Transcriptome profiling of wood maturation in Pinus radiata identifies differentially expressed genes with implications in juvenile and mature wood variation

Trees usually produce wood with distinct properties at different developmental stages. Juvenile wood (JW) formed in younger trees has poorer properties than mature wood (MW) formed in later years. We used cDNA microarrays to compare the xylem transcriptomes of Pinus radiata trees synthesising JW and MW respectively. JW and MW formation involved considerable transcriptome flux, with the greatest change occurring in spring (19.3%) compared to autumn (9.2%). We identified 147 candidate genes in response to wood maturation, of which 34.0% were implicated in cell wall formation and 19.7% were functional unknowns. Majority of the candidate genes were identified from MW and JW in spring (127) with fewer genes in autumn (30). Many genes involved in secondary wall formation (cellulose synthesis and lignification) and cytoskeleton development were more transcribed in MW in spring, while in JW in spring most genes functioned in primary wall synthesis, signalling and stress responses. Some identified genes may play roles in sensing environmental signals during the transition from JW to MW and in controlling distinct tracheids and wood traits between JW and MW.