OsGLU1 gene encoding a putative membrane-bound endo-1,4-β-D-glucanase，plays an significant role in cell elongation and cell wall metabolism in rice.
The gene OsGLU1(Os03g0329500) encodes a putative membrane-bound endo-1,4-β-D-glucanase, which is highly conserved between monocotyledonous and dicotyledonous plants. Endo-1,4-β-D-glucanase (cellulase) belonging to glycosyl hydrolase 9(GH9) enzymes have been implicated in several aspects of cell wall metabolism in higher plants, including cellulose biosynthesis, degradation, modification of other wall polysaccharides that contain contiguous (1,4)-β-glucosyl residues, and wall loosening during cell elongation. Mutation of OsGLU1 results in a reduction in cell elongation and a decrease in cellulose content but an increase in pectin content, suggesting that OsGLU1 affects the internode elongation and cell wall components of rice plants. Transgenic glu mutants overexpressing the OsGLU1 gene complement the mutation and exhibits the wild-type phenotype, indicating that the OsGLU1 is able to completely rescue the mutant phenotype. In addition, OsGLU1 RNAi plants shows dwarf phenotype as the glu mutant does. These results indicate that OsGLU1 plays important roles in plant cell growth.
The 619-aa OsGLU1 contains a transmembrane domain and a glucanase (EGase) domain showing high similarity with endoglucanase TomCel3 (76%) from tomato and KOR (75%) from Arabidopsis but doesn’t include a predicted cleavable signal peptide, which is present in Clostridium thermocellum endoglucanase (CelD). The OsGLU1 protein also comprise six potential N-glycosylation sites and a conserved polarized targeting signal. All the information reveals that OsGLU1 protein belonged to the type II integral membrane protein anchored in the membrane. It is shown that the mRNA level of OsGLU1 is increased in shoot treated with GA or BR, whereas no significant changes are observed when treated with indole-3-acetic acid, ethylene or abscisic acid. Expression study of OsGLU1 indicates that there are no transcripts of OsGLU1 in the homozygous glu plants. However, the OsGLU1 transcripts are detected in the heterozygous and wild type plants. A genome-wide search of DNA and protein databases reveals that at least 10 OsGLU1-like genes (OsGLU1 to OsGLU10) exist in rice genome localized on different chromosomes. OsGLU1, OsGLU2, OsGLU3 and OsGLU10 show constitutive expression patterns in all the organs tested, including leaf, rachis, root, shoot apex, leaf sheath, and developing flower of rice plants. Nevertheless, the OsGLU4, OsGLU5, OsGLU6, OsGLU9 are abundant only in roots and developing flowers of plants. The other two genes OsGLU7 and OsGLU8 show relatively higher expression in rachis and developing flowers. These different expression patterns suggest multiple functions of these genes in different processes of plant growth and development. Specific and combinational expression of these genes may be essential for the formation or function of a given organ.
Partial functional conservation of KOR in gymnosperms implies that its role in cell wall synthesis dates back to 300 million years ago (Mya), predating angiosperms, which arose 130 Mya, and shows that proteins contributing to proper cellulose deposition are important conserved features of vascular plants.
The endo-1,4-β-D-glucanase gene families from barley (Hordeum vulgare), maize (Zea mays), sorghum (Sorghum bicolor), rice (Oryza sativa) and Brachypodium (Brachypodium distachyon) range in size from 23 to 29 members. Phylogenetic analyses demonstrate variations in clade structure between the grasses and Arabidopsis, and indicate differential gene loss and gain during evolution. Map positions and comparative studies of gene structures allow orthologous genes in the five species to be identified and synteny between the grasses is found to be high. It is also possible to differentiate between homoeologues resulting from ancient polyploidizations of the maize genome.
Recently, Libertini et al. reported that 15 endoglucanase genes are present in rice genome, including the ten OsGLUs discussed above. Based on phylogenetic analysis, the OsGLU family, associating with KOR1, CelD and TomCel3 can be divided into four subfamilies. One cluster contained OsGLU4, OsGLU8, OsGLU12, OsGLU13, OsGLU14 and OsGLU15. Another cluster composed by OsGLU1, OsGLU2, OsGLU3, KOR and CEL3, belongs to the membrane-anchored EGase. Moreover, OsGLU1, OsGLU2 and OsGLU3 in rice has similar expression pattern, suggesting that they possibly have functional redundancy. The third cluster is made up of OsGLU5, OsGLU6, OsGLU7, OsGLU9, OsGLU10 and OsGLU11.The CelD from C. thermocellum doesn’t cluster with any others and thus represented a distinct group. Conservation of the sequence between dicots and monocots suggests a functional specialization preceding the divergence between monocots and dicots in evolution.
Labs working on this gene
1. National Key Lab of Plant Genomics, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences 100101, Beijing, People’s Republic of China
2.Australian Research Council Centre of Excellence in Plant Cell Walls, and the Australian Centre for Plant Functional Genomics, School of Agriculture, Food and Wine, University of Adelaide, South Australia 5064, Australia
3.Department of Wood Science, Faculty of Forestry, The University of British Columbia, 2424 Main Mall, Vancouver, BC, V6T 1Z4 Canada
4.Department of Botany, The University of British Columbia, 6270 University Boulevard, Vancouver, BC, V6T 1Z4 Canada
5.CNAP, Biology Department, University of York, P.O. Box 373, York YO10 5YW, UK
 Zhou, H.L., He, S.J., Cao, Y.R., et al. 2006. OsGLU1, a putative membrane-bound endo-1,4-b-D-glucanase from rice, affects plant internode elongation. Plant Molecular Biology, 60:137-151.
 Buchanan, M., Burton, R.A., Dhugga, K.S., et al. 2012. Endo-(1,4)-β-Glucanase gene families in the grasses: temporal and spatial Co-transcription of orthologous genes. BMC Plant Biology, 12:235-253.
 Maloney, V.J., Samuels, A.L., Mansfield, S.D. 2012. The endo-1,4-b-glucanase Korrigan exhibits functional conservation between gymnosperms and angiosperms and is required for proper cell wall formation in gymnosperms. New Phytologist, 193: 1076-1087.
 Libertini, E., Li, Y. McQueen-Mason, S.J. 2004. Phylogenetic analysis of the plant endo-beta-1,4-glucanase gene family. Journal of Molecular Evolution. 58: 506-515.