PARENT SESSION
Contributed Oral Session 154: Photosynthesis and Water Relations: Climate Effects
Friday, August 12, 8:00 AM - 11:30 AM, Meeting Room 515 A, Level 5, Palais des congrès de Montréal

Gene expression patterns of loblolly pine exposed to elevated CO₂ in the field.

Moura, Catarina^*,1, Grene, Ruth², Jackson, Robert¹, ¹ Duke University, Durham, NC² Virginia Tech, Blacksburg, VA

ABSTRACT- Atmospheric CO₂ concentration has been rising since the Industrial Revolution and is expected to double during the next century, thus altering the environment for current forest species. Acclimation of trees to a new environment requires molecular responses that include changes in the expression of a large number of genes controlling important physiological and ecological processes. Large-scale analysis of gene expression is now possible through the use of novel approaches such as microarray technology. Microarrays allow the comparison of expression profiles of hundreds or thousands of genes simultaneously and can therefore help to identify molecular networks and regulatory mechanisms involved in tree response to environmental change. We used cDNA microarrays to compare gene expression patterns of loblolly pine trees growing in the field under ambient and elevated (ambient + 200mol mol^-1) CO₂ concentrations. RNA extracted from pine needles sampled over a growing season was hybridized to microarrays containing 1790 replicated cDNAs assigned to a range of functional categories. There were strong seasonal effects on the total number of genes differentially expressed between ambient and elevated CO2 (a minimum of 35 in March to a maximum of 853 in August). Among these, more genes were upregulated under elevated CO2 than downregulated, except in July (177 up vs. 183 down). Genes coding for enzymes involved in carbon metabolism, such as citrate synthase and glucose-6-phosphate isomerase, were upregulated in elevated CO₂ during most of the growing season. The same pattern was observed for an alanine-aminotransferase gene involved in both carbon and aminoacids metabolism. Genes coding for the enzyme rubisco showed no differential expression between ambient and elevated CO₂. This result suggests that either photosynthetic downregulation was not present or that it occurred through an alternative mechanism with no repression of rubisco genes. This application of genomic-scale analysis to field experiments is an important step towards a more mechanistic understanding of tree response to global climate change.

Key words: Gene expression, Microarrays, Elevated CO₂, Loblolly pine