The response of P. infestans to fungicides and natural toxins

Our goal is to characterize the mechanism of toxin resistance in P. infestans. Two types of resistance are being studied: (i) resistance specific to a single type of fungicide, and (ii) broad-spectrum resistance (multifungicide resistance).

The fungicide metalaxyl used to be very effective against P. infestans worldwide. However, the emergence of resistance to this compound has led to major problems in controlling late blight.

Fungicides play a key role in controlling late blight, and consequently it is important to understand the basis of insensitivity to fungicides to slow the appearance of resistant strains. This is underscored by the negative consequences of resistance developed against the systemic fungicide, metalaxyl, which wreaked havoc in potato industry in the 1980s and 1990s. New systemic fungicides have been registered for late blight, including cymoxanil, dimethomorph, propamocarb, and strobilurins, however possible mechanisms of resistance to these newer compounds need to be addressed.

RNA blot analysis of selected ABC transporter genes in P. infestans; several are induced by fungicides.

Is is natural to expect that P. infestans has an inherent ability to resist the effects of toxins. Plant pathogens, including oomycetes, are exposed to a range of toxins during their life cycles; their survival today implies that they have an inherent ability to resist such substances. Pathogens evolved having to defend themselves against phytoalexins, antibiotics produced by competitors within the ecosystem, and abiotics naturally in the environment like heavy metals. Only recently have pathogens also been challenged by synthetic fungicides.

Even "sensitive" strains of P. infestans vary in their response to fungicides and toxins, such as those mentioned above. We hypothesize that such differences may be due to altered levels of expression (or activity) of ATP-binding cassette (ABC) transporter proteins. These proteins pump toxins out of the cytoplasm before they reach deleterious levels. ABC transporters are a normal component of all organisms and have been called an ancient cellular "immune" system against toxins.

Southern blot analysis of selected ABC transporter genes in P. infestans strains 618 (6) and 88069 (8); these proteins have been implicated as determinants of fungicide resistance.

We have identified the majority of ABC transporter genes from P. infestans and characterized their expression patterns in different isolates and in response to toxins. We are now dissecting the biochemical function of selected ABC transporter proteins.

Phylogram of ABC transporter superfamily of P. infestans.

Some of our publications on fungicide resistance can be viewed here.