A supprescin from a phytopathogenic fungus deactivates transcription of a plant defense gene encoding phenylalanine ammonia-lyase

Both elicitor and supprescin (suppressor) are present in the pycnospore germination fluid of a pea pathogen Mycospharella pinodes. A nuclear run-on assay revealed that supprescin rapidly deactivated elicitor-triggered transcription of the gene encoding phenylalanine ammonia-lyase in pea epicotyl tissues. The mechanism underlying the deactivation of the plant defense gene by signal molecules secreted from the fungal pathogen was investigated. Cis-acting sequences and trans-acting factors responsive to supprescin in a TATA-proximal region of a member of the phenylalanine ammonia-lyase gene family in pea were examined in vitro. Gel mobility-shift assays and DNase I footprinting analysis revealed that the promoter region of PSPAL2 was modified by the binding of nuclear factors at multiple sites that were possibly involved in supprescin-mediated deactivation. The prominent changes by supprescin were observed at boxes 2 and 4 and near exonic sequences.