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Deletion of the Phytophthora sojae Avirulence Gene Avr1d Causes Gain of Virulence on Rps1d

August 2013 , Volume 26 , Number  8
Pages  969 - 976

Ren Na,1,2 Dan Yu,1,3 Dinah Qutob,1 Jun Zhao,2 and Mark Gijzen1

1Agriculture and Agri-Food Canada, 1391 Sandford Street, London, ON, N5V 4T3, Canada; 2College of Agronomy, Inner Mongolia Agricultural University, Huhhot 010019, China; 3College of Plant Protection, Nanjing Agricultural University, Nanjing 210095, China

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Accepted 22 March 2013.

Phytophthora sojae is an oomycete and a pathogen of soybean that causes root rot. During infection P. sojae delivers effector proteins into host cells to foster disease. However, effector-triggered immunity (ETI) results when pathogen factors are recognized by host resistance (R) proteins. We have now identified the P. sojae Avr1d gene, which encodes a predicted effector protein with the amino acid motif Arg-X-Leu-Arg (RXLR). Genetic mapping of 16 different P. sojae isolates and of a segregating F2 population of 40 individuals shows that the predicted RXLR effector gene Avh6 precisely cosegregates with the Avr1d phenotype. Transient expression assays confirm that Avr1d triggers cell death specifically in Rps1d soybean plants. The Avr1d gene is present in P. sojae strains that are avirulent on Rps1d, whereas the gene is deleted from the genome of virulent strains. Two sequence variants of the Avr1d gene encoding different protein products occur in P. sojae strains, but both are recognized by Rps1d and cause ETI. Liposome binding assays show that Avr1d has affinity for phosphatidylinositol 4-phosphate and that binding can be disrupted by mutation of lysine residues in the carboxy-terminal effector domain of the protein. The identification of Avr1d aids pathogen diagnostics and soybean cultivar development.

This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 2013.