Potato pectin falls to Phytophthora: Phytophthora infestans is a plant oomycete pathogen that drove the potato famines of the 1800s and continues to afflict potato fields today. The polysaccharide pectin makes up about a third of the cell wall in potatoes. Sabbadin et al . identified a family of lytic polysaccharide monooxygenases (LMPOs) that cleave pectin and are upregulated in P. infestans during infection. Silencing the relevant LMPO gene successfully inhibited P. infestans infections. These findings open doors for disease intervention targets and for biotech applications. —PJH

The oomycete pathogen Aphanomyces astaci, also known as “crayfish plague”, is an obligate fungal-like parasite of freshwater crustaceans and is considered responsible for the ongoing decline of native European crayfish populations. A. astaci is thought to secrete a wide array of effectors and enzymes that facilitate infection, however their molecular mechanisms have been poorly characterized. Here, we report the identification of AA15 lytic polysaccharide monooxygenases (LPMOs) as a new group of secreted virulence factors in A. astaci. We show that this enzyme family has greatly expanded in A. astaci compared to all other oomycetes, and that it may facilitate infection through oxidative degradation of crystalline chitin, the most abundant polysaccharide found in the crustacean exoskeleton. These findings reveal new roles for LPMOs in animal–pathogen interactions, and could help inform future strategies for the protection of farmed and endangered species.

Phytophthora infestans is a damaging crop pathogen and a model oomycete for studying plant-pathogen interactions. We report the functional characterisation of a group of P. infestans berberine bridge enzyme-like proteins (BBEs) and their role in plant infection. We demonstrate that BBE-encoding genes are upregulated early during infection and that the secreted enzymes specifically oxidise fragments of pectin, the most abundant charged polysaccharide in the plant cell wall. We further show that these enzymes preferentially oxidise longer pectin fragments, which evade detection by the plant and fail to trigger reactive oxygen species (ROS) signalling. Microscopy revealed that the most abundant P. infestans BBE localises at germ tube tips prior to leaf penetration, and at haustoria during early infection. Combined with the reduced infection observed upon silencing of the encoding genes, these findings point to a key role for this enzyme class in host penetration and colonisation by microbial pathogens. The identification of BBEs as oomycete pathogenicity factors opens new opportunities for crop protection and food security.