TISSUE-SPECIFIC EXPRESSION CONFERRED BY THE S-ADENOSYL-L-METHIONINE SYNTHETASE PROMOTER OF ARABIDOPSIS-THALIANA IN TRANSGENIC POPLAR

In Arabidopsis the promoter of the gene encoding S-adenosyl-L-methioni ne synthetase (SAM-S) Psam-1 confers: expression preferentially in the vascular tissue. In search for promoters that drive expression in par ticular cells of the lignifying tissues in trees, we have analyzed the expression pattern conferred by the Psam-1 promoter in transgenic pop lar. Histochemical analyses demonstrated beta-glucuronidase (GUS) acti vity mainly in phloem and cortex tissue throughout the plant, and in r oot tips. Fluorimetric assays showed high GUS activity in the tissues outside (phloem, cortex and cork) compared to those inside (xylem and pith) of the cambial layer. In contrast, the endogenous SAM-S activity was high in tissues inside and low in tissues outside of the cambial layer. RNA gel blot analysis demonstrated a high transcript level of t he endogenous sam-s gene(s) in tissues both outside and inside the cam bial layer. This indicates that the low SAM-S activity in the bark was at least partially due to translational and/or post-translational reg ulation of the endogenous sam-s gene(s). In dormant transgenics, the t issue specificity was conserved, but the activity levels were up to 10 -fold reduced.