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CesA genes are believed to encode the catalytic subunit of cellulose synthase. Identification of nine distinct CesA cDNAs from maize (Zea mays) has allowed us to initiate comparative studies with homologs from Arabidopsis and other plant species. Mapping studies show that closely related CesA genes are not clustered but are found at different chromosomal locations in both Arabidopsis and maize. Furthermore, sequence comparisons among the CesA-deduced proteins show that these cluster in groups wherein orthologs are often more similar than paralogs, indicating that different subclasses evolved prior to the divergence of the monocot and dicot lineages. Studies using reverse transcriptase polymerase chain reaction with gene-specific primers for six of the nine maize genes indicate that all genes are expressed to at least some level in all of the organs examined. However, when expression patterns for a few selected genes from maize and Arabidopsis were analyzed in more detail, they were found to be expressed in unique cell types engaged in either primary or secondary wall synthesis. These studies also indicate that amino acid sequence comparisons, at least in some cases, may have value for prediction of such patterns of gene expression. Such analyses begin to provide insights useful for future genetic engineering of cellulose deposition, in that identification of close orthologs across species may prove useful for prediction of patterns of gene expression and may also aid in prediction of mutant combinations that may be necessary to generate severe phenotypes.
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PMID:A comparative analysis of the plant cellulose synthase (CesA) gene family. 1093 50

Recent molecular genetic data suggest that cellulose synthase (CesA) genes coding for the enzymes that catalyze cellulose biosynthesis (CESAs) in Arabidopsis and other herbaceous plants belong to a large gene family. Much less is known about CesA genes from forest trees. To isolate new CesA genes from tree species, discriminative but easily obtainable homologous DNA probes are required. Hypervariable regions (HVRII) of CesA genes represent highly divergent DNA sequences that can be used to examine structural, expressional and functional relationships among CesA genes. We used a reverse transcriptase-polymerase chain reaction (RT-PCR)-based technique to identify HVRII regions from eight types of CesA genes and two types of CesA-like D (CslD) genes in quaking aspen (Populus tremuloides Michx.). Comparison of these aspen CESA/CSLD HVRII regions with the predicted proteins from eight full-length CesA/CslD cDNAs available in our laboratory and with searches for aspen CesA/CslD homologs in the recently released Populus trichocarpa Torr. & A. Gray. genome confirmed the utility of this approach in identifying several CesA/CslD gene members from the Populus genome. Phylogenetic analysis of 56 HVRII domains from a variety of plant species suggested that at least six distinct classes of CESAs exist in plants, supporting a previous proposal for renaming HVRII regions as class-specific regions (CSR). This method of CSR cloning could be applied to other crop plants and tree species, especially softwoods, for which the whole genome sequence is unlikely to become available in the near future because of the large size of these genomes.
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PMID:Molecular cloning of ten distinct hypervariable regions from the cellulose synthase gene superfamily in aspen trees. 1499 58

Based on elegant molecular genetic analyses, distinct classes of cellulose synthase (CesA) genes have been associated with either primary or secondary cell wall development in Arabidopsis. Here, we report on cloning of two new CesA cDNAs, PtrCesA6 and PtrCesA7 involved in the primary cell wall development in aspen (Populus tremuloides) trees. Both these distinct cDNAs, isolated from a developing xylem cDNA library, share only 60-67% identities with each other as well as with five other previously known aspen CesA cDNAs. Interestingly, PtrCESA6 from aspen, a dicot species, shares maximum identity of 81-84% with three CESA isoforms from maize and rice, two monocot species. On the other hand, PtrCESA7 shares a maximum identity of 86% with AtCESA2, a primary wall-related CesA member from Arabidopsis, a dicot species. Gene expression analyses by reverse transcriptase-polymerase chain reactions (RT-PCRs) suggested that both these genes are expressed at a low level in all aspen tissues examined but PtrCesA7 is expressed at a higher level than PtrCesA6. While corroborating these results, in situ mRNA hybridization studies using three different aspen organs also suggested that PtrCesA6 and PtrCesA7 genes are expressed in all expanding cells depositing primary cell wall but PtrCesA7 is expressed at a higher level than PtrCesA6. These differential gene expression profiles suggest that each of these CesAs may be playing a specific role during primary cell wall development in aspen trees. Isolation of two primary wall related CesA genes from xylem tissues also suggest their importance during xylem development, which is traditionally considered to be enriched in secondary cell wall forming cells of economical significance.
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PMID:Differential expression patterns of two new primary cell wall-related cellulose synthase cDNAs, PtrCesA6 and PtrCesA7 from aspen trees. 1525 57

Loblolly pine (Pinus taeda L.), the most widely planted tree species in the United States, is an important source of wood and wood fibers for a multitude of consumer products. Wood fibers are primarily composed of secondary cell walls, and cellulose, hemicelluloses and lignin are major components of wood. Fiber morphology and cell wall composition are important determinants of wood properties. We used comparative genomics to identify putative genes for cellulose and hemicellulose synthesis in loblolly pine that are homologous to genes implicated in cell wall synthesis in angiosperms. Sequences encoding putative secondary cell wall cellulose synthase genes, cellulose synthase-like genes, a membrane-bound endoglucanase gene, a sucrose synthase gene, a UDP-glucose pyrophosphorylase gene and GDP-mannose pyrophosphorylase genes were identified in expressed sequence tag (EST) collections from loblolly pine. Full-length coding sequences were obtained from cDNA clones isolated from a library constructed from developing xylem. Phylogenetic relationships between the genes from loblolly pine and angiosperm taxa were examined and transcriptional profiling in vascular tissues was conducted by real-time quantitative, reverse transcriptase-polymerase chain reaction. The putative cell wall synthesis genes were expressed at high levels in vascular tissues and a subset was differentially regulated in xylem and phloem tissues. Inferred phylogenetic relationships and expression patterns for the genes from loblolly pine were consistent with roles in synthesis of complex carbohydrates of the cell wall. These studies suggest functional conservation of homologous wood formation genes in gymnosperm and angiosperm taxa.
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PMID:Carbohydrate-related genes and cell wall biosynthesis in vascular tissues of loblolly pine (Pinus taeda). 1845 May 74