Metabolic regulation of genes encoding cytochrome c and cytochrome c oxidase subunit Vb in Arabidopsis
In this study an analysis of the expression of four Arabidopsis nuclear genes encoding components of the mitochondrial cyanide-sensitive respiratory pathway: two genes encoding cytochrome c oxidase subunit Vb (COX5b) and two genes encoding cytochrome c (Cytc), was carried out. Northern blot analysis indicated that these genes are expressed in several organs. Incubation of plants in solutions containing metabolizable sugars produced an increase in transcript levels. The effect of carbohydrates showed the same time and concentration dependence for the four genes, suggesting the operation of a common regulatory mechanism. Light produced an increase in transcript levels, although smaller than that produced by sugars. Incubation of plants in solutions with different nitrogen sources also produced changes in expression. In the presence of ammonium, higher transcript levels were observed with respect to plants treated with either nitrogen-free or nitrate solutions. Nitrate, on the other hand, produced a slight decrease in transcript levels and abolished the inducing effect of ammonium. Reporter enzyme activity in transgenic plants carrying a fusion of a Cytc gene promoter with the beta-glucuronidase coding region was increased by the inclusion of sucrose and ammonium in the culture medium. The present results suggest that carbon and nitrogen metabolites act in concert to regulate the expression of different components of the cyanide-sensitive respiratory pathway.