title: Cloning and expression analysis of a wood-associated xylosidase gene (PtaBXL1) in poplar tension wood.
abstract: In stems of woody angiosperms responding to mechanical stress, imposed for instance by tilting the stem or formation of a branch, tension wood (TW) forms above the affected part, while anatomically distinct opposite wood (OW) forms below it. In poplar TW the S3 layer of the secondary walls is substituted by a "gelatinous layer" that is almost entirely composed of cellulose and has much lower hemicellulose contents than unstressed wood. However, changes in xylan contents (the predominant hemicelluloses), their interactions with other wall components and the mechanisms involved in TW formation have been little studied. Therefore, in the study reported here we determined the structure and distribution of xylans, cloned the genes encoding the xylan remodeling enzymes beta-xylosidases (PtaBXLi), and examined their expression patterns during tension wood, normal wood and opposite wood xylogenesis in poplar. We confirm that poplar wood xylans are substituted solely by 4-O-methylglucuronic acid in both TW and OW. However, although glucuronoxylans are strongly represented in both primary and secondary layers of OW, no 4-O-methylGlcA xylan was found in G-layers of TW. Four full-length BXL cDNAs encoding putative beta-xylosidases were cloned. One, PtaBXL1, for which xylosidase activity was confirmed by heterologous expression in Escherichia coli, exhibited a wood-specific expression pattern in TW. In conclusion, xylan as PtaBXL1, encoding beta4-xylosidase activity, are down-regulated in TW.
authors.affiliation: Laboratoire de Chimie des Substances Naturelles, Groupe de Glycobiologie Forestière, Faculté des Sciences et Techniques, 123, Avenue Albert Thomas, 87060 Limoges, Cédex, France.
authors.forename: Raphael
authors.initials: R
authors.lastname: Decou
authors.forename: Sabine
authors.initials: S
authors.lastname: Lhernould
authors.forename: Françoise
authors.initials: F
authors.lastname: Laurans
authors.forename: Elodie
authors.initials: E
authors.lastname: Sulpice
authors.forename: Jean-Charles
authors.initials: JC
authors.lastname: Leplé
authors.forename: Annabelle
authors.initials: A
authors.lastname: Déjardin
authors.forename: Gilles
authors.initials: G
authors.lastname: Pilate
authors.forename: Guy
authors.initials: G
authors.lastname: Costa
mesh_terms: D000595:Amino Acid Sequence; D003001:Cloning, Molecular; D018744:DNA, Plant / Q000235:genetics; D015870:Gene Expression / Q000235:genetics*; D015971:Gene Expression Regulation, Enzymologic; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010802:Phylogeny; D032107:Populus / Q000201:enzymology* / Q000235:genetics; D014934:Wood / Q000201:enzymology* / Q000235:genetics; D014995:Xylosidases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D018744:DNA, Plant; D014995:Xylosidases