Plant mitochondria have multiple energy-dissipating components in the respiratory chain. It is known that these components are induced under several stress conditions. Here we examined whether the gene expression pattern and its regulatory mechanism under high light (HL) conditions are different among the respiratory components in Arabidopsis leaves. Alternative oxidase (AOX) gene expression ( AOX1a and AOX1c ) and amount of protein were elevated after exposure to HL. In addition to AOX, the

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... ression of other respiratory genes, including NDA1 , NDB2 , NDC1 , UCP1 , UCP5 , COX6b and CI76 , was also induced by HL. NDB2 was co-expressed with AOX1a , but other HL-induced genes showed a distinct expression pattern. Manipulation of photosynthesis or respiration using several chemicals revealed that while the expression of AOX1a and NDB2 was mainly induced by inhibition of the respiratory chain, NDA1 expression was affected by photosynthesis-related reactive oxygen species. The expression of AOX1c , NDC1 , COX6b and CI76 was not induced by these manipulations. When plants were exposed to HL under a high CO 2 environment, the expression of several respiratory genes was more strongly induced, suggesting that modulations of cellular carbon status by elevated photosynthesis are involved in respiratory gene expression. Based on these results, we propose a mechanistic model of respiratory gene expression in illuminated leaves.