Temporal and spatial pattern of expression of the pea phenylalanine ammonia-lyase gene1 promoter in transgenic tobacco

Genes encoding phenylalanine ammonia-lyase (PAL) form a small multigene family with at least three members in pea. Tissue-specific expression of the promoter of a member of PAL gene family (PSPAL1) was investigated in the transgenic tobacco transformants carrying the different modes of chimeric fusion between the PSPAL1 promoter and a bacterial β-glucuronidase (GUS) gene. In stems, at least, strict correlation was found between steady-state levels of Gus-mRNA and enzyme activity. Significantly high level of GUS activity was observed in roots, particularly in meristematic tissues and the pigmented region of petals of transgenic tobacco carrying the translational fusion type B (-1,394 to +140 of PSPAL1 connected to Gus), followed by moderately high level of GUS activity carrying the translational fusion type A (-1,394 to + 117). GUS expression in tissues of mature leaves, however, was very low in these constructs. Extremely low GUS activity was observed in the transformants of transcriptional fusion type (-1,394 to +5), whilst no activity was detected carrying non-transcription fusion type (-1,394 to -27). Furthermore, the pattern of the PSPAL1 expression was characterized in response to pathogen ingress and woundings in transgenic tobacco carrying the translational fusion type B. Woundings itself triggered marked expression of PSPAL1 driven GUS expression at the wounded sites. Inoculation of nonpathogens, Phytophthora capsici, P. boehmeriae and Erisiphe graminis f. sp. hordei, both caused rapid and very clear GUS expression zone along with the development of hypersensitive cell death area where callose was accumulated, however, the inoculation of a pathogen, P. nicotiana caused slow and hazy GUS expression zone along with the lesion development. These results suggest that the expression of pea PSPAL1 promoter is regulated in a similar fashion, at least in a part, in pea and transgenic tobacco, under the plant development and various environmental cues.