Differential expression of genes encoding cell wall proteins in vascular tissues from vertical and bent loblolly pine trees

Differential expression of cell wall proteins during plant development and in response to biotic or abiotic stress suggests that these proteins may contribute in different ways to plant cell wall architecture. Because the wood of loblolly pine (Pinus taeda L.) is highly specialized in the formation of secondary cell walls, it is an ideal tissue for studying these proteins. The cDNAs coding for six novel cell wall associated proteins, as well as a homologue for a phytocyanin, were identified and characterized from differentiating xylem of loblolly pine. Three of these cDNAs encoded new putative loblolly pine arabinogalactan proteins, based on their structural similarity to classical arabinogalactan proteins (AGPs). In addition, one clone was related to the proline-rich protein group and the other two to the glycine-rich protein group and the mussel adhesive protein. Relative expression of these genes was examined in different tissues and organs from normal trees (needles, phloem and vertical wood), the underside of bent trees (compression wood) and the lateral sides of the bent stems (side wood). All clones, except one, were highly expressed in vascular tissues with noticeable differences among the three types of wood. Their relationships and diversity provide the first insights into concerted expression and related function for this important group of proteins in cell wall formation of wood.