title: Xyloglucan endotransglycosylases have a function during the formation of secondary cell walls of vascular tissues.
abstract: Xyloglucan transglycosylases (XETs) have been implicated in many aspects of cell wall biosynthesis, but their function in vascular tissues, in general, and in the formation of secondary walls, in particular, is less well understood. Using an in situ XET activity assay in poplar stems, we have demonstrated XET activity in xylem and phloem fibers at the stage of secondary wall formation. Immunolocalization of fucosylated xylogucan with CCRC-M1 antibodies showed that levels of this species increased at the border between the primary and secondary wall layers at the time of secondary wall deposition. Furthermore, one of the most abundant XET isoforms in secondary vascular tissues (PttXET16A) was cloned and immunolocalized to fibers at the stage of secondary wall formation. Together, these data strongly suggest that XET has a previously unreported role in restructuring primary walls at the time when secondary wall layers are deposited, probably creating and reinforcing the connections between the primary and secondary wall layers. We also observed that xylogucan is incorporated at a high level in the inner layer of nacreous walls of mature sieve tube elements.
authors.affiliation: Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden.
authors.forename: Veronica
authors.initials: V
authors.lastname: Bourquin
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Nishikubo
authors.forename: Hisashi
authors.initials: H
authors.lastname: Abe
authors.forename: Harry
authors.initials: H
authors.lastname: Brumer
authors.forename: Stuart
authors.initials: S
authors.lastname: Denman
authors.forename: Marlin
authors.initials: M
authors.lastname: Eklund
authors.forename: Maria
authors.initials: M
authors.lastname: Christiernin
authors.forename: Tunla T
authors.initials: TT
authors.lastname: Teeri
authors.forename: Björn
authors.initials: B
authors.lastname: Sundberg
authors.forename: Ewa J
authors.initials: EJ
authors.lastname: Mellerowicz
mesh_terms: D000595:Amino Acid Sequence; D002454:Cell Differentiation / Q000235:genetics / Q000502:physiology; D002473:Cell Wall / Q000201:enzymology / Q000235:genetics / Q000502:physiology; D003001:Cloning, Molecular; D016695:Glycosyltransferases / Q000235:genetics* / Q000378:metabolism*; D007150:Immunohistochemistry; D016253:Microscopy, Immunoelectron; D008969:Molecular Sequence Data; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000201:enzymology / Q000235:genetics / Q000254:growth & development; D018514:Plant Structures / Q000201:enzymology / Q000235:genetics / Q000254:growth & development* / Q000648:ultrastructure; D032107:Populus / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development
chemical_list: D010940:Plant Proteins; D016695:Glycosyltransferases; C073693:xyloglucan endotransglycosylase