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The Magnaporthe oryzae Avirulence Gene AvrPiz-t Encodes a Predicted Secreted Protein That Triggers the Immunity in Rice Mediated by the Blast Resistance Gene Piz-t

¹National Center for Gene Research & Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200233, China; ²Key Laboratory of Biopesticide and Chemical Biology, Ministry of Education, Fujian Agriculture and Forestry University, Fuzhou 350002, China; ³Graduate School of the Chinese Academy of Sciences, Beijing 100049, China; ⁴Department of Plant Pathology, Nanjing Agriculture University, Nanjing 210095, China; ⁵Biotechnology Institute, Zhejiang University, Hangzhou 310029, China; ⁶Department of Plant Pathology, the Ohio State University, Columbus 43210, U.S.A.

The Magnaporthe oryzae avirulence gene AvrPiz-t activates immunity in a gene-for-gene fashion to rice mediated by the blast resistance gene Piz-t. To dissect the molecular mechanism underlying their recognition, we initiated the cloning of AvrPiz-t using a map-based cloning strategy. The AvrPiz-t gene was delimited to an approximately 21-kb genomic fragment, in which six genes were predicted. Complementation tests of each of these six candidate genes led to the final identification of AvrPiz-t, which encodes a 108-amino-acid predicted secreted protein with unknown function and no homologues in M. oryzae or in other sequenced fungi. We found that AvrPiz-t is present in the virulent isolate GUY11 but contains a Pot3 insertion at a position 462 bp upstream from the start codon. Complementation tests of AvrPiz-t genes driven by promoters of varying length revealed that a promoter larger than 462 bp is essential to maintain the AvrPiz-t function. These results suggest that a Pot3 insertion in GUY11 might interfere with the proper function of AvrPiz-t. Additionally, we found that AvrPiz-t can suppress the programmed cell death triggered by mouse BAX protein in Nicotiana benthamiana, identifying a mechanism by which AvrPiz-t may contribute virulence of M. oryzae.