Phytophthora RxLR effector Pi18609 suppresses host immunity by promoting turnover of a positive immune regulator StBBX27.

Oomycete pathogens deliver a number of RxLR effector proteins into host plant cells to manipulate immunity by targeting diverse host proteins. Here, we reveal that a Phytophthora infestans RxLR effector Pi18609 targets a potato B-box transcription factor (BBX), StBBX27, which was identified to positively regulate late blight resistance. Silencing the ortholog NbBBX27 in Nicotiana benthamiana or RNA interfering StBBX27 in potato increases host colonization by P.