PARENT SESSION
Posters P6B Photosynthetic acclimation: Mechanisms and gene expression. Abstracts (531-578)

Gene expression during light adaptation in Arabidopsis thaliana. Elke Rosche^*,1, Susanne von Caemmerer¹, Murray Badger¹, ¹ Molecular Plant Physiology Group, Australia

ABSTRACT- Many plants, including Arabidopsis, are able to adapt to elevated light environments by changing the biochemical and physiological properties of their leaves and chloroplasts. Long term acclimation leads to changes in leaf morphology and photosynthetic capacity, while short term adaptation includes the expression of genes and proteins involved in aspects of photoprotection. However, signalling pathways from light perception to gene and protein expression and the time frame of expression leading to the long-term acclimation are poorly understood. We are interested in the global changes of gene expression during adaptation to high light conditions. Here we used the ATH1 GeneChip (Affymetrix) to document changes in gene expression during a time course experiment of illumination with high light. We document the changes in gene expression in shade grown plants during exposure to elevated light for up to 6 hours and the subsequent physiological acclimation over 10 days. We compare the onset of transcription for photosynthetic and non-photosynthetic genes with the increase in electron transport and CO2 fixation. Photosynthesis in shade-adapted plants began to increase after one day of high light irradiation and continued to rise significantly for about 5 days. The CO2 fixation rate in high light grown plants was about twice as high as the rate achieved by shade grown leaves after 10 days of light exposure, which is consistent with the different leaf morphology of these plants. The increase in CO2 fixation was accompanied by increasing levels of total chlorophyll and protein. At the transcriptional level genes involved in photosynthesis and protection of the photosynthetic apparatus were either already highly expressed in shade or induced shortly after exposure to high light. Genes involved in the degradation of fatty acids and starch were upregulated shortly after light exposure and continued to increase during the first 6 hours of light exposure. Several transcription factors and heat shock proteins were transiently induced during the first half hour of high light treatment. Hormone-responsive genes and other signalling proteins and transcription factors changed their expression within 2-6 hours of light exposure.

KEY WORDS: gene expression, light acclimation, photosynthesis, signalling