Nature http://doi.org/zjh (2014)

The secondary cell walls of xylem are composed of polysaccharide fibres embedded in a lignin matrix, providing mechanical support for the plant. The chemical composition of this hard shell depends on biosynthetic enzymes regulated by transcription factors. Siobhan Brady, of UC Davis, Samuel Hazen, of UMass Amherst, and colleagues have taken a systems biology approach to decipher the gene network controlling the biosynthesis of this major component of wood. Their analysis links its complex topology to plant responses to external perturbations.

The authors built a map of all protein–DNA interactions between the promoter sequences of the fifty most important xylem-specific genes and hundreds of transcription factors, based on individual assays in yeast. The network is dominated by highly redundant connections, ‘power edges’, between groups of transcription factors and promoters. Multiple feed-forward loops, both directly and indirectly affecting target genes, make for a robust transcriptional network structure. However, abiotic stresses modify specific sub-networks, allowing the plant to precisely adapt the properties of their cell walls to the environment.

This work again shows how a systems biology approach to signalling pathways can bypass the limitations of genetic screens, and so get closer to the true complexity of biological responses. It may also translate into more efficient biofuel crops through cell-wall engineering.