Gene Expression Profiling of the Tetrapyrrole Metabolic Pathway in Arabidopsis with a Mini-Array System 

Tetrapyrrole compounds, such as chlorophylls, hemes, and phycobilins, are synthesized in many enzymatic steps. For regulation of the tetrapyrrole metabolic pathway, it is generally considered that several specific isoforms catalyzing particular enzymatic steps control the flow of tetrapyrrole intermediates by differential regulation of gene expression depending on environmental and developmental factors. However, the coordination of such regulatory steps and orchestration of the overall tetrapyrrole metabolic pathway are still poorly understood. In this study, we developed an original mini-array system, which enables the expression profiling of each gene involved in tetrapyrrole biosynthesis simultaneously with high sensitivity. With this system, we performed a transcriptome analysis of Arabidopsis seedlings in terms of the onset of greening, endogenous rhythm, and developmental control. Data presented here clearly showed that based on their expression profiles at the onset of greening, genes involved in tetrapyrrole biosynthesis can be classified into four categories, in which genes are coordinately regulated to control the biosynthesis. Moreover, genes in the same group were similarly controlled in an endogenous rhythmic manner but also by a developmental program. The physiological significance of these gene clusters is discussed.