Sequence Variants of the Phytophthora sojae RXLR Effector Avr3a/5 Are Differentially Recognized by Rps3a and Rps5 in Soybean ; PLoS ONE

The perception of Phytophthora sojae avirulence (Avr) gene products by corresponding soybean resistance (Rps) gene products causes effector triggered immunity. Past studies have shown that the Avr3a and Avr5 genes of P. sojae are genetically linked, and the Avr3a gene encoding a secreted RXLR effector protein was recently identified. We now provide evidence that Avr3a and Avr5 are allelic. Genetic mapping data from F2 progeny indicates that Avr3a and Avr5 co-segregate, and haplotype analysis of P. sojae strain collections reveal sequence and transcriptional polymorphisms that are consistent with a single genetic locus encoding Avr3a/5. Transformation of P. sojae and transient expression in soybean were performed to test how Avr3a/5 alleles interact with soybean Rps3a and Rps5. Over-expression of Avr3a/5 in a P. sojae strain that is normally virulent on Rps3a and Rps5 results in avirulence to Rps3a and Rps5; whereas silencing of Avr3a/5 causes gain of virulence in a P. sojae strain that is normally avirulent on Rps3a and Rps5 soybean lines. Transient expression and cobombardment with a reporter gene confirms that Avr3a/5 triggers cell death in Rps5 soybean leaves in an appropriate allelespecific manner. Sequence analysis of the Avr3a/5 gene identifies crucial residues in the effector domain that distinguish recognition by Rps3a and Rps5. ; This work was supported by grants to MG from the Agriculture and Agri-Food Canada (AAFC) Crop Genomics Initiative; to SD from the National Natural Science Foundation of China (30900932); and to BMT from the Agriculture and Food Research Initiative of the USDA National Institute for Food and Agriculture, grant numbers 2007-35600-18530 and 2007-35319-18100, and from the US National Science Foundation (NSF), grant numbers MCB-0731969 and IOS-0924861. SD and DY were supported at AAFC by the China Scholarship Council. SDK was supported by an NSF pre-doctoral fellowship. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the ...