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International audience; Reaction wood originates from cambial activity which will adjust cell division activity, cell wall structure and properties, so that the resulting growth event will be the appropriate response to endogenous and environmental stimuli. When addressing the question of the induction of reaction woodformation, the physical parameters inducing reaction wood are first presented leading to discuss the importance of gravisensing versus proprioception (sensing of the local curvature of the stem) in this process. Molecular candidates for the perception of cellular deformation that ishypothesized to occur in a gravistimulated stem are located at CPMCW (cytoskeleton-plasma membrane-cell wall) continuum. These candidates would mediate intracellular signalling. Insights from global approaches (e.g. transcriptome and proteome analyses) performed on tilted trees suggest calcium, reactive oxygen species and phosphatidy linositol signalling in the gravitropism sensing network. It has been unambiguously shown that several of the aux/IAA gene family mediators of auxin signal transduction pathway change on induction of tension wood formation. Gibberellins and ethylene seem also to be involved in reaction wood formation.The role of the different plant hormones in upstream primary response to reaction wood sensing or alternatively in the transmission of the signal from the perception to the reaction wood forming cells is discussed. more...

MECA; The wall-associated kinases (WAKs) are a family of transmembrane proteins involved in pathogen responses and cell elongation in Arabidopsis. They belong to the major receptor-like kinase (RLK) family in plants. Given their architecture and connection to the cell wall, WAKs are thought to perceive and propagate extracellular signals. This study reports the characterization of the WAK family in a woody species based on the v3.0 genome assembly of Populus trichocarpa. In silico analysis revealed a total of 175 PtWAK sequences classified into four groups based on protein domains. Of the PtWAKs, 91.5 % were found in tandem-duplicated clusters contributing to the expansion of the family in poplar. Microarray and EST expression data mining revealed contrasting temporal and spatial expression patterns in stress treatments for several WAK members. The WAKs in poplar form the largest WAK family encountered to date in plants. The combination of phylogenetic and transcriptional data showed that members in nonexpanded clusters were mainly expressed in developmental processes, whereas PtWAKs that had evolved independently in a species-specific way were structured in clusters and were involved in resistance responses. This paper offers an overview of WAK family structure in P. trichocarpa, which will be useful for further functional analysis of the PtWAK family. more...

The book is an essential reference source on reaction wood for wood scientists and technologists, plant biologists, silviculturists, forest ecologists, and anyone involved in the growing of trees and the processing of wood. It brings together our current understanding of all aspects of reaction wood, and is the first book to compare and discuss both compression wood and tension wood. Trees produce reaction wood to maintain the vertical orientation of their stems and the optimum angle of each branch. They achieve this by laying down fibre cell walls in which differences in physical and chemical structure from those of normal fibres are expressed as differential stresses across the stem or branch. This process, while of obvious value for the survival of the tree, causes serious problems for the utilisation of timber. Timber derived from trees containing significant amounts of reaction wood is subject to dimensional instability on drying, causing distortion and splitting. It is also difficult to work as timber, and for the pulp and paper industry the cost of removing the increased amount of lignin in compression wood is substantial. This has both practical and economic consequences for industry. Understanding the factors controlling reaction wood formation and its effect on wood structure is therefore fundamental to our understanding of the adaptation of trees to their environment and to the sustainable use of wood. more...