Os08g0114200

Os08g0114200 is OsGLU3 which is similar to CEL5=CELLULASE 5 coding a β-1,4-endoglucanase，playing an significant role in root elongation in rice

Annotated Information

Introduce

Endo-1,4-β-D-glucanases (EGases) form a large family of hydrolytic enzymes in prokaryotes and eukaryotes.In higher plants, potential substratesin vivo are xyloglucan and non-crystalline cellulose in the cell wall.Gene expression patterns suggest a role for EGases in various developmental processes such as leaf abscission,fruit ripening and cell expansion. Using Arabidopsis thaliana genetics, scientists demonstrate the requirement of a specialized member of the EGase family for the correct assembly of the walls of elongating cells.KORRIGAN(KOR) is identified by an extreme dwarf mutant with pronounced architectural alterations in the primary cell wall. The KORgene was isolated and encodes a membrane-anchored member of the EGase family, which is highly conserved between mono- and icotyledonous plants. KOR is located primarily in the plasma membrane and presumably acts at the plasma membrane–cell wall interface.KORmRNA was found in all organs examined, and in the developing darkgrown hypocotyl, mRNA levels were correlated with rapid cell elongation. Among plant growth factors involved in the control of hypocotyl elongation (auxin, gibberellins and ethylene) none significantly influenced KOR-mRNA levels. However, reducedKOR-mRNA levels were observed in det2, a mutant deficient for brassinosteroids. Although the in vivo substrate remains to be determined, the mutant phenotype is consistent with a central role for KOR in the assembly of the cellulose–hemicellulose network in the expanding cell wall (4).

Function

The gene OsGLU3 (Os08g0114200), a β-1,4-endoglucanase, can affect the cellulose synthesis for root elongation in rice. And the phosphate starvation induced root elongation in rice depends on the function of OsGLU3 (Os08g0114200). Which was researched that OsGLU3 (Os08g0114200) is also dispensable for nitrogen starvation induced root elongation in rice. The test:The Wild type (WT, SSBM) were grown for 10 d in media without nitrogen and transferred to low nitrogen media (2 mg/L nitrogen) or control media (40 mg/L nitrogen) for another 20d respectively. The nitrogen starvation stress leads to an around 20% increase of primary root elongation in WT as compared with that gro wn under the control condition, Fig1A). It showed that nitrogen starvation can lead to an increase of approximately 13% in rice root cell elongation (Fig1C and E).It also found that the nitrogen starvation can lead to an approximately 15% increase in root cellulose content (Fig1D). It was iden tified phosphate starvation and the nitrogen starvation stimulate primary root elongation by inducing root cell elongation and activating root mitotic activity. It suggests that nitrogen starvation induced primary root elongation depends on the activity of OsGLU3 (Os08g0114200). An OsGLU3(Os08g0114200) dependant way affec t root cell wall cellulose synthesis by modulating root architectureboth in the phosphate or nitrogen starvation in rice.OsGLU3 (Os08g0114200)is a key player in the carbon partitioning system, as loss of function of it can abolish the response (1). The fully functional OsGLU3–GFP was detected in plasma membrane, and FM4-64-labeled compartments in the root meristem and elongation zones .In conclusion, it demonstrated that OsGLU3 was involved in the synthesis of root cellulose and thereby modulate root cell division and elongation in rice. Phosphate starvation, an environmental stress, induces root cellulose synthesis for root elongation, and OsGLU3 is a key player in this process(3).

Mutation

Screeningan ethylmethane sulfonate (EMS) mutagenized rice library, and isolated a short root mutant,Osglu3-1. The map-based cloning results showed that the mutant was due to a point mutation in OsGLU3, which encodes a putative membrane-bound endo-1,4-b-glucanase. Osglu3-1 displayed less crystalline cellulose content in its root cell wall, shorter root cell length, and a slightly smaller root meristem as visualized by restricted expression of OsCYCB1,1:GUS. Exogenous application of glucose can suppress both the lower root cell wall cellulose content and short root phenotypes ofOsglu3-1.The mutant resulted from a mutation in a rice KOR1 homolog OsGLU3, which encodes a putative membranebound endo-1,4-b-glucanase. OsGLU3 can affect root cell wall cellulose synthesis to modulate root elongation. Phosphate starvation, an environmental stress,can modulate root cell wall cellulose synthesis to induce root growth in an OsGLU3-dependent way. the cell length of mature epidermal cells was only one-third of those in the WT, while the root hair length of the mutant is similar to that of WT (Fig 3B and 3C ).The region expressing the OsCYCB1,1:GUSin the root meristem of mutant is about 90% of that in WT (Fig 3D and 3E). Together,these data suggest that the short root phenotype of Osglu3-1results from defects in both root cell elongation and division,particularly defect in cell elongation.the mutation of OsGLU3 might lead to an alteration of cell wall components in root tissue.The results showed that Osglu3-1 had almost the same concentration of cell wall cellulose as WT grown on medium with 3% exogenous glucose. Moreover, the cellulose content of WT and Osglu3-1 had statistically increased after the application of 3% glucose (Fig 3F).The root growth response ofOsglu3-2to glucose treatment was also tested. As with the Osglu3-1 mutant, the application of 3% glucose suppressed the short root and short lateral root defect of Osglu3-2(Fig 3G).Together, these data indicate that OsGLU3 modulates root cell wall cellulose synthesis and affects root cell elongation and division. The exogenous application of glucose can restore the root cell wall cellulose synthesis and rescue the root growth defects of Osglu3 mutants (3).

Expression

In the rice genome, endo-1,4-b-D-glucanases form a multiple gene family including OsGLU3 which share high sequence similarity with KOR1 (2). OsGLU3is ubiquitously expressed in various tissues with strong expression in root tip, lateral root, and crown root primodia. OsGLU3contains four exons and three introns (Fig 2B). The putative OsGLU3 was predicted to contain a transmembrane domain, a cytosolic domain, and a catalytic domain (Supplemental Fig 3A). The mutation is located in the catalytic domain, which is highly conserved among the plant KOR1 homologs (Supplemental Fig 3B). qRT–PCR showed that the OsGLU3 is highly expressed in root tissue and has relatively lower expression in the other tissues. The OsGLU3–GUS expression was observed ubiquitously in the rice plants included in leaf veins, excoemums,and roots. the OsGLU3–GFP protein may reflect the native OsGLU3.OsGLU3 localizes in the plasma member and endosomes, and the export of OsGLU3 to the PM depends on vesicle transport. Phosphate starvation could induce root elongation inOsglu3-1.The phosphate starvation-induced primary root elongation and cellulose-content increase are abolished in Osglu3-2, which suggests that phosphate starvation-induced primary root elongation depends on the activity of OsGLU3.Suggesting that a single recessive gene was responsible for the mutant phenotype. Using 1 000 F2 mutant seedlings selected from the population, the mutation was mapped to a 56-kb region between S4-24837K and S4-24893K on chromosome 4. This region contains 14 open reading frames (ORFs), including a b-1,4-endoglucanase (OsGLU3, LOC_Os04g41970)(3).

Evolution

Please input evolution information here.

In rice genome, the putative membrane-anchored endo-b-1,4-D-glucanases were encoded by three genes: OsGLU1, OsGLU2, and OsGLU3.Recently,Libertiniet al.(2004) reported that 15 endoglucanase genes were present in rice genome.that these proteins could be classified into four main clusters. One cluster contained OsGLU4, OsGLU8, OsGLU12, OsGLU13,OsGLU14 and OsGLU15. Another cluster contained OsGLU1, OsGLU2, OsGLU3, KOR and CEL3. The third cluster contained OsGLU5,OsGLU6, OsGLU7, OsGLU9, OsGLU10 and OsGLU11.OsGLU1to OsGLU10 each gene had different numbers of introns and exons. All proteins of the OsGLU family contained the EGase domain. The OsGLU1, OsGLU2 and OsGLU3 contained a predicted highly hydrophobic transmembrane motif in the N-terminal and belonged to the type II integral membrane protein anchored in the membrane. The results demonstrated thatOsGLU1, OsGLU2,OsGLU3 and OsGLU10 showed constitutive expression patterns in all the organs tested, and the OsGLU4, OsGLU5, OsGLU6, OsGLU9were abundant in roots and developing flowers of plants. The other two genes OsGLU7 and OsGLU8 showed relatively higher expression in rachis and developing flowers. These different expression patterns indicated 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（2）.

Discussion

The Osglu3-1 mutant has less cellulose in its roots and is defective in root cell elongation and division. However,theshoot development ofOsglu3-1seems ormal. In rice genome, the putative membrane-anchored endo-b-1,4-D-glucanases were encoded by three genes: OsGLU1, OsGLU2, and OsGLU3. Although all of them are expressed ubiquitously in the rice plant,OsGLU1 showed high expression in shoot tissue whilstOsGLU3is highly expressed inroot tissue.This indicates that the different expression pattern of the gene members might explain the root elongation defect of Osglu3-1. Consistently with this,the mutation of OsGLU1 also resulted in a reduction in shoot cell growth(2). In our study, the exogenous glucose inhibits the primary root elongation in the WT, which might due to the osmotic stress or the glucose serving as a signal. However, it could completely restore the mutant phenotype ofOsglu3-1and partially restore the phenotype of Osglu3-2. There were two possible explanations for this phenomenon. One is that OsGLU3 might function in trimming sterol residues from nascent glucan primers. When glucose, the substrate of cellulose synthesis, is added, it leads to an increase in the glucan chain.The addition of the glucan chains together with the residual OsGLU3 enzymatic activity of the point mutation mutant could restore the phenotypic defects ofOsglu3-1. However, this explanation could not explain the partial complementation of the loss-of-function mutantOsglu3-2by the exogenous glucose. The other possibility is that OsGLU3 might hydrolyze the matrix polysaccharides or the links between matrix polysaccharides and, together with cell wall-loosening enzymes (such as expansins), create space for new synthesis cellulose.Exogenous glucose leads to an induction of cellulose synthesis,which needs more space(3).

Labs working on this gene

1.National Key Lab of Plant Genomics,People’s Republic of China. 2.Institute of Genetics and Developmental Biology, Chinese Academy of Sciences ,People’s Republic of China. 3.The State Key Laboratory of Plant Physiology and Biochemistry, College of Life Science, Zhejiang University,People’s Republic of China. 4.College of Science and Technology, Ningbo University, Ningbo, Zhejiang , China. 5.State Key Laboratory Breeding Base for Zhejiang Sustainable Pest and Disease Control, People’s Republic of China. 6.Institute of Virology and Biotechnology, Zhejiang Academy of Agricultural Sciences, Hangzhou , People’s Republic of China. 7.Laboratoire de Biologie Cellulaire, Institut National de RechercheAgronomique 8.Universite´ de Rouen, CNRS UPRESA 6307, Faculte´ des Sciences 9.Centre de Physiologie Ve´ge´tale de l’Universite ´ Paul Sabatier, U.A.

References

1. Zhang J, Xu L, Wang F, Deng M, Yi K. Modulating the root elongation by phosphate/nitrogen starvation in an OsGLU3 dependant way in rice. Plant signaling & behavior. 2012;7(9):1144-5. 2. Zhou HL, He SJ, Cao YR, Chen T, Du BX, Chu CC, et al. OsGLU1, a putative membrane-bound endo-1,4-beta-D-glucanase from rice, affects plant internode elongation. Plant molecular biology. 2006;60(1):137-51. 3. Zhang JW, Xu L, Wu YR, Chen XA, Liu Y, Zhu SH, et al. OsGLU3, a putative membrane-bound endo-1,4-beta-glucanase, is required for root cell elongation and division in rice (Oryza sativa L.). Mol Plant. 2012;5(1):176-86. 4. Fre´de´ ric Nicol1, Isabelle His, Alain Jauneau, Samantha Vernhettes, Herve´ Canut, Herman Ho¨ fte. A plasma membrane-bound putative endo-1,4-betaD-glucanase is required for normal wall assembly and cell elongation inArabidopsis. The EMBO Journal. 1998;17(19):5563-76.