Gene Expression During Acibenzolar-S-Methyl-Induced Priming for Potentiated Responses to Venturia nashicola in Japanese Pear

Pretreatment of leaves of the Japanese pear plant with the synthetic SAR activator acibenzolar-S-methyl (ASM) significantly reduced the severity of scab caused by the fungal pathogen Venturia nashicola. In this study, we have cloned three defence-related genes that are involved in the signalling network from Japanese pear, including a non-expresser of pathogenesis-related protein 1 (jpNPR1), a respiratory burst oxidase homologues (jpRBOH) and a mitogen-activated protein kinase (jpMAPK). We studied their expression in the same conditions that allow protection afforded by ASM, using quantitative real-time reverse transcription-polymerase chain reaction (RT-PCR). Transcript level of jpNPR1 was not significantly elevated in Japanese pear leaves upon treatment with ASM and during infection with V. nashicola, and was highly and transiently primed in ASM-treated leaves after scab inoculation. Transcripts encoding jpRBOH and jpMAPK were directly responsive to ASM and were also early potentiated after pathogen inoculation. Involvement of NPR1 and reactive oxygen species in ASM-induced priming or potentiation is discussed.