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Open Access Publications from the University of California

An unusual xylan in Arabidopsis primary cell walls is synthesised by GUX3, IRX9L, IRX10L and IRX14

  • Author(s): Mortimer, JC
  • Faria-Blanc, N
  • Yu, X
  • Tryfona, T
  • Sorieul, M
  • Ng, YZ
  • Zhang, Z
  • Stott, K
  • Anders, N
  • Dupree, P
  • et al.

© 2015 The Authors The Plant Journal © 2015 John Wiley & Sons Ltd. Summary Xylan is a crucial component of many plant primary and secondary cell walls. However, the structure and function of xylan in the dicotyledon primary cell wall is not well understood. Here, we characterized a xylan that is specific to tissues enriched in Arabidopsis primary cell walls. Unlike previously described xylans, this xylan carries a pentose linked 1-2 to the α-1,2-d-glucuronic acid (GlcA) side chains on the β-1,4-Xyl backbone. The frequent and precisely regular spacing of GlcA substitutions every six xylosyl residues along the backbone is also unlike that previously observed in secondary cell wall xylan. Molecular genetics, in vitro assays, and expression data suggest that IRX9L, IRX10L and IRX14 are required for xylan backbone synthesis in primary cell wall synthesising tissues. IRX9 and IRX10 are not involved in the primary cell wall xylan synthesis but are functionally exchangeable with IRX9L and IRX10L. GUX3 is the only glucuronyltransferase required for the addition of the GlcA decorations on the xylan. The differences in xylan structure in primary versus secondary cell walls might reflect the different roles in cross-linking and interaction with other cell wall components. Significance Statement We have characterised a previously unreported type of xylan, which is a hemicellulose, in the Arabidopsis primary cell wall and shown that GUX3 is specifically responsible for adding the GlcA side chains with a precise spacing pattern. In addition, we have shown that only a subset of the known proteins responsible for xylan backbone elongation, IRX9L, IRX10L and IRX14, are necessary to synthesise this xylan.

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