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

Abstract

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.

MULTIPASS, a rice R2R3‐typeMYBtranscription factor, regulates adaptive growth by integrating multiple hormonal pathways

“…OsGLU5 ( OsCEL9A ) and its paralog OsGLU14 ( OsCEL9F ) have been previously reported to be auxin‐inducible genes that are expressed during lateral root formation (Yoshida et al. , ). Thus, OsGLU5 and OsGLU14 are positive regulators of growth whose expression is restricted during abiotic stress.…”

A leucine‐rich repeat receptor‐like kinase gene is involved in the specification of outer cell layers in rice roots

“…OsGLU6 , OsCel9A and OsGLU1 belong to the OsGLU gene family, and both OsGLU6 and OsCel9A are highly expressed in roots. Different from OsGLU6 , OsCel9A is specifically expressed at the lateral root primordia (Yoshida et al. , 2006; Zhou et al.…”

HDG11 upregulates cell-wall-loosening protein genes to promote root elongation in Arabidopsis

“…Four molecular mechanisms for cell-wall loosening are generally accepted. The four wall-loosening agents are expansins (Cosgrove et al , 2002; Yennawar et al , 2006; Won et al , 2010; ZhiMing et al , 2011), xyloglucan endotransglucosylase/hydrolase (XTHs) (Vissenberg et al , 2003, 2005; Osato et al , 2006; Maris et al , 2009; Tominaga-Wada et al , 2009), endo-(1,4)-β- d -glucanase (Yoshida et al , 2006; Zhu et al , 2006; Yang et al , 2011) and hydroxyl radical (•OH) (Schopfer et al , 2002; Liszkay et al , 2003; Muller et al , 2009). …”