In planta expression screens of Phytophthora infestans RXLR effectors reveal diverse phenotypes, including activation of the Solanum bulbocastanum disease resistance protein Rpi-blb2.
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.
Department of Plant Pathology, Ohio State University-Ohio Agricultural Research and Development Center, Wooster, Ohio 44691, USA.
Sang-Keun
SK
Oh
Carolyn
C
Young
Minkyoung
M
Lee
Ricardo
R
Oliva
Tolga O
TO
Bozkurt
Liliana M
LM
Cano
Joe
J
Win
Jorunn I B
JI
Bos
Hsin-Yin
HY
Liu
Mireille
M
van Damme
William
W
Morgan
Doil
D
Choi
Edwin A G
EA
Van der Vossen
Vivianne G A A
VG
Vleeshouwers
Sophien
S
Kamoun
D020418:Algal Proteins / Q000378:metabolism*; D000483:Alleles; D000595:Amino Acid Sequence; D016923:Cell Death; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D007113:Immunity, Innate; D008969:Molecular Sequence Data; D055750:Phytophthora infestans / Q000378:metabolism / Q000472:pathogenicity*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D011110:Polymorphism, Genetic; D018749:RNA, Plant / Q000378:metabolism; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D032322:Solanum / Q000235:genetics* / Q000276:immunology / Q000378:metabolism; D014026:Nicotiana / Q000235:genetics / Q000276:immunology / Q000378:metabolism
D020418:Algal Proteins; D010940:Plant Proteins; D018749:RNA, Plant