Abstract:
Tension wood has distinct physical and chemical properties, including altered fibre properties,
cell wall composition and ultrastructure. It serves as a good system for investigating the
genetic regulation of secondary cell wall biosynthesis and wood formation. The reference
genome sequence for Eucalyptus grandis allows investigation of the global transcriptional
reprogramming that accompanies tension wood formation in this global wood fibre crop.
We report the first comprehensive analysis of physicochemical wood property changes in
tension wood of Eucalyptus measured in a hybrid (E. grandis 9 Eucalyptus urophylla) clone,
as well as genome-wide gene expression changes in xylem tissues 3wk post-induction using
RNA sequencing.
We found that Eucalyptus tension wood in field-grown trees is characterized by an increase
in cellulose, a reduction in lignin, xylose and mannose, and a marked increase in galactose.
Gene expression profiling in tension wood-forming tissue showed corresponding down-regulation
of monolignol biosynthetic genes, and differential expression of several carbohydrate
active enzymes.
We conclude that alterations of cell wall traits induced by tension wood formation in
Eucalyptus are a consequence of a combination of down-regulation of lignin biosynthesis and
hemicellulose remodelling, rather than the often proposed up-regulation of the cellulose biosynthetic
pathway.
