Differential Regulation and Posttranslational Processing of the Class II Hydrophobin Genes from the Biocontrol FungusHypocrea atroviridis

Abstract

Hydrophobins are small extracellular proteins, unique to and ubiquitous in filamentous fungi, which mediate interactions between the fungus and environment. The mycoparasitic fungus Hypocrea atroviridis has recently been shown to possess 10 different class II hydrophobin genes, which is a much higher number than that of any other ascomycete investigated so far. In order to learn the potential advantage of this hydrophobin multiplicity for the fungus, we have investigated their expression patterns under different physiological conditions (e.g., vegetative growth), various conditions inducing sporulation (light, carbon starvation, and mechanical injury-induced stress), and confrontation with potential hosts for mycoparasitism. The results show that the 10 hydrophobins display different patterns of response to these conditions: one hydrophobin (encoded by hfb-2b) is constitutively induced under all conditions, whereas other hydrophobins were formed only under conditions of carbon starvation (encoded by hfb-1c and hfb-6c) or light plus carbon starvation (encoded by hfb-2c, hfb-6a, and hfb-6b). The hydrophobins encoded by hfb-1b and hfb-5a were primarily formed during vegetative growth and under mechanical injury-provoked stress. hfb-22a was not expressed under any conditions and is likely a pseudogene. None of the 10 genes showed a specific expression pattern during mycoparasitic interaction. Most, but not all, of the expression patterns under the three different conditions of sporulation were dependent on one or both of the two blue-light regulator proteins BLR1 and BLR2, as shown by the use of respective loss-of-function mutants. Matrix-assisted laser desorption ionization-time of flight mass spectrometry of mycelial solvent extracts provided sets of molecular ions corresponding to HFB-1b, HFB-2a, HFB-2b, and HFB-5a in their oxidized and processed forms. These in silico-deduced sequences of the hydrophobins indicate cleavages at known signal peptide sites as well as additional N-and C-terminal processing. Mass peaks observed during confrontation with plant-pathogenic fungi indicate further proteolytic attack on the hydrophobins. Our study illustrates both divergent and redundant functions of the 10 hydrophobins of H. atroviridis.

Hydrophobin genes of the entomopathogenic fungus, Metarhizium brunneum, are differentially expressed and corresponding mutants are decreased in virulence

“…Interestingly, none of the hydrophobin genes was expressed in 3-day-old mycelium in liquid culture, although HYD1 was seen in mycelium grown on solid medium. In Hypocrea atroviridis, diVerential expression patterns were dependent on diVerent physiological conditions for the ten diVerent class II hydrophobin genes, and there appeared to be both divergent and redundant patterns among HYD genes (Mikus et al 2009). Fang et al (2007) showed that a M. anisopliae G protein signaling (RGS) protein, cag8, aVects ssgA/HYD1 expression; transcript levels were markedly reduced in cag8 gene mutants and they also lost pigmentation in liquid culture.…”

Translational Research on Trichoderma: From 'Omics to the Field

“…Of those, 60% were from the eukaryotic orthologous groups (KOGs) involved in the cell processes of post-translational modification (HSPs, aspartyl protease, serine protease, glutathione peroxidase, ATPase), and amino acid and lipid metabolism. The most abundantly expressed genes encoded the CPC1 transcription factor (7); a type II hydrophobin (85); a glyceraldehyde 3-phosphate dehydrogenase highly represented in EST collections of T. reesei (32), T. harzianum (140), and T. longibrachiatum (141); an enolase, also identified in the interaction proteome of T. harzianum (50), involved in thermal tolerance, glycerol synthesis, and salt stress. In addition, genes encoding aspartyl and subtilin-like serine proteases were found to be highly expressed in different EST collections of biocontrol strains (73,118,141), which supports the hypothesis of their involvement in the first stages of mycoparasitism (96,98,123).…”

The Genomes of Three Uneven Siblings: Footprints of the Lifestyles of Three Trichoderma Species

“…Hydrophobins are small secreted proteins, found in the outer surface of the cell wall of hyphae and conidia. In this regard, hfb-2c, hfb-6a, and hfb-6b are expressed in T. atroviride under the conditions and time at which conidia are observed (1088). In T. reesei, expression of plant cell wall-degrading enzymes was found to be a major event during conidiation (352).…”

“…Recently, a novel subclass of hydrophobins was proposed for Trichoderma (27). The 10 T. atroviride hydrophobin genes are expressed in response to various conditions, including exposure to light pulses, starvation, and injury, but do not show mycoparasitism-specific regulation patterns (1088). Moreover, T. reesei hfb1 (TR_73173, TA_258206, and TV_60531) and hfb2 (TR_119989, TA_258295, and TV_91466) are regulated in response to light and by the G-protein alpha-subunit GNA1 (617).…”