Presentation Title

Methylated Sugar Residues in Arabinogalactan-Proteins of the Moss Physcomitrella patens

Start Date

November 2016

End Date

November 2016

Location

HUB 302-#5

Type of Presentation

Poster

Abstract

Exploitation of evolutionary succession in plants has the potential to improve agriculture, production of medicinal drugs, and sustainable biofuels. Arabinogalactan-proteins (AGPs) are proteoglycans found in the cell walls and plasma membranes of plants from the relictual Bryophytes to the most derived gymnosperms and angiosperms. AGPs in the moss Physcomitrella patens (a Bryophyte) are generally structurally similar to AGPs in highly derived angiosperms, except moss AGPs contain methylated ethers on certain carbon atoms in certain carbohydrate residues. Little is known of the function of methylated sugars. Biosynthesis of methylated carbohydrates is catalyzed by a methyltransferase enzyme acting on two substrates: a methyl donor (most commonly S-adenosylmethionine) and the hydroxyl group of a carbohydrate. Biochemical purification and analysis has previously revealed that AGPs in Physcomitrella contain up to 15 mol% of 3-O-methyl-L-rhamnosyl (3-O-Me-Rha) residues, an unusual carbohydrate not found in angiosperm AGPs. A moss gene encoding a methyltransferase that makes 3-O-Me-Rha residues has yet to be found, but two moss genes have been found to encode methyltransferases MT1 and MT6 that, when transgenically expressed in tobacco, cause synthesis of 3-O-methyl-D-galactosyl (3-O-Me-Gal) residues in the cell wall. Curiously, few if any 3-O-Me-Gal residues are found in the leafy gametophyte of Physcomitrella. The first goal of the present project was to determine whether 3-O-Me-Gal residues are present during the protonemal stage of the Physcomitrella life cycle. Analysis of Physcomitrella cell walls by cleavage of glycosidic bonds, derivatization, and gas chromatography-mass spectrometry showed that 3-O-Me-Gal residues are no more abundant in the cell walls of protonema than in the cell walls of leafy gametophyte. To further investigate this curious situation, the next goal of this project is to generate mt1 and mt6 knockout mutants of Physcomitrella.

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Nov 12th, 4:00 PM Nov 12th, 5:00 PM

Methylated Sugar Residues in Arabinogalactan-Proteins of the Moss Physcomitrella patens

HUB 302-#5

Exploitation of evolutionary succession in plants has the potential to improve agriculture, production of medicinal drugs, and sustainable biofuels. Arabinogalactan-proteins (AGPs) are proteoglycans found in the cell walls and plasma membranes of plants from the relictual Bryophytes to the most derived gymnosperms and angiosperms. AGPs in the moss Physcomitrella patens (a Bryophyte) are generally structurally similar to AGPs in highly derived angiosperms, except moss AGPs contain methylated ethers on certain carbon atoms in certain carbohydrate residues. Little is known of the function of methylated sugars. Biosynthesis of methylated carbohydrates is catalyzed by a methyltransferase enzyme acting on two substrates: a methyl donor (most commonly S-adenosylmethionine) and the hydroxyl group of a carbohydrate. Biochemical purification and analysis has previously revealed that AGPs in Physcomitrella contain up to 15 mol% of 3-O-methyl-L-rhamnosyl (3-O-Me-Rha) residues, an unusual carbohydrate not found in angiosperm AGPs. A moss gene encoding a methyltransferase that makes 3-O-Me-Rha residues has yet to be found, but two moss genes have been found to encode methyltransferases MT1 and MT6 that, when transgenically expressed in tobacco, cause synthesis of 3-O-methyl-D-galactosyl (3-O-Me-Gal) residues in the cell wall. Curiously, few if any 3-O-Me-Gal residues are found in the leafy gametophyte of Physcomitrella. The first goal of the present project was to determine whether 3-O-Me-Gal residues are present during the protonemal stage of the Physcomitrella life cycle. Analysis of Physcomitrella cell walls by cleavage of glycosidic bonds, derivatization, and gas chromatography-mass spectrometry showed that 3-O-Me-Gal residues are no more abundant in the cell walls of protonema than in the cell walls of leafy gametophyte. To further investigate this curious situation, the next goal of this project is to generate mt1 and mt6 knockout mutants of Physcomitrella.