A cDNA MICROARRAY ANALYSIS OF DIFFERENTIAL GENE EXPRESSION DURING JUVENILE AND MATURE WOOD FORMATION IN PINE

¹ 1. Forest Biotechnology Group, Department of Forestry, North Carolina State University, Raleigh, NC 27695-8008 USA

² 2. Carnegie Institution of Washington, Department of Plant Biology, 260 Panama Street, Stanford, CA 94305 USA

³ 3. Institute of Forest Genetics, USDA Forest Service, Department of Environmental Horticulture, University of California, Davis, Davis, CA 95616 USA

Microarray techniques are increasingly utilized in functional genomic research for gene discovery, mapping and expression profiling. We have established cDNA microarrays from pine for large-scale screening to study differential gene expression in juvenile and mature wood development and to compare these changes to known stress responses. Juvenile wood has higher lignin, hemicellulose and moisture content, lower specific gravity, shorter tracheid length and greater microfibril angle. These characteristics account for major proportions of wood variation and affect the quality of timber, processed pulp, and paper products. We used a robotic system to construct microarrays consisting of 3107 elements within a 1.8 cm x 1.8 cm area. Among these elements 1152 were loblolly pine cDNAs from subtracted libraries of juvenile and mature developing xylem, 1935 were cDNAs from two ongoing pine EST projects, and 20 were serial dilutions of a GFP clone. These GFP clones were used to normalize the signal intensity before analysis. Probes were prepared from developing xylem at different developmental stages and after various stress treatments. Juvenile and mature developmental stage tissue was collected from the crown and base of 21-year-old trees. Water stress and heat stress were applied to two-year-old seedlings before harvesting xylem. Mechanical stress was applied to 6-year-old trees by bending for 6 days. Arrays were hybridized with probes combined in pairs for each treatment or developmental stage. Our preliminary results show large number of genes in xylem are differentially expressed between juvenile and mature stages, and also in response to water, heat, and mechanical stress.