In Planta Expression Screens ofPhytophthora infestansRXLR Effectors Reveal Diverse Phenotypes, Including Activation of theSolanum bulbocastanumDisease Resistance Protein Rpi-blb2

Abstract

The Irish potato famine pathogen Phytophthora infestans is predicted to secrete hundreds of effector proteins. To address the challenge of assigning biological functions to computationally predicted effector genes, we combined allele mining with high-throughput in planta expression. We developed a library of 62 infection-ready P. infestans RXLR effector clones, obtained using primer pairs corresponding to 32 genes and assigned activities to several of these genes. This approach revealed that 16 of the 62 examined effectors cause phenotypes when expressed inside plant cells. Besides the well-studied AVR3a effector, two additional effectors, PexRD8 and PexRD36 45-1 , suppressed the hypersensitive cell death triggered by the elicitin INF1, another secreted protein of P. infestans. One effector, PexRD2, promoted cell death in Nicotiana benthamiana and other solanaceous plants. Finally, two families of effectors induced hypersensitive cell death specifically in the presence of the Solanum bulbocastanum late blight resistance genes Rpi-blb1 and Rpi-blb2, thereby exhibiting the activities expected for Avrblb1 and Avrblb2. The AVRblb2 family was then studied in more detail and found to be highly variable and under diversifying selection in P. infestans. Structure-function experiments indicated that a 34-amino acid region in the C-terminal half of AVRblb2 is sufficient for triggering Rpi-blb2 hypersensitivity and that a single positively selected AVRblb2 residue is critical for recognition by Rpi-blb2.

An Effector-Targeted Protease Contributes to Defense against Phytophthora infestans and Is under Diversifying Selection in Natural Hosts

“…C14 was also found to interact with another effector protein of P. infestans, the host translocated RXLR effector AvrBlb2 (T. Bozkurt, S. Schornack, J. Win, and S. Kamoun, unpublished data; Oh et al, 2009). This indicates that different pathogen effectors target C14 and implies that C14 may also play a general role in immunity to bacterial and fungal diseases.…”

Evidence for intragenic recombination and selective sweep in an effector gene of Phytophthora infestans

“…These compensatory mutations have been widely documented (Jochumsen et al., 2016; Sato et al., 2016). Continuing genome expansion (Raffaele & Kamoun, 2012) may provide a unique environment for the development of compensatory mutations leading to functional redundancy or epitasis (Birch et al., 2008; Oh et al., 2009) in the effector genes of P. infestans .…”

The Effector SPRYSEC-19 ofGlobodera rostochiensisSuppresses CC-NB-LRR-Mediated Disease Resistance in Plants

“…We also coexpressed SPRYSEC-19 with R3a (Huang et al, 2005) and Rpi-blb2 (van der Vossen et al, 2005;Oh et al, 2009) from potato and their cognate elicitors from P. infestans in N. benthamiana leaves to test whether SPRYSEC-19 also modulates the cell death responses mediated by more distantly related CC-NB-LRR resistance proteins (see Supplemental Fig. S4 for an identity matrix).…”