DIFFERENTIAL EXPRESSION OF THE S-ADENOSYL-L-METHIONINE SYNTHASE GENESDURING PEA DEVELOPMENT

Two genes coding for S-adenosyl-L-methionine synthase (SAMS, EC 2.5.1. 6) were previously isolated from pea (Pisum sativum) ovaries. Both SAM S genes were highly homologous throughout their coding regions but sho wed a certain degree of sequence divergence within the 5' and the 3' u ntranslated regions. These regions have been used as gene-specific pro bes to analyze the differential expression of SAMS1 and SAMS2 genes in pea plants. The ribonuclease protection assay revealed different expr ession patterns for each individual gene. SAMS1 was strongly expressed in nearly all tissues, especially in roots. SAMS2 expression was weak er, reaching its highest level at the apex. Following pollination, SAM S1 was specifically up-regulated, whereas SAMS2 was expressed constitu tively. The up-regulation of SAMS1 during ovary development was also o bserved in unpollinated ovaries treated with auxins. In unpollinated o varies an increase in SAMS1 expression was observed as a consequence o f ethylene production associated with the emasculation process. In sen escing ovaries both SAMS1 and SAMS2 genes showed increased expression. Ethylene treatment of unpollinated ovaries led to an increase in the SAMS1 mRNA level. However, SAMS2 expression remained unchangeable afte r ethylene treatment, indicating that SAMS2 induction during ovary sen escence was not ethylene dependent. SAMS mRNAs were localized by in si tu hybridization at the endocarp of developing fruits and in the ovule s of senescing ovaries. Our results indicate that the transcriptional regulation of SAMS genes is developmentally controlled in a specific w ay for each gene.