PARENT SESSION
Posters P2B Light, redox and metabolic regulation: Light Reactions. Abstracts (444-478)

Photosynthetic redox regulation of Arabidopsis nuclear genes. Mirva Piippo^*,1, Yagut Allahverdiyeva¹, Natalia Battchikova¹, Eva-Mari Aro¹, ¹ Department of Biology, Turku, Finland

ABSTRACT- Various environmental conditions like temperature, light or nutrient stress are sensed in chloroplasts as changes in the steady-state redox state of the photosynthetic electron transfer components and/or of the coupled redox active components in the stroma. These redox signals are thought to be conveyed to the nucleus in order to initiate the acclimation processes. Redox-mediated cross-talk between the chloroplasts and the nucleus has earlier been addressed particularly for the regulation of the lhcb genes. We have used Arabidopsis cDNA microarrays to get a more comprehensive view on the regulation of nuclear genes by chloroplast redox signals, particularly the redox state of the PQ-pool. The redox state in Arabidopsis chloroplasts was modulated by illuminating mature leaves with different quality and quantity of light, with growth light samples always serving as a control. Leaf samples were collected for gene expression analysis as well as for various biochemical and biophysical measurements. After three hours of illumination, the gene expression profiles of leaves treated in darkness, low light, or light that excites predominantly photosystem II (PSII-light), or photosystem I (PSI-light) were much more similar than those of the high light treated leaves, which most often had an opposite gene expression profile to the other treatments. The expression of many genes participating in the carbohydrate metabolism was significantly changed. Only a small proportion of the genes of all circa 6500 different genes in the array had opposite expression in PSII and PSI-light treated leaves with reduced and oxidized PQ-pool, respectively, suggesting that the redox state of the PQ-pool exerts a regulatory role only on a limited number of nuclear genes. The small number of putative PQ-regulated genes, of which only five had a chloroplast targeting signal, indicates a lesser role for PQ-pool in the regulation of nuclear gene expression than has been previously thought.

KEY WORDS: Plastoquinone pool, Gene expression