title: Function of xyloglucan endotransglucosylase/hydrolases in rice.
abstract: OBJECTIVE
  Although xyloglucans are ubiquitous in land plants, they are less abundant in Poales species than in eudicotyledons. Poales cell walls contain higher levels of β-1,3/1,4 mixed-linked glucans and arabinoxylans than xyloglucans. Despite the relatively low level of xyloglucans in Poales, the xyloglucan endotransglucosylase/hydrolase (XTH) gene family in rice (Oryza sativa) is comparable in size to that of the eudicotyledon Arabidopsis thaliana. This raises the question of whether xyloglucan is a substrate for rice XTH gene products, whose enzyme activity remains largely uncharacterized.
  
  
  METHODS
  This study focused on OsXTH19 (which belongs to Group IIIA of the XTH family and is specifically expressed in growing tissues of rice shoots), and two other XTHs, OsXTH11 (Group I/II) and OsXTH20 (Group IIIA), for reference, and measurements were made of the enzymatic activities of three recombinant rice XTHs, i.e. OsXTH11, OsXTH20 and OsXTH19.
  
  
  RESULTS
  All three OsXTH gene products have xyloglucan endohydrolase (XEH, EC 3·2·1·151) activity, and OsXTH11 has both XEH and xyloglucan endotransglycosylase (XET, EC 2·4·1207) activities. However, these proteins had neither hydrolase nor transglucosylase activity when glucuronoarabinoxylan or mixed-linkage glucan was used as the substrate. These results are consistent with histological observations demonstrating that pOsXTH19::GUS is expressed specifically in the vicinity of tissues where xyloglucan immunoreactivity is present. Transgenic rice lines over-expressing OsXTH19 (harbouring a Cauliflower Mosaic Virus 35S promoter::OsXTH19 cDNA construct) or with suppressed OsXTH19 expression (harbouring a pOsXTH19 RNAi construct) did not show dramatic phenotypic changes, suggesting functional redundancy and collaboration among XTH family members, as was observed in A. thaliana.
  
  
  CONCLUSIONS
  OsXTH20 and OsXTH19 act as hydrolases exclusively on xyloglucan, while OsXTH11 exhibits both hydrolase and XET activities exclusively on xyloglucans. Phenotypic analysis of transgenic lines with altered expression of OsXTH19 suggests that OsXTH19 and related XTH(s) play redundant roles in rice growth.
authors.affiliation: Department of Developmental Biology and Neurosciences, Graduate School of Life Sciences, Tohoku University, Sendai, 980-8578, Japan.
authors.forename: Yoshinao
authors.initials: Y
authors.lastname: Hara
authors.affiliation: Department of Developmental Biology and Neurosciences, Graduate School of Life Sciences, Tohoku University, Sendai, 980-8578, Japan.
authors.forename: Ryusuke
authors.initials: R
authors.lastname: Yokoyama
authors.affiliation: Center for Collaboration among Agriculture, Industry and Commerce, University of Tokushima, Tokushima, 770-8501 Japan.
authors.forename: Keishi
authors.initials: K
authors.lastname: Osakabe
authors.affiliation: Plant Genome Engineering Research Unit, National Institute of Agrobiological Sciences, Kannondai, Tsukuba, Ibaraki, 305-8602, Japan.
authors.forename: Seiichi
authors.initials: S
authors.lastname: Toki
authors.affiliation: Department of Developmental Biology and Neurosciences, Graduate School of Life Sciences, Tohoku University, Sendai, 980-8578, Japan nishitan@m.tohoku.ac.jp.
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Nishitani
mesh_terms: D002473:Cell Wall / Q000378:metabolism*; D005936:Glucans / Q000378:metabolism; D016695:Glycosyltransferases / Q000235:genetics / Q000378:metabolism*; D012275:Oryza / Q000201:enzymology* / Q000235:genetics; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D014990:Xylans / Q000378:metabolism
chemical_list: D005936:Glucans; D010940:Plant Proteins; D014990:Xylans; C114470:glucuronoarabinoxylan; C029353:xyloglucan; D016695:Glycosyltransferases; C073693:xyloglucan endotransglycosylase; C473049:xyloglucan - xyloglucosyltransferase
keywords: Oryza sativa; Poales; XTH; cell wall; xyloglucan endohydrolase; xyloglucan endotransglucosylase