Effector proteins from Phytophthora plant pathogens; delivery to host plant cells, and deployment in diverse Phytophthora species

One of the greatest recorded impacts of crop disease on human society was due to epidemics of late
blight disease on European potato crops in the 19 th century, most notably in Ireland. Late blight is
caused by the eukaryotic microbe, Phytophthora infestans, which today is still regarded as the most
serious disease of potato crops. For nearly 20 years, a major focus of the Phytophthora research
community has been on identifying secreted pathogen proteins, called effectors, that facilitate
disease development. Prominent among these is a large group that possess conserved N-terminal
RxLR and EER peptide motifs. These motifs have been postulated to mediate translocation of these
effectors inside plant cells where they act to subvert plant immune responses, but the mechanism of
effector translocation has yet to be determined. Using fluorescently tagged effectors delivered from
P. infestans, we have identified the involvement of a non-conventional protein secretion route for
the RxLR effectors. We are now working towards further characterisation of the secretion pathway
used by RxLR effectors, as part of a wider research programme to elucidate how this group of
effectors enters plant cells.

The second part of this seminar will focus on the deployment of effector proteins by other species of
Phytophthora. While much of the research into Phytophthora species has been directed at a few
crop infecting species such as P. infestans, other species from the genus that cause damage to
woody host plants are not as well investigated. We have been sequencing genomes and
transcriptomes from tree infecting species of Phytophthora, especially P. kernoviae and P. plurivora,
to determine if these species use a different repertoire of effectors to facilitate disease development
on woody host plants. From these initial experiments, insights into P. kernoviae and P. plurivora
pathogenicity will be presented.

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