Transcriptional regulation of secondary growth in Arabidopsis thaliana.

Despite its economic and environmental significance, understanding the molecular biology of secondary growth (i.e. wood formation) in tree species has been lagging behind that of primary growth, primarily due to the inherent difficulties of tree biology. In recent years, Arabidopsis has been shown to express all of the major components of secondary growth. Arabidopsis was induced to undergo secondary growth and the transcriptome profile changes were surveyed during secondary growth using 8.3 K Arabidopsis Genome Arrays. Twenty per cent of the approximately 8300 genes surveyed in this study were differentially regulated in the stems treated for wood formation. Genes of unknown function made up the largest category of the differentially expressed genes, followed by transcription regulation-related genes. Examination of the expression patterns of the genes involved in the sequential events of secondary growth (i.e. cell division, cell expansion, cell wall biosynthesis, lignification, and programmed cell death) identified several key candidate genes for the genetic regulation of secondary growth. In order to gain further insight into the transcriptional regulation of secondary growth, the expression patterns of the genes encoding transcription factors were documented in relation to secondary growth. A computational biology approach was used to identify regulatory cis-elements from the promoter regions of the genes that were up-regulated in wood-forming stems. The expression patterns of many previously unknown genes were established and various existing insights confirmed. The findings described in this report should add new information that can lead to a greater understanding of the secondary xylem formation process.