Abstract
In order to understand carbohydrate metabolism regulated by sugar, we screened genes whose expression was regulated by sucrose using cDNA macro-arrays of Arabidopsis. In this study, we focused genes encoding putative beta-galactosidase, beta-xylosidase and beta-glucosidase induced by sugar starvation and designated them as GAL, XYL and GLU, respectively. They have glycosyl hydrolase domains and signal peptides. GAL showed high homology with a beta-galactosidase induced during fruit ripening of pear. Thus, we hypothesized that those proteins secrete and release monosaccharides from cell wall polysaccharides. In fact, the activity of glycosyl hydrolases in culture medium increased when sucrose was omitted from culture medium. Use of GUS reporter gene indicated activation of GAL promoter by dark treatment. In addition, cell wall polysaccharides such as hemicellulose and pectin decreased in sugar-starved leaves. Thus, it was indicated that cell wall polysaccharides are degraded to supply carbon source associating with sugar starvation.
