Wood formation is a complex developmental process governed by genetic and environmental
stimuli. Populus and Eucalyptus are fast-growing, high-yielding tree genera that represent
ecologically and economically important species suitable for generating significant
Comparative analysis of the developing xylem and leaf transcriptomes of Populus
trichocarpa and Eucalyptus grandis together with phylogenetic analyses identified clusters of
homologous genes preferentially expressed during xylem formation in both species.
A conserved set of 336 single gene pairs showed highly similar xylem preferential expression
patterns, as well as evidence of high functional constraint. Individual members of multigene
orthologous clusters known to be involved in secondary cell wall biosynthesis also
showed conserved xylem expression profiles. However, species-specific expression as well as
opposite (xylem versus leaf) expression patterns observed for a subset of genes suggest subtle
differences in the transcriptional regulation important for xylem development in each species.
Using sequence similarity and gene expression status, we identified functional homologs
likely to be involved in xylem developmental and biosynthetic processes in Populus and
Eucalyptus. Our study suggests that, while genes involved in secondary cell wall biosynthesis
show high levels of gene expression conservation, differential regulation of some xylem development
genes may give rise to unique xylem properties.