Abstract
Uridine diphosphate-glucose dehydrogenase (UGD, EC1.1.1.22 oxidizes UDP-Glc (UDP-D-glucose) to UDP-GlcA (UDP-D-glucuronate), a critical precursor of cell wall polysaccharides. GbUGD6 from Gossypium barbadense is more highly expressed late in the elongation of cotton fibers (15 d post-anthesis (DPA)) and during the stage of secondary cell wall thickening (30 DPA). Subcellular localization analysis in onion epidermis revealed that fluorescently labeled GbUGD6 protein was distributed throughout the cell membrane, as well as the nucleus and vacuoles. Examination of UGD function in Arabidopsis revealed that the antisense GbUGD6 lines had shorter roots, deferred blossoming, compared to wild-type plants. Activities of associated enzymes were also affected by UGD reduction, and biochemical analysis of cell wall samples showed an increase in cellulose levels and a decrease in UGP-GlcA contents. The results of the present study as well as previous studies on UGD support the conclusion that UGD plays a major role in synthesizing polysaccharides synthesis in the cell wall.
Highlights
We examined its functioning in Arabidopsis thaliana, and found that antisense expression of GbUGD6 changed the functioning of the above pathways, suggesting that the gene modulates the biosynthesis of cotton fibers
Green fluorescent protein (GFP) signals from the empty vector control were detected in the cytomembrane and nucleus, pCamE- GbUGD6::green fluorescent protein (GFP) expression was observed in the cell membrane system, including the plasma membrane, nucleus, and vacuoles (Figure 1)
UDP-glucose dehydrogenase (UGD) is the key enzyme for generating UDP-GlcA, the primary precursor of hemicelluloses and pectin polysaccharide in plant cell walls
Summary
Uridine diphosphate-glucuronic acid (UDP-GlcA) is an essential precursor of eukaryotic hemicelluloses and pectin matrix polysaccharides (Diet et al, 2006; Karkonen et al, 2005; Malinova et al, 2014; Seifert, 2004) UDP-galacturonic acid (a pectin precursor) and UDP-xylose (precursor of hemicellulose) are formed through catalysis of UDPGlcA by UDP-d-glucuronic acid 4-epimerase (GAE) and UDP-glucuronic acid decarboxylase (UXS), respectively (Clough and Bent, 1998; Zablackis et al, 1995).Synthesis of UDP-GlcA involves two pathways: nucleotide sugar oxidation (Kuhn et al, 2010) and myo-inositol oxidation (MIO) (Karkonen et al, 2005); it is un-clear which is more important. The UGD enzyme has important functions in tobacco (Nicotiana tabacum) and Zea mays, and its differential expression has been described in Arabidopsis thaliana, poplar (Populus), soybean (Glycine max), and Phaseolus vulgaris (Bindschedler et al, 2005; Johansson et al, 2002; Karkonen et al, 2005; Klinghammer and Tenhaken, 2007; Robertson et al, 1996; Tenhaken and Thulke, 1996). In those cases, UGD expression is higher in
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