Plant and Cell Physiology Advance Access originally published online on February 18, 2009
Plant and Cell Physiology 2009 50(4):812-827; doi:10.1093/pcp/pcp025
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This article appears in the following Plant and Cell Physiology issue: Special Issue Articles: Photosynthesis [View the issue table of contents]
The F8H Glycosyltransferase is a Functional Paralog of FRA8 Involved in Glucuronoxylan Biosynthesis in Arabidopsis
1Department of Plant Biology, University of Georgia, Athens, GA 30602, USA
2National Exposure Research Laboratory, US Environmental Protection Agency, Athens, GA 30605, USA
*Corresponding author: E-mail, zhye{at}plantbio.uga.edu; Fax, +1-706-542-1805
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Abstract |
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The FRAGILE FIBER8 (FRA8) gene was previously shown to be required for the biosynthesis of the reducing end tetrasaccharide sequence of glucuronoxylan (GX) in Arabidopsis thaliana. Here, we demonstrate that F8H, a close homolog of FRA8, is a functional paralog of FRA8 involved in GX biosynthesis. The F8H gene is preferentially expressed in xylem cells, in which the secondary walls contain an abundant amount of GX, and the F8H protein is targeted to the Golgi where GX is synthesized. Overexpression of F8H in the fra8 mutant completely complemented the fra8 mutant phenotypes including the secondary wall thickness of fibers and vessels, vessel morphology, GX content and the abundance of the reducing end tetrasaccharide sequence of GX, indicating that F8H shares the same biochemical function as FRA8. Although the f8h mutant alone did not show any detectable cell wall defects, the f8h/fra8 double mutant exhibits an additional reduction in cell wall xylose level, a more severe deformation of vessels and an extreme retardation in plant growth compared with the fra8 mutant. Together, our findings suggest that F8H and FRA8 are functional paralogs and that they function redundantly in GX biosynthesis during secondary wall formation in the xylem.
Keywords: Arabidopsis - Glucuronoxylan biosynthesis - Glycosyltransferase - Secondary wall biosynthesis - Xylan
Abbreviations: CaMV, cauliflower mosaic virus; CFP, cyan fluorescent protein; F8H, FRA8 homolog; fra8, fragile fiber8; GalA, galacturonic acid; GlcA, glucuronic acid; GT, glycosyltransferase; GUS, β-glucuronidase; GX, glucuronoxylan; MALDI-TOF MS, matrix-assisted laser-desorption ionization time-of-flight mass spectrometry; irx8, irregular xylem8; irx9, irregular xylem9; MeGlcA, 4-O-methyl-glucuronic acid; NMR, nuclear magnetic resonance; Rha, rhamnose; YFP, yellow fluorescent protein; Xyl, xylose.
(Received December 23, 2008; Accepted February 9, 2009)
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