The DNA damage response in fungal plant pathogens

The ability to withstand UV damage shapes the ecology of microbes. While mechanisms of UV tolerance were extensively investigated in microorganisms regularly exposed to the sun, far less is known about UV repair of soilborne microorganisms. Fusarium oxysporum is a soilborne, fungal plant pathogen that is resistant to UV. We hypothesized that its UV repair capacity is induced to meet irregular sun exposure. Unlike the SOS paradigm, our analysis revealed only sporadic increases and even decreases in UV repair gene expression following UVC irradiation or exposure to visible light. Strikingly, a major factor determining the expression of UV repair genes was the developmental status of the fungus. At the early stages of germination the expression of photolyase increased while the expression of UV endonuclease decreased, then the trend was reversed. These gene expression oscillations were dependent on cell cycle progression. Consequently, the contribution of photoreactivation to UV repair and survival was stronger at the beginning of germination than later when a filament was established. F. oxysporum germinates following cues from the host. Early on germination it is most vulnerable to UV; when the filament is established the pathogen is protected from the sun because it is already within the host tissue.