RNASeq data from the ericoid mycorrhizal fungus Oidiodendron maius led to the identification of several symbiosis-upregulated genes encoding putative SSPs. OmSSP1, the most highly symbiosis up-regulated SSP, was found to share some features with fungal hydrophobins, even though it lacks the Pfam hydrophobin domain. Sequence alignment with other hydrophobins and hydrophobin-like fungal proteins placed OmSSP1 within Class I hydrophobins. However, the predicted features of OmSSP1 may suggest a distinct type of hydrophobin-like proteins. The presence of a predicted signal peptide and a yeast-based signal sequence trap assay demonstrate that OmSSP1 is secreted. OmSSP1 null-mutants showed a reduced capacity to form ericoid mycorrhiza with Vaccinium myrtillus roots, suggesting a role as effectors in the ericoid mycorrhizal interaction.

EffHunter: A Tool for Prediction of Effector Protein Candidates in Fungal Proteomic Databases

“…EffHunter predicted a similar number of effectors in ectomycorrhizal as in white and brown rots. In congruence with these findings, recent literature evidences that small-secreted effectors participate in all types of microbial interactions, and the concept "effector" seems to be rapidly evolving [67][68][69][70][71][72]. In Figure 3, the graphic shows the number of effectors predicted in different types of fungi: yeast, brown and white rot fungi, ectomycorrhiza, opportunistic, mycoparasites, human pathogens, plant pathogens, entomopathogens and saprotrophs (Supplementary Table S4).…”

Extracellular Vesicles from Fusarium graminearum Contain Protein Effectors Expressed during Infection of Corn

“…Germlings from Fgr mutants lacking FgHyd3 bind poorly to hydrophobic surfaces, such as plant leaves, and are not as infectious [55]. Other fungal hydrophobins have effector activity [56,57], hence it is possible that FgHyd3 also has effector activity, but this needs to be confirmed experimentally. The observation that FgHyd3 was exclusive to the EV samples suggests that EVs function as an unconventional secretion mechanism for some classes of protein effectors, that EVs could transport FgHyd3 to other areas of the plant, or that EVs shield it from early recognition by the plant's defenses.…”

Selection and Evaluation of Reference Genes for ddPCR-Based Transcript Abundance Studies in Oidiodendron Maius Across Varying Carbon Sources

“…The remainder were poorly characterized with only a general function predicted. Other than the aforementioned tubulin genes, this shortlist did not contain any of the transcripts typically considered housekeeping genes, nor those previously suggested for use as reference genes in qPCR of O. maius (46)(47)(48)(49). This absence of typical housekeeping genes supports the need to validate reference genes in the context of each experimental system.…”