Abstract
Hydrogen peroxide (H(2)O(2)) is discussed as being a signaling molecule in Arabidopsis (Arabidopsis thaliana) leaf senescence. Intracellular H(2)O(2) levels are controlled by the H(2)O(2)-scavenging enzyme catalase in concert with other scavenging and producing systems. Catalases are encoded by a small gene family, and the expression of all three Arabidopsis catalase genes is regulated in a senescence-associated manner. CATALASE2 (CAT2) expression is down-regulated during bolting time at the onset of leaf senescence and appears to be involved in the elevation of the H(2)O(2) level at this time point. To understand the role of CAT2 in senescence regulation in more detail, we used CAT2 promoter fragments in a yeast one-hybrid screen to isolate upstream regulatory factors. Among others, we could identify G-Box Binding Factor1 (GBF1) as a DNA-binding protein of the CAT2 promoter. Transient overexpression of GBF1 together with a CAT2:beta-glucuronidase construct in tobacco (Nicotiana benthamiana) plants and Arabidopsis protoplasts revealed a negative effect of GBF1 on CAT2 expression. In gbf1 mutant plants, the CAT2 decrease in expression and activity at bolting time and the increase in H(2)O(2) could no longer be observed. Consequently, the onset of leaf senescence and the expression of senescence-associated genes were delayed in gbf1 plants, clearly indicating a regulatory function of GBF1 in leaf senescence, most likely via regulation of the intracellular H(2)O(2) content.