Abstract
Cellulose synthase (CESA), which is an essential catalyst for the generation of plant cell wall biomass, is mainly encoded by the CesA gene family that contains ten or more members. In this study; four full-length cDNAs encoding CESA were isolated from Betula platyphylla Suk., which is an important timber species, using RT-PCR combined with the RACE method and were named as BplCesA3, −4, −7 and −8. These deduced CESAs contained the same typical domains and regions as their Arabidopsis homologs. The cDNA lengths differed among these four genes, as did the locations of the various protein domains inferred from the deduced amino acid sequences, which shared amino acid sequence identities ranging from only 63.8% to 70.5%. Real-time RT-PCR showed that all four BplCesAs were expressed at different levels in diverse tissues. Results indicated that BplCESA8 might be involved in secondary cell wall biosynthesis and floral development. BplCESA3 appeared in a unique expression pattern and was possibly involved in primary cell wall biosynthesis and seed development; it might also be related to the homogalacturonan synthesis. BplCESA7 and BplCESA4 may be related to the formation of a cellulose synthase complex and participate mainly in secondary cell wall biosynthesis. The extremely low expression abundance of the four BplCESAs in mature pollen suggested very little involvement of them in mature pollen formation in Betula. The distinct expression pattern of the four BplCesAs suggested they might participate in developments of various tissues and that they are possibly controlled by distinct mechanisms in Betula.
Highlights
Cellulose, a key structural component of the plant cell wall, is the most abundant biopolymer in the world
A search for conserved domains or functional motifs in the CDD revealed that the four encoded proteins possessed two separate conserved domains: a glycosyltransferase domain (E value = 2 × 10−11) and a cellulose synthase domain, which are typical of CESAs (E value 1.0 × 10−180) [2,4]
BplCesA3, −4, −7 and −8, using the three-letter prefix nomenclature (Bpl) for cellulose synthase genes reported in Populus [23]
Summary
A key structural component of the plant cell wall, is the most abundant biopolymer in the world. Cellulose is a homopolymer consisting of β-1,4-glucan chains that are synthesized at the plasma membrane by membrane-localized “rosette” complexes [1], as visualized by freeze-fracture electron microscopy [2,3,4,5]. Cellulose synthase (CESA) has been localized in these cellulose-synthesizing complexes. Each plant synthesizes a number of different cellulose synthases and each cellulose-synthesizing complex contains at least three non-redundant cellulose synthase isoforms. Both genetic and biochemical evidence suggest that different CESA isoforms interact to form a functional cellulose synthase enzyme complex [7]. CesA genes are part of a CesA/CSL superfamily, and the proteins they encode contain the same domains and regions as CESA proteins of coniferous gymnosperms [8], angiosperms and molds [9]
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