The cystathionine-γ-synthase gene involved in methionine biosynthesis is highly expressed and auxin-repressed during wild strawberry (Fragaria vesca L.) fruit ripening

Differential screening of a cDNA library from ripe wild-strawberry (Fragaria vesca) receptacles allowed the isolation of a cDNA clone for an mRNA which accumulated to high levels in ripe strawberry receptacles. Sequence analysis of this cDNA (1940 bp) and the corresponding gene (4330 bp) indicated the presence of an ORF coding for a predicted protein of 545 amino acids (MWt 58.3 kDa) showing 91% identity with an Arabidopsis thaliana cystathionine γ-synthase (CGS), an enzyme involved in methionine biosynthesis. Up to now, CGS activity was reported only in leaves from various plants and in microorganisms. In this study, a much stronger expression was observed in receptacles from strawberries compared to other organs (leaves, flowers, etc.). Accumulation of CGS transcripts in receptacles of both wild and commercial strawberries was highly correlated with the progress of ripening. Immunoblot experiments with an A. thaliana CGS antibody demonstrated a similar profile of accumulation for CGS protein and transcripts. Southern-blot analysis of genomic DNA indicated that the CGS protein was encoded by a single gene in Fragaria species and in some climacteric fruits, e.g. peach and apricot. In addition to the ripening-related genes identified in strawberries, the treatment of receptacles (des-achenated or not) with the auxin NAA significantly reduced CGS gene expression.