Hydrophobins contribute to root colonization and stress responses in the rhizosphere-competent insect pathogenic fungus Beauveria bassiana

Abstract

The hyd1/hyd2 hydrophobins are important constituents of the conidial cell wall of the insect pathogenic fungus Beauveria bassiana. This fungus can also form intimate associations with several plant species. Here, we show that inactivation of two Class I hydrophobin genes, hyd1 or hyd2, significantly decreases the interaction of B. bassiana with bean roots. Curiously, the ∆hyd1/∆hyd2 double mutant was less impaired in root association than Δhyd1 or Δhyd2. Loss of hyd genes affected growth rate, conidiation ability and oosporein production. Expression patterns for genes involved in conidiation, cell wall integrity, insect virulence, signal transduction, adhesion, hydrophobicity and oosporein production were screened in the deletion mutants grown in different conditions. Repression of the major MAP-Kinase signal transduction pathways (Slt2 MAPK pathway) was observed that was more pronounced in the single versus double hyd mutants under certain conditions. The ∆hyd1/∆hyd2 double mutant showed up-regulation of the Hog1 MAPK and the Msn2 transcription factor under certain conditions when compared to the wild-type or single hyd mutants. The expression of the bad2 adhesin and the oosporein polyketide synthase 9 gene was severely reduced in all of the mutants. On the other hand, fewer changes were observed in the expression of key conidiation and cell wall integrity genes in hyd mutants compared to wild-type. Taken together, the data from this study indicated pleiotropic consequences of deletion of hyd1 and hyd2 on signalling and stress pathways as well as the ability of the fungus to form stable associations with plant roots.

Intracellular accumulation and secretion of hydrophobin-enriched vesicles aid the rapid sporulation of molds

“…Located outside of the cell, HFBs assemble at hydrophobic/hydrophilic interfaces, modulate surface properties, and mediate a broad spectrum of fungal interactions with their environment 8 . In molds (Ascomycota), HFBs coat spores, thereby protecting against abiotic stresses 2,38,39 and supporting attachment to hosts or substrates 40 . Because molds can rapidly generate large amounts of spores 16 , HFBs must also be abundantly secreted.…”

Metarhizium robertsii ammonium permeases (MepC and Mep2) contribute to rhizoplane colonization and modulates the transfer of insect derived nitrogen to plants

“…The role of hydrophobins during initial interaction and virulence with plant hosts have been investigated in phytopathogenic and endophytic fungi [23,47–50]. Although Hyd3 was upregulated in Metarhizium- bean root transcriptome, the disruption of Hyd3 did not affect the rhizoplane or rhizospheric colonization ability of M .…”

“…Fungal mycelia was collected after 4 days by vacuum filtration and ~0.25 g of fungal mycelia was transferred to flasks containing 25 ml of bean root exudate (BRE) and potato dextrose broth (PDB). The haricot bean ( Phaseolus vulgaris , Ontario Seed Co Ltd., Ontario, Canada) root exudate was prepared as described [23]. Cultures were then incubated at room temperature (22°C) at 120 r.p.m and the fungal mycelia was then harvested from bean root exudate after 8 hours of incubation.…”

“…To quantify fungal association, barley roots were harvested from 10 and 20 day old plants. The amount of fungal association on barley roots was analyzed as described previously [23]. To examine the endophytic association, the harvested roots were first washed in water to remove the attached vermiculite.…”

The Thm1 Zn(II)2Cys6 transcription factor contributes to heat, membrane integrity and virulence in the insect pathogenic fungus Beauveria bassiana

“…Studies on these entomopathogenic fungi, typified by the members of the Metarhizium and Beauveria genera, are gradually being regarding as model systems applicable to uncovering fundamental aspects of fungal development, stress response and virulence, particularly as these fungi display shared and unique attributes in comparison to plant and animals pathogens (Lu and St Leger, 2016;Wang et al, 2016;Zeng et al, 2017). B. bassiana is both a broad host range insect pathogen and a plant mutualist (Boucias et al, 2018;Moonjely et al, 2018). Infection occurs via adhesion of fungal conidia to the cuticle of the insect and subsequent direct penetration of the exoskeleton (Ortiz-Urquiza and .…”