Os10g0467800

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Annotated Information

Function

Cellulose is the major component in wood, which is present universally in plant cell walls and provides mechanical strength to the plant. Cellulose accounts for about 20 % and 50 % of the primary and secondary cell walls in higher plants, respectively. Membrane-bound cellulose synthase enzyme complexes (CelS) are believed to play a key role in the biosynthesis of cellulose. These complexes are discernible as hexameric rosettes under freeze-fracture electron microscopy and consist of 36 cellulose synthase (CesA) proteins per rosette.The AtCesA7 gene encodes a essential subunit which is required for the correct assembly of the enzyme responsible for cellulose synthesis. Cellulose is a homogenous polymer of β-1,4-glucan synthesized from UDP-Glc. Plant CesA (cellulose synthase catalytic subunit) genes were first isolated by random sequencing of cotton (Gossypium hirsutum) expressed sequence tags. Based on mutant analyses, characterization of six CesA genes of Arabidopsis has been reported. But cellulose biogenesis is a complex process, which still requires ongoing study to comprehend completely its pathways and mechanisms. Even with the completion of the Arabidopsis thaliana genome sequencing project, researchers still struggle to understand the biogenesis of cellulose in A.thaliana，let alone other plants that are less well studied.

Expression

OsCesA7 cDNA,including 9 exons, encoding a 1063 amino acid composition of cellulose synthase catalytic subunit. OsCesA7 contains a UDP - Glc motif,QxxRW motif,P - CR conservative domain,VR1 and VR2 variable region,the RING finger motif. The rsw1 mutation in AtCesA1 causes a reduction of cellulose synthesis, when grown at the nonpermissive temperature, resulting in disassembly of the rosette complexes,widespread morphological abnormalities, and the accumulation of noncrystalline β-1,4-glucan. The irx3 mutant of AtCesA7 shows a reduction of cellulose content in the stem and a defect in the secondary cell wall formation in xylem that causes collapse of xylem elements. These results indicate that AtCesA1 and AtCesA7 contribute to cellulose syntheses in the properly developed primary and secondary cell wall,respectively.

Based on the sequences shown in Figure 3, phylogenetic relationships of CesA genes from higher plants were examined (Fig. 4). Three rice CesA genes were considered to function to synthesize cellulose in the secondary cell walls responsible for the overall strength of the plant, judging from the brittle culm phenotype (Fig. 1) exhibited by their respective mutants (Fig. 2).

Figure 1. Phenotypes of the five rice brittle culm mutants. A, Plant heights of the wild-type plant (1) and the mutants of NC0259 (2), ND8759 (3), NE1031 (4), ND2395 (5), and NF1011 (6). B, Brittleness of culm (C) and mature leaf (L) from wild-type plant (W) and the mutant (M) as demonstrated by the damage caused by stressing between fingers. Numbers indicate mutant lines as described above. All culms were prepared from the second internodes.

Figure 2. An external file that holds a picture, illustration, etc.Genomic structure of three rice CesA genes, OsCesA4, -7, and -9. The black boxes and lines indicate exon and intron sequences, respectively. Scale bar = 1 kb. Arrows and numbers indicate the Tos17 insertion sites and mutant lines, respectively.

Figure 3. An external file that holds a picture, illustration, etc.Alignment of the deduced amino acid sequences of OsCesA4, -7, and -9. Numbers indicate the position of the amino acid residues of each protein. The residues that are identical in at least two CesA genes are marked in reverse contrast letters. The three Asp (D) residues and the QxxRW motif that are critical for the function of CESA (see text) are marked by asterisks. The plant conserved region (P-CR), variable regions (VR1 and -2), and RING finger motif are also shown by overhead double-dashed lines.

Figure 4. Phylogenetic relationships of CesA genes from higher plants. Phylogenetic trees based on the complete amino acid sequences were generated by using ClustalX (version 1.8), then bootstrapping at random number generator seed = 1,000 and number of bootstrap trials = 10,000. Plant species are as follows: At, Arabidopsis; Gc, cotton; Os, rice; Pc, Populus × canescens; Ptr, Populus tremuloides; and Zm, maize.

The phylogenetic relationships between the three rice CesA genes and all of the Arabidopsis genes indicated that OsCesA9, OsCesA4, and OsCesA7 are the functional analogues for AtCesA7, AtCesA8, and AtCesA4, respectively. This result strongly suggests that these three rice CESA proteins, like the three Arabidopsis CESA proteins, make a complex essential for cellulose synthesis in secondary cell wall. Two cotton CesA genes (GhCesA1 and -3) that are considered to be members of secondary wall-forming genes belong to the same group including OsCesA4 and AtCesA8. In maize, only eight complete amino acid sequences have been determined, and no CesA genes analogous to the three rice/Arabidopsis genes have been isolated, probably due to low abundance of the cDNAs.

Evolution

Analyze the cellulose synthase gene family of rice by using the DNAStar and MEGA software, The results show that cellulose synthase gene family is formed by the cellulose synthase family which is make up of eleven members and  the cellulose synthaselike family which including thirtyfour members, By Protein sequence alignment and  phylogenetic analysis,we know that the family of CesA can divided into three groups .the member CesA7 can be seen  as the transition of the group one and group two ,The family of Csl can be divided into six groups, This results  laiding a foundation on origin, evolution and function research of ccellulose synthase gene family.

Figure 5. The phylogenetic tree of distinct rice cellulose synthase catalytic subunit genes required for cellulose synthesis.

Labs working on this gene

In 2000, Richmond and Somerville identified 10 CesA genes and 31 cellulose synthases-like (Csl) genes in Arabidopsis, which were further classified into one CesA family and six Csl families (CslA/B/C/D/E/G) based on phylogenetic analyses . Since then, the whole CesA and Csl gene repertoire has been cataloged in fully sequenced plants, including rice , poplar and the moss Physcomitrella patens . Additional CesA and Csl genes have also been found in diverse and not fully sequenced land plants such as maize , barley and pine; CesAs have been identified in streptophyte green algae such as Mesotaenium caldariorum and in red alga Porphyra yezoensis as well. Two additional Csl families (CslF and CslH) were found in these studies; together with the other six Csl families and one CesA family, they comprise the CesA superfamily.

The phylogenetic classification and the function of the CesA superfamily were reviewed by Lerouxel et al. in 2006 , and since then there have been a few updates in terms of the phylogenetic analyses of these important genes. Fincher et al. have found a new Csl family (CslJ) in cereals . Roberts and Bushoven have mined the P. pattens genomic and EST data and found CesA, CslA, CslC and CslD genes in this lower plant; their phylogenetic analyses revealed that seven P. patens CesA genes form a monophyletic clade by themselves and there are no one-to-one orthologs in the moss corresponding to the Arabidopsis CesA triplet subunits (CesA1/3/6 for the primary cell wall and CesA4/7/8 for the secondary cell wall). Furthermore, comprehensive phylogenetic analyses of the plant CesA superfamily by including CesAs from other organismal groups (e.g., bacteria, fungi and animals) indicated that plant CslA and CslC genes have a different origin than the remaining plant genes . Evidences have been reported that these remaining genes of the CesA superfamily were anciently acquired from cyanobacteria. It was proposed that the plant CslG genes evolved first, followed by the CslE, CslB, CesA and CslD/F genes. However, a more recent study could not find homologs of the CslG/E/B/H/F genes in P. patens, suggesting that these Csl families are narrowly distributed and unlikely to be the earliest evolved.

To date 17 plant and algal genomes have been fully or nearly fully sequenced, and their gene prediction and annotation are publicly available. The availability of these genomes and their annotated genes facilitates comparative genomic studies of plants, making it possible to address major plant biology questions in silico. Yanbin Yin et al. have performed comparative analyses of the CesA superfamily genes in the 17 sequenced plant and algal genomes. They defined CesA and Csl gene homologs across these genomes investigated the evolution of different Csl gene families，build a catalog of all the Csl genes and classified them phylogenetically. The gene structure, the evolutionary rate, and the distribution of the Csl families across different genomes are also studied.