Global transcription profiling reveals carbon and nitrogen interaction, sugar status and stress response, and the differential regulation of glucose induction versus glucose repression in model plant Arabidopsis thaliana
The Ohio State University
(October 30, 2003 11:30 AM - 12:30 PM)
Complex and interconnected signaling networks allow cells to integrate information that regulates growth, differentiation, cell division or programmed cell death. Plants can sense levels of nutrients such as carbon and nitrogen and accordingly adjust gene expression, which in turn affects metabolic and cellular activities. Numerous physiological studies have demonstrated that the availability and ratio of carbon and nitrogen are key determinants for plant growth and development. While this nutrient response is critical, our understanding of the molecular mechanisms underlying sugar or nitrogen signal transduction in plants is obscure. To begin unraveling complex sugar signaling networks in plants, DNA microarray analysis was used to determine the effects of glucose and nitrate on gene expression on a global scale in model plant Arabidopsis. Under the conditions used, glucose is a much more potent signal in regulating transcription than inorganic nitrogen, and that other than genes associated with nitrate assimilation, glucose had a greater effect in regulating nitrogen metabolic genes than nitrogen itself. Glucose also regulated a broader range of genes, including genes associated with carbohydrate metabolism, transcriptional regulation, and metabolite transport. Cluster analysis revealed significant interaction between glucose and nitrogen in regulating gene expression, because a combination of glucose and nitrogen could modulate the expression of many genes responsive either to glucose or nitrogen individually. A large number of genes associated with stress response were induced by glucose-we postulate that glucose signaling regulates these genes either via crosstalk with stress hormone ABA or ethylene signaling or via independent signal transduction mechanisms. Using cycloheximide, an inhibitor of protein synthesis, we have found that glucose repression appears to be a primary response while glucose induction is largely a secondary response requiring de novo protein synthesis. We conclude that glucose and inorganic nitrogen have dual roles in plants, acting as both metabolites and effective signaling molecules. Our long-term goal is to reveal the transcriptional cascades underlying sugar regulated gene expression in plants.