Phytopathogenic oomycetes, such as Phytophthora infestans, potentially secrete many RxLR effector proteins into plant cells to modulate plant immune responses and promote colonization. However, the molecular mechanisms by which these RxLR effectors suppress plant immune responses are largely unknown. Here we describe an RxLR effector PITG_22798 (Gene accession: XM_002998349) that was upregulated during early infection of potato by P. infestans. By employment of agroinfiltration, we observed that PITG_22798 triggers cell death in Nicotiana benthamiana. Confocal microscopic examination showed that PITG_22798-GFP (Green Fluorescent Protein) located in the host nucleus when expressed transiently in N. benthamiana leaves. A nuclear localization signal (NLS) domain of PITG_22798 is important for nuclear localization and cell death-inducing activity. Sequence alignment and transient expression showed that PITG_22798 from diverse P. infestans isolates are conserved, and transient expression of PITG_22798 enhances P. infestans colonization of N. benthamiana leaves, which suggests that PITG_22798 contributes to P. infestans infection. PITG_22798-triggered cell death is dependent on SGT1-mediated signaling and is suppressed by the P. infestans avirulence effector 3b (AVR3b). The present research provides a clue for further investigation of how P. infestans effector PITG_22798 associates with and modulates host immunity.

Potato late blight, caused by Phytophthora infestans , is one of the major threats affecting the quality and output of potato all over the world. Reactive oxygen species (ROS) acted as a signal molecule to transmit signals in plants at the early stage of disease infection, and it could induce disease resistance of the plant, including potato late blight. Anionic peroxidases in many plants were reported to be involved in defense to disease. However, limited information about anionic peroxidase genes is available for the potato. Here, we reported that the expression of the StPOPA , a gene encoding a suberization-associated anionic peroxidase, was associated with resistance in potato against P. infestans. The StPOPA gene was induced by P. infestans infection, mechanical damage, jasmonic acid and ethylene treatment. Overexpression of the StPOPA gene in potato enhanced the resistance against P. infestans via promoting the accumulation of callose in the cell wall and ROS in the cytoplasm, which restricted the infection and spreading of the disease possibly by purposeful programmed cell death. Taken together, our results suggested that the StPOPA gene contributed to potato immunity against P. infestans and this gene could be used for the genetic improvement of resistance against potato late blight.