Digging in wood
Résumé
Wood, which represents the most abundant lignocellulosic biomass on earth, fulfils key roles in trees, and is also a raw material for multiple end-uses by mankind. The differentiation of this complex vascular tissue starts with cell division in the vascular cambium and is characterized by a massive deposition of lignified secondary cell walls mainly in fibres and vessels. A transcriptional network underlying this differentiation process ensures a tight regulation of the expression of thousands of genes both at the spatial and temporal levels. Most of our current knowledge of this hierarchical network was extrapolated from studies performed in Arabidopsis. Here, we review recent findings on the regulation of wood formation in angiosperm trees species highlighting conserved and distinct mechanisms with Arabidopsis. We provide examples shedding light on the central role of auxin and its cross-talk with other hormones at different stages of secondary xylem differentiation. Functional studies of trees' wood-associated transcription factors revealed diversified functions as compared to their Arabidopsis orthologs. Sophisticated mechanisms of alternative splicing and cross-regulation between the two distinct groups of top level NAC-domain master regulators were uncovered. These findings underlie the high level of complexity of wood formation in trees and provide a framework for future lines of research in this exiting research field.