| Research Abstract |
A chimeric promoter in which the sulfur responsive element (βSR) from the βsumunit promoter of β-conglycinin was inserted at the -90 position of the CaMV 35S promoter showed sulfur deficiency response in rosette leaves. A transgenic Arabidopsis line, termed NOB, which carries GFP gene under the control of this promoter was constructed. Effects of various chemicals, including O-acetylserine (OAS), were analyzed using the NOB plants. The results indicated that the βSR element plays important roles in the sulfur deficiency response, Treatment of the NOB plants with cytokinin enhanced the GFP fluorescence as well as expression of the endogenous sulfur deficiency-responsive genes. We isolated mutants that show elevated levels of GFP fluorescence by using the NOB plant as a parental line. In osh1 mutant, an epigenetic change was found in a thiol reductase gene, and levels of OAS and endogenous sulfur deficiency-responsive genes were upregulated. In another mutant, nbm2, the level of OAS was reduced but expression of endogenous sulfur deficiency-responsive genes was upregulated. This mutant was found to bear a mutation in a gene that is involved in auxin response. Expression of the β subunit gene is down-regulated by methionine treatment. Introduction of mto1 mutation, which shows elevated level of soluble methionine, down-regulated GFP fluorescence in seeds but not in rosette leaves. On the other hand, a chimeric promoter consisted of the β subunit gene promoter and the enhancer region of CaMV 35S promoter responded to methionine in rosette leaves. The results depicts a tissue-specific response of the β subunit gene promoter.
|
