In situ expression of trehalose synthesizing genes, TPS1 and TPPB, in Arabidopsis thaliana using the GUS reporter gene

Two transgenic Arabidopsis lines were derived that expressed promoter regions for either AtTPS1 (At1g78580) or AtTPPB (At1g78090) using constructs containing the β-glucuronidase (GUS) reporter gene. These two genes function in tandem to produce the disaccharide, trehalose, and they likely have important regulatory and signaling functions in higher plants. Both genes were expressed nearly constitutively in Arabidopsis and expression was high in younger tissue and typically diminished with age. Similar expression patterns for both promoters were observed in etiolated and in light grown seedlings. Dense expression of both genes was observed during germination on day 1 but expression was absent from hypocotyls 3 days later. In contrast to AtTPS1, the expression of AtTPPB was concentrated in the root meristem of 7-day old light grown seedlings. The expression of both AtTPS1 and AtTPPB was mainly observed in young, actively dividing tissues, such as the shoot apex, and in flower parts including anthers, pistils, siliques and developing seeds. Expression of both genes also was clearly associated with vascular bundles, the root-hypocotyl junction, the pedicel-silique junction and related structures involved in bulk solute transport. Transcript levels of AtTPS1 and AtTPPB were either repressed or were little affected by exogenous sucrose, glucose, fructose or trehalose when measured by quantitative real-time PCR. However, both trehalose biosynthesis genes were induced two to tenfold by sorbitol, mannitol and NaCl. Responses of AtTPS1 and AtTPPB to the same chemical and stress treatments were not detected by changes in GUS activity. This may be due to the stability of the GUS protein relative to transcript levels. Because AtTPS1 and AtTPPB function in tandem to produce trehalose it was not surprising that the expression of both genes was distributed similarly in Arabidopsis tissues.