Regulation of glutamate-1-semialdehyde aminotransferase expression during tomato (Lycopersicon esculentum Mill.) fruit development

A full-length clone that encodes tomato fruit tissue (Lycopersicon esculent um Mill. 'Rutgers') glutamate-1-semialdehyde aminotransferase (GSAT; EC 5.4 .3.8) was isolated and characterized. Amino acid sequence analysis showed t hat the tomato GSAT clone exhibited a high level of homology to the amino a cid sequences of corresponding GSAT proteins from other plant species. The primary structure of GSAT consists of a 481-amino acid precursor that inclu des a 46.7 kilounit (kU), 437-amino acid mature protein and a transit pepti de of 44 amino acids. Southern analysis showed that a single copy of the GS AT gene was present in the tomato genome. Northern analysis showed that the abundance of GSAT transcripts declined throughout tomato fruit development and ripening. GSAT protein content decreased dramatically by 25 days posta nthesis, and GSAT protein was undetectable by day 45, the approximate begin ning of chlorophyll loss and carotenoid synthesis. These results show that GSAT is regulated developmentally at the level of transcript accumulation. In addition, posttranscriptional regulation may occur through decreased tra nslation or increased degradation of GSAT protein.