Aspergillus Hydrophobins: Physicochemical Properties, Biochemical Properties, and Functions in Solid Polymer Degradation

Hydrophobins are small amphipathic proteins conserved in filamentous fungi. In this review, the properties and functions of Aspergillus hydrophobins are comprehensively discussed on the basis of recent findings. Multiple Aspergillus hydrophobins have been identified and categorized in conventional class I and two non-conventional classes. Some Aspergillus hydrophobins can be purified in a water phase without organic solvents. Class I hydrophobins of Aspergilli self-assemble to form amphipathic membranes. At the air–liquid interface, RolA of Aspergillus oryzae self-assembles via four stages, and its self-assembled films consist of two layers, a rodlet membrane facing air and rod-like structures facing liquid. The self-assembly depends mainly on hydrophobin conformation and solution pH. Cys4–Cys5 and Cys7–Cys8 loops, disulfide bonds, and conserved Cys residues of RodA-like hydrophobins are necessary for self-assembly at the interface and for adsorption to solid surfaces. AfRodA helps Aspergillus fumigatus to evade recognition by the host immune system. RodA-like hydrophobins recruit cutinases to promote the hydrolysis of aliphatic polyesters. This mechanism appears to be conserved in Aspergillus and other filamentous fungi, and may be beneficial for their growth. Aspergilli produce various small secreted proteins (SSPs) including hydrophobins, hydrophobic surface–binding proteins, and effector proteins. Aspergilli may use a wide variety of SSPs to decompose solid polymers.

Epigenetic Regulation of Verticillium dahliae Virulence: Does DNA Methylation Level Play A Role?

Verticillium dahliae is the etiological agent of Verticillium wilt of olive. The virulence of Defoliating V. dahliae isolates usually displays differences and high plasticity. This work studied whether an epigenetic mechanism was involved in this plasticity. An inverse correlation between virulence and DNA methylation of protein-coding genes was found. A set of 831 genes was selected for their highly consistent inverse methylation profile and virulence in the five studied isolates. Of these genes, ATP-synthesis was highly represented, which indicates that the more virulent D isolates are, the more energy requirements they may have. Furthermore, there were numerous genes in the protein biosynthesis process: genes coding for the chromatin structure, which suggests that epigenetic changes may also affect chromatin condensation; many transmembrane transporter genes, which is consistent with denser compounds, traffic through membranes in more virulent isolates; a fucose-specific lectin that may play a role in the attachment to plant cell walls during the host infection process; and pathogenic cutinases that facilitate plant invasion and sporulation genes for rapid spreading alongside plants. Our findings support the notion that differences in the virulence of the Defoliating V. dahliae isolates may be controlled, at least to some extent, by an epigenetic mechanism.

Molecular evidence that the extracellular cutinase Pbc1 is required for pathogenicity of Pyrenopeziza brassicae on oilseed rape

Recent evidence has suggested that cutinase is required for cuticular penetration and, therefore, is essential for pathogenicity of Pyrenopeziza brassicae, the causal organism of light leaf spot disease of oilseed rape and other brassicas. In order to acquire molecular evidence for the role of cutinase in pathogenesis, the single-copy P. brassicae cutinase gene Pbc1 was disrupted by a transformation-mediated approach. Southern hybridization analysis revealed that in one mutant, NH10-1224, the disruption was due to a tandem insertion of two copies of the disruption vector into the 5' coding region of Pbc1. In contrast to the wild type, no expression of Pbc1 was detected during in planta growth or in cutin-induced mycelium of NH10-1224 and no cutinase activity was detected in culture supernatants from NH10-1224 using p-nitrophenyl butyrate as substrate. Scanning electron microscopy of Brassica napus cotyledons infected with wild-type P. brassicae confirmed that entry into the host is by direct penetration of the cuticle. In contrast, the cutinase-deficient mutant NH10-1224 failed to penetrate the cuticular layer and was unable to develop disease symptoms. This evidence is consistent with the hypothesis that Pbc1 is required for P. brassicae to penetrate the plant cuticle. Demonstration that complementation of NH10-1224 with the Pbc1 wild-type gene restores both cutinase activity and pathogenicity will be required to definitively establish that cutinase is required for successful pathogenesis of brassicas by P. brassicae.

Plant antioxidant gene responses to fungal pathogens

Antioxidant defense systems are a prominent element in plant responses to environmental stress. Activated oxygen species have themselves been implicated as both a part of the plant's defense against pathogen attack as well as the phytotoxic component of photosensitizing fungal toxins. Molecular analyses are just beginning to define how plant oxidant and antioxidant genes might integrate with other defense responses to provide effective protection against pathogen attack.

The role of cutinase in fungal pathogenicity

Cutinase, an extracellular fungal enzyme, is thought to be essential for the pathogenicity of certain fungal species to plants. Interpretations of recent data on fungal cutinase activity and pathogenicity are contradictory, and range from cutinase having no apparent influence on pathogenicity to it enhancing adhesion of fungal spores to the plant surface.