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 pycnospor e germination fluid of a pea pathogen Mycospharella pinodes. A nuclear run-on assay revealed that supprescin rapidly deactivated elicitor-tr iggered 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 p athogen was investigated. Cis-acting sequences and trans-acting factor s responsive to supprescin in a TATA-proximal region of a member of th e phenylalanine ammonia-lyase gene family in pea were examined in vitr o. Gel mobility-shift assays and DNase I footprinting analysis reveale d that the promoter region of PSPAL2 was modified by the binding of nu clear factors at multiple sites that were possibly involved in suppres cin-mediated deactivation. The prominent changes by supprescin were ob served at boxes 2 and 4 and near exonic sequences.