Phytophthora infestans effector Pi14054 is a novel candidate suppressor of host silencing mechanisms

Phytophthora infestans is the oomycete pathogen responsible for the devastating late blight disease on potato and tomato. It can also infect the model solanaceous plant Nicotiana benthamiana. P. infestans secretes, and translocates into host cells, an array of RxLR class effectors potentially involved in diverse functions that facilitate infection of host plants. Intensive research efforts are currently focused on determining the role(s) of effectors in promoting late blight disease development, with many experiments carried out in the model plant N. benthamiana. In this study we demonstrate that candidate effector Pi14054 has activity as a suppressor of RNA silencing in N. benthamiana using an established reporter assay based on the Turnip crinkle virus - green fluorescent protein (TCV-sGFP) system. Pi14054 was able to complement TCV deficient for a viral suppressor of RNA silencing. This is a novel way to identify RNA silencing suppressors that potentially manipulate host immune responses. Transcripts encoding Pi14054 were most abundant during the first 36 h of infection development, suggesting that expression of this gene is specifically induced in contact with host tissue to modulate plant defences, as seen with other known effectors. Pi14054 is present in a diverse range of modern aggressive and hyper-aggressive European P. infestans isolates, suggesting a potential role for this effector in pathogenicity.