title: Biosynthesis of cellulose-enriched tension wood in Populus: global analysis of transcripts and metabolites identifies biochemical and developmental regulators in secondary wall biosynthesis.
abstract: Stems and branches of angiosperm trees form tension wood (TW) when exposed to a gravitational stimulus. One of the main characteristics of TW, which distinguishes it from normal wood, is the formation of fibers with a thick inner gelatinous cell wall layer mainly composed of crystalline cellulose. Hence TW is enriched in cellulose, and deficient in lignin and hemicelluloses. An expressed sequence tag library made from TW-forming tissues in Populus tremula (L.) x tremuloides (Michx.) and data from transcript profiling using microarray and metabolite analysis were obtained during TW formation in Populus tremula (L.) in two growing seasons. The data were examined with the aim of identifying the genes responsible for the change in carbon (C) flow into various cell wall components, and the mechanisms important for the formation of the gelatinous cell wall layer (G-layer). A specific effort was made to identify carbohydrate-active enzymes with a putative function in cell wall biosynthesis. An increased C flux to cellulose was suggested by a higher abundance of sucrose synthase transcripts. However, genes related to the cellulose biosynthetic machinery were not generally affected, although the expression of secondary wall-specific CesA genes was modified in both directions. Other pathways for which the data suggested increased activity included lipid and glucosamine biosynthesis and the pectin degradation machinery. In addition, transcripts encoding fasciclin-like arabinogalactan proteins were particularly increased and found to lack true Arabidopsis orthologs. Major pathways for which the transcriptome and metabolome analysis suggested decreased activity were the pathway for C flux through guanosine 5'-diphosphate (GDP) sugars to mannans, the pentose phosphate pathway, lignin biosynthesis, and biosynthesis of cell wall matrix carbohydrates. Several differentially expressed auxin- and ethylene-related genes and transcription factors were also identified.
authors.affiliation: Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, 901 83 Umeå, Sweden.
authors.forename: Sara
authors.initials: S
authors.lastname: Andersson-Gunnerås
authors.forename: Ewa J
authors.initials: EJ
authors.lastname: Mellerowicz
authors.forename: Jonathan
authors.initials: J
authors.lastname: Love
authors.forename: Bo
authors.initials: B
authors.lastname: Segerman
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Ohmiya
authors.forename: Pedro M
authors.initials: PM
authors.lastname: Coutinho
authors.forename: Peter
authors.initials: P
authors.lastname: Nilsson
authors.forename: Bernard
authors.initials: B
authors.lastname: Henrissat
authors.forename: Thomas
authors.initials: T
authors.lastname: Moritz
authors.forename: Björn
authors.initials: B
authors.lastname: Sundberg
mesh_terms: D002473:Cell Wall / Q000378:metabolism*; D002482:Cellulose / Q000378:metabolism*; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D032107:Populus; D012333:RNA, Messenger / Q000235:genetics*; D014934:Wood
chemical_list: D012333:RNA, Messenger; D002482:Cellulose