Wood Formation from the Base to the Crown in Pinus Radiata: Gradients of Tracheid Wall Thickness, Wood Density, Radial Growth Rate and Gene Expression

Abstract

Wood formation was investigated at five heights along the bole for two unrelated trees of Pinus radiata. Both trees showed clear gradients in wood properties from the base to the crown. Cambial cells at the base of the tree were dividing 3.3-fold slower than those at the crown, while the average thickness of cell walls in wood was highest at the base. Cell wall thickness showed an overall correlation coefficient of >0.7 with wood density in both genotypes. Microscopic examination of developing tracheids showed that 33% of cells had formed secondary cell walls at the base of the tree, reducing to 3% at the crown. In total, 455 genes differentially expressed in developing xylem tissue from either the base or the crown were identified using modified differential display. RT-PCR analysis of 156 genes confirmed differential expression for 77%. Of the genes tested, 73% showed gradients in transcript abundance either up or down the bole of the tree, although the steepness of the gradients differed between genes. Genes involved in cell division and expansion tended to be more highly expressed in the crown of the tree, and two putative cell-cycle repressor genes were expressed 2-fold higher at the base. Conversely, transcripts of genes involved in secondary wall thickening were more abundant at the base of the tree. These results suggest that differences in the rate of cambial cell division, differences in the rate and duration of tracheid wall thickening, and differences in gene expression underpin the gradients of wood properties found in pines.

Association Genetics of Wood Physical Traits in the Conifer White Spruce and Relationships With Gene Expression

“…The P. glauca a-tubulin gene (TUA2) is highly similar to sequences that have been linked to the formation of cortical microtubules in P. taeda (González-Martínez et al 2007), developing xylem-preferential transcript accumulation in P. radiata (Cato et al 2006), ESTs that are unique to xylem librairies in Populus (Pilate et al 2004), and transcripts levels that correlated with auxin concentration in developing secondary xylem in P. tremula x tremuloides (Nilsson et al 2008). A b-tubulin gene was shown to be preferentially expressed in xylem in Eucalyptus (Paux et al 2004).…”

Modelling variation in wood density within and among trees in stands of New Zealand-grown radiata pine

“…Previous research has suggested that the gradients of wood properties found in radiata pine are underpinned by differences in the rate of cambial cell division, differences in the rate and duration of tracheid wall thickening, and differences in gene expression (Cato et al 2006). In the radial direction, wood density increased rapidly with increasing ring number from the pith before reaching a quasiasymptotic value such that little change in density occurred after approximately ring 20.…”

Transcriptome analysis provides insights into wood formation during larch tree aging

“…Especially, using cryosectioning and RNA-Seq methods, Xu et al (2016) compared the transcriptome of vascular cambium tissue in Cunninghamia lanceolata at juvenile, transitional, and mature stages to study the effects of age on cambium activity. Within-tree transcriptome and proteome profiling in wood-forming tissues based on changes of cell size and other wood properties have also been studied (Cato et al 2006;Garces et al 2014;Kumar et al 2009;Lorenz and Dean 2002;Paiva et al 2008;Ranik et al 2006). However, the regulatory network of age effects on the processes of wood formation remains poorly understood, and systematic investigation at the genome level is still needed.…”