Isolation and functional analysis of sulfite oxidase gene AtSO promoter from Arabidopsis thaliana.

Sulfite oxidase (SO), one of the known molybdenum co-factor-containing enzymes, plays important roles in diverse metabolic processes such as sulfur detoxification and purine catabolism in mammals. But much less is known about the expression and regulatory characterization of sulfite oxidase gene in higher plants. In this report, expression of Arabidopsis SO is characterized in detail by semi-quantitative RT-PCR and histochemical staining. The results showed that the transcripts of AtSO were predominantly detected in Arabidopsis aerial tissues including stems, young leaves, young inflorescences and immature siliques at higher level, but in roots with a lower level. To monitor AtSO expression in plant, the promoter region containing a 1 562-bp genomic sequence from AtSO was isolated and analyzed using methods of bioinformatics. Basing on the distribution of beta-glucuronidase (GUS) activities shown by histochemical staining in transgenic Arabidopsis plants harboring the promoter-uidA fusion construct, it can be concluded that AtSO is expressed mainly in the green tissues/organs in a light-dependent way. In addition, its expression is up-regulated during sulfite treatment. The information from this study may provide useful clue for further functional analysis of plant SO homologs during light-induced development of leaf tissue and/or excessive sulfite/SO(2) gas stresses in higher plants.