Journal Article

Carbohydrate-Binding Module of a Rice Endo-β-1,4-glycanase, <i>OsCel9A</i>, Expressed in Auxin-Induced Lateral Root Primordia, is Post-Translationally Truncated

Kouki Yoshida, Nobuyuki Imaizumi, Satoshi Kaneko, Yasushi Kawagoe, Akemi Tagiri, Hiroshi Tanaka, Kazuhiko Nishitani and Kozo Komae

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 47, issue 11, pages 1555-1571
Published in print November 2006 | ISSN: 0032-0781
Published online November 2006 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcl021
Carbohydrate-Binding Module of a Rice Endo-β-1,4-glycanase, OsCel9A, Expressed in Auxin-Induced Lateral Root Primordia, is Post-Translationally Truncated

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We report the cloning of a glycoside hydrolase family (GHF) 9 gene of rice (Oryza sativa L. cv. Sasanishiki), OsCel9A, corresponding to the auxin-induced 51 kDa endo-1,4-β-glucanase (EGase). This enzyme reveals a broad substrate specificity with respect to sugar backbones (glucose and xylose) in β-1,4-glycans of type II cell wall. OsCel9A encodes a 640 amino acid polypeptide and is an ortholog of TomCel8, a tomato EGase containing a carbohydrate-binding module (CBM) 2 sequence at its C-terminus. The expression of four rice EGase genes including OsCel9A showed different patterns of organ specificity and responses to auxin. OsCel9A was preferentially expressed during the initiation of lateral roots or subcultured root calli, but was hardly expressed during auxin-induced coleoptile elongation or in seed calli, in contrast to OsCel9D, a KORRIGAN (KOR) homolog. In situ localization of OsCel9A transcripts demonstrated that its expression was specifically up-regulated in lateral root primordia (LRP). Northern blotting analysis showed the presence of a single product of OsCel9A. In contrast, both mass spectrometric analyses of peptide fragments from purified 51 kDa EGase proteins and immunogel blot analysis of EGase proteins in root extracts using two antibodies against internal peptide sequences of OsCel9A revealed that the entire CBM2 region was post-translationally truncated from the 67 kDa nascent protein to generate 51 kDa EGase isoforms. Analyses of auxin concentration and time course dependence of accumulation of two EGase isoforms suggested that the translation and post-translational CBM2 truncation of the OsCel9A gene may participate in lateral root development.

Keywords: Auxin; Carbohydrate-binding module family 2; Glycoside hydrolase family 9; Lateral root formation; Processing; Rice

Journal Article.  10962 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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