FUNCTIONAL-ANALYSIS OF THE PROMOTERS OF PHENYLALANINE AMMONIA-LYASE GENES IN PEA

Pycnospore germination fluid of Mycosphaerella pinodes, a fungus patho genic on pea, contains both an elicitor and a suppressor of the accumu lation of pisatin, a major phytoalexin of pea. Transcription of the ge nes encoding key enzymes in the biosynthesis of pisatin, namely PAL (a gene encoding phenylalanine ammonia-lyase) and CHS (a gene encoding c halcone synthase), was shown to be activated upon the treatment of pea epicotyl tissues with the fungal elicitor and suppressed upon treatme nt with the fungal suppressor. To investigate the mechanisms underlyin g activation and suppression of plant defense genes by signal molecule s secreted by a fungal pathogen and other stresses, such as ultraviole t (UV) light, we constructed chimeric genes composed of the 5'-flankin g regions of two members of the PSPAL family (the genes encoding pheny lalanine ammonia-lyase in Pisum sativum) fused to a bacterial gene for chloramphenicol acetyltransferase. Then, the cis-regulatory elements necessary for elicitor-mediated activation and suppresser-mediated sup pression were examined in pea protoplasts. Functional analysis of 5' n ested deletions of PSPAL1 and PSPAL2 suggested that an enhancer-like e lement is located in the TATA-distal region (-2,196 to -406) in PSPAL2 . A cis-acting element(s) responsible for elicitor-mediated activation was found in the TATA-proximal region (-340 to -95 in PSPAL1; -406 to -158 in PSPAL2), in which the consensus sequence motifs known as box 1, box 2 and box 4 [Yamada et al. (1992) Plant Cell Physiol. 33: 715, Lois et al. (1989) EMBO J. 8: 1641] were present in close proximity. F urthermore, both promoters were activated by UV light but were partial ly suppressed in response to the fungal suppressor.