The Arabidopsis irregular xylem8 Mutant Is Deficient in Glucuronoxylan and Homogalacturonan ...

The Arabidopsis irregular xylem8 Mutant Is Deficient in Glucuronoxylan and Homogalacturonan ...

20 Pages · 2007 · 2.49 MB · English

The secondary cell wall in higher plants consists mainly of cellulose, lignin, and xylan and is the major component of biomass in many species. The Arabidopsis thaliana irregular xylem8 (irx8) mutant is dwarfed and has a significant reduction in secondary cell wall thickness. IRX8 belongs to a subg

The Arabidopsis irregular xylem8 Mutant Is Deficient in Glucuronoxylan and Homogalacturonan ... free download

TheArabidopsis irregular xylem8 Mutant Is De?cient in Glucuronoxylan and Homogalacturonan, Which Are Essential for Secondary Cell Wall Integrity W Staffan Persson, aKerry Hosmer Caffall, bGlenn Freshour, bMatthew T Hilley, bStefan Bauer, a Patricia Poindexter, aMichael G Hahn, bDebra Mohnen, band Chris Somerville a , c , 1 aCarnegie Institution, Stanford, California 94305bComplex Carbohydrate Research Center, Unive rsity of Georgia, Athens, Georgia 306024712cDepartment of Biological Sciences, Stanford University , Stanford, California 94305 The secondary cell wall in higher plants consists mainly of cellulose, lignin, and xylan and is the major component of biomass in many species The Arabidopsis thaliana irregular xylem8 (irx8 ) mutant is dwarfed and has a signi?cant reduction in secondary cell wall thickness IRX8 belongs to a subgroup of glycosyltransferase family 8 called the GAUT1related gene family, whose members include GAUT1, a homogalacturonan galacturonosyltransferase, and GAUT12 (IRX8) Here, we use comparative cell wall analyses to show that the irx8mutant contains signi?cantly reduced levels of xylan and homogalacturonan Immuno histochemical analyses con?rmed that the level of xylan was signi?cantly reduced in the mutant Structural ?ngerprinting of the cell wall polymers further revealed that irx8is de?cient in glucuronoxylan To explore the biological function of IRX8,we crossed irx8with irx1(affecting cellulose synthase 8) The homozygous irx1 irx8exhibited severely dwarfed phenotypes, suggesting that IRX8is essential for cell wall integrity during cellulose de?ciency Taken together, the data presented show that IRX8 affects the level of glucuronoxylan and homogalacturonan in higher plants and that IRX8provides an important link between the xylan polymer and the secondary cell wall matrix and directly affects secondary cell wall integrity INTRODUCTION The vascular bundles, harboring phloem and xylem elements, facilitate nutrient and water distribution in higher plants (Ye, 2002) The xylem elements transport water from the root to the aerial parts of the plant The rapid movement of water through the xylem elements creates an internal negative pressure To with stand these forces, the xylem cells deposit a secondary cell wall matrix, mainly consisting of cellulose, lignin, xylan, and a variety of glycoproteins The deposition of the secondary wall occurs when the cells have reached their terminal morphological state (Turner et al, 2001) This ligni?ed secondary wall is the most abun dant element of biomass produced by many plants and also constitutes the major mechanical support for plant growth Defects in the constituents of the secondary cell wall may result in an inward collapse of individual xylem cells (Turner and Somerville, 1997; Turner et al, 2001) Genetic screens for such phenotypes in Arabidopsis thaliana have revealed several genes essential for xylem development, referred to as irregular xylem(irx ) mutants (Turner and Somerville, 1997) or fragile ?ber(fra ) mutants (Zhong et al, 2001) Three of the mutants, irx1,irx3 ,and irx5, have defects in cellulose synthase (CESA) subunits of the secondary cell wall cellulose complex (Turner and Somerville, 1997; Taylor et al, 1999) Several other irxand framutants are associated with cellulose and lignin deposition and with signal transduction?associated processes (Jones et al, 2001; Szyjanowicz et al, 2004; Zhong et al, 2005a) Xylan is the main hemicellulosic component of the secondary cell wall in dicot plants and the second most abundant biopoly mer in plants (Ebringerova and Heinze, 2000) Arabidopsisis believed to mainly contain xylan polymers consisting of a b(1,4)? linked xylose backbone, decorated with a Dglucuronic acid and/ or 4O methyl a Dglucuronic acid These residues normally oc cupy O2 positions at every 6 to 12 xylose residues The xylose backbone may also be decorated with Larabinose and/or acet ylated on C2 or C3 positions (Ebringerova and Heinze, 2000) The role of xylan in the secondary wall is not clear However, it has been suggested that xylans coat the cellulose micro?brils (Awano et al, 2002) and may in?uence the helicoidal orientation of the micro?brils (Reis and Vian, 2004) Biochemical analyses showed that several species, such as wheat ( Triticum aestivum; Porchia et al, 2002), pea ( Pisum sativum; Waldron and Brett, 1983; Baydoun et al, 1989), poplar ( Populusspp), and sycamore ( Acer pseudoplatanus ; Dalessandro and Northcote, 1981), harbor xylosyltransferase activities thought to be

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