Relationship between development of compression wood and gene expression

In gymnosperms, tissue that differs from normal wood develops on the lower side of an inclined stem or branch and is referred to as compression wood. Compression wood is characterized by thicker tracheid walls, higher lignin content, and shorter tracheid length, among other features. No definable boundary exists between normal wood and compression wood, and compression wood is classified continuously from mild to severe. Therefore, kinds and abundances of transcripts are expected to be considerably different between mild and severe compression wood. We prepared Chamaecyparis obtusa saplings grown at various angles of inclination (0-50°) to obtain normal, mild, and severe compression wood samples. We examined the relationship between the degree of development of compression wood and relative transcript abundance of previously screened genes. Lignin content and relative abundance of a transcript with high similarity to laccase increased with increasing inclination angle of the saplings, i.e. development of compression wood. In contrast, tracheid length decreased with increasing development of compression wood, and in samples where the tracheid length was short, relative abundance of a transcript with high similarity to ascorbate oxidase decreased.