Biosynthesis of Digalactosyldiacylglycerol in Plastids from 16:3 and 18:3 Plants

Heemskerk, Johan W. M.; Storz, Thomas; Schmidt, Richard R.; Heinz, Ernst

doi:10.1104/pp.93.4.1286

Cited by 62 publications

(37 citation statements)

References 29 publications

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“…The recombinant DGD2 protein uses UDP-Gal as the galactose donor and MGDG as the acceptor (26). MGDG in the absence of UDP-Gal did not lead to the formation of DGDG ruling out a GGGT activity originally proposed to be the major DGDG synthase activity in plants (21)(22)(23). By deleting the N-terminal domain it was recently demonstrated that the glycosyltransferase domain of DGD1 also utilizes UDP-Gal as the galactose donor (28).…”

Section: Digalactosyldiacylglycerol Synthasesmentioning

confidence: 99%

Three Enzyme Systems for Galactoglycerolipid Biosynthesis Are Coordinately Regulated in Plants

Benning

Ohta

2005

Journal of Biological Chemistry

193

148

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Galactoglycerolipids, in which galactose is bound at the glycerol sn-3 position in O-glycosidic linkage to diacylglycerol, are abundant in plants and photosynthetic bacteria, where they constitute the bulk of the polar lipids of the photosynthetic membranes. Galactoglycerolipid biosynthesis in plants is highly compartmentalized involving enzymes at the endoplasmic reticulum and the two chloroplast envelopes. This peculiar organization requires extensive trafficking of lipid precursors. It is now increasingly apparent that there are three different sets of lipid galactosyltransferases capable of galactoglycerolipid biosynthesis in the model plant Arabidopsis. Two enzymes, MGD1 and DGD1, provide the bulk of galactoglycerolipids in the chloroplast and in photosynthetic tissues in general. Under phosphate-limited growth conditions and in non-photosynthetic tissues MGD2/3 and DGD2 are highly active. Moreover, galactoglycerolipids produced by this second pathway are often found in extraplastidic membranes. Although these galactosyltransferases use UDP-Gal as the galactose donor, a third pathway involves a processive enzyme, which transfers galactose from one galactolipid to another.In thinking about membrane lipids, phosphoglycerolipids often come to mind first as these are the primary building blocks of many eukaryotic and prokaryotic cell membranes. However, in plant cells the fraction of phosphoglycerolipids is relatively small. Instead, non-phosphorous galactoglycerolipids are predominant, representing up to 50% of polar lipids in extracts of photosynthetic tissues (1). Of the different galactolipids reported for plants (2), most abundant are the monogalactosyldiacylglycerol (MGDG) 1 and digalactosyldiacylglycerol (DGDG) lipids (cf. Fig. 1 for structures). In addition, under certain circumstances, e.g. in the Arabidopsis tgd1 mutant (3), plants can synthesize higher galactosylated forms of galactoglycerolipids. Although most of these lipids are restricted to the chloroplast membranes in plants, it has become increasingly apparent that galactoglycerolipids are present in extraplastidic membranes in non-photosynthetic tissues or under phosphate-limited growth conditions (4). Current evidence suggests that galactoglycerolipids are exclusively synthesized by enzymes associated with the two chloroplast envelopes in plants, a fact that requires the transfer of lipid precursors to, between, and through the envelopes as well as that of galactoglycerolipids from the envelopes to the photosynthetic membranes inside the chloroplast (thylakoids) and to extraplastidic membranes (5). The three classes of glycosyltransferases ( Fig. 1) involved in galactoglycerolipid biosynthesis in plants and their respective functions and interactions in vivo will be discussed. Monogalactosyldiacylglycerol SynthasesThe most abundant plant galactoglycerolipid, 1␤-MGDG, is synthesized in plants by the action of a galactosyltransferase (MGDG synthase, EC 2.4.1.46) catalyzing the transfer of a galactosyl residue from UDP-1␣-Gal to the sn-3-posit...

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Section: Digalactosyldiacylglycerol Synthasesmentioning

confidence: 99%

Three Enzyme Systems for Galactoglycerolipid Biosynthesis Are Coordinately Regulated in Plants

Benning

Ohta

2005

Journal of Biological Chemistry

193

148

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“…Van Besouw and Wintermans [55], Heemskerk and Wintermans [56] and Heemskerk et al [57] have proposed that the galactolipid :galactolipid galactosyltransferase is indeed responsible for digalactosyldiacylglycerol synthesis. For instance, Heemskerk et al [57] analyzed galactolipid synthesis in chloroplasts or chromoplasts from eight species of 16:3 and 18:3 plants and found that digalactosyldiacylglycerol formation is never stimulated by UDP-Gal or any other nucleoside 5'-diphosphodigalactoside ; in all cases, digalactosyldiacylglycerol formation was reduced by thermolysin digestion of intact organelles. In vitro, the galactolipid :galactolipid galactosyltransferase does not show strong specificity for any monogalactosyldiacylglycerol molecular species.…”

Section: Biosynthesis Of Other Plastid Glycerolipids (Digalactosyldiamentioning

confidence: 99%

Molecular aspects of plastid envelope biochemistry

Joyard

Block

Douce

1991

European Journal of Biochemistry

118

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“…6A). Galactolipid:galactolipid galactosyltransferase is known to form DGDG by the transfer of a galactosyl group from one MGDG to another MGDG molecule (10,12). Its activity in spinach chloroplasts is inhibited by treatment of chloroplasts with the nonpenetrating proteinase thermolysin (10).…”

Section: Formation and Desaturation Of Prokaryotic Galactolipids In Smentioning

confidence: 99%

“…(c) Eukaryotic MGDG and DGDG are synthesized at similar rates. (d) Only two galactosyltransferases are known which synthesize galactolipids (10)(11)(12). (e) In vitro, either galactosyltransferase discriminates only moderately between various molecular species ofMGDG or DGDG, but polyenoic MGDG is galactosylated faster than oligoenoic MGDG(l1).…”

Section: Regulation Of Galactolipid Synthesis In Spinach Leavesmentioning

confidence: 99%

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Biosynthesis and Desaturation of Prokaryotic Galactolipids in Leaves and Isolated Chloroplasts from Spinach

Heemskerk¹,

Schmidt²,

Hammer³

et al. 1991

Plant Physiol.

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Mono-and digalactosyldiacylglycerol (MGDG and DGDG) were isolated from the leaves of sixteen 16:3 plants. In all of these plant species, the sn-2 position of MGDG was more enriched in C1, fatty acids than sn-2 of DGDG. The molar ratios of prokaryotic MGDG to prokaryotic DGDG ranged from 4 to 10. This suggests that 16:3 plants synthesize more prokaryotic MGDG than prokaryotic DGDG. In the 16:3 plant Spinacia oleracea L. (spinach), the formation of prokaryotic galactolipids was studied both in vivo and in vitro. In intact spinach leaves as well as in chloroplasts isolated from these leaves, radioactivity from [1-14C]acetate accumulated 10 times faster in MGDG than in DGDG. After 2 hours of incorporation, most labeled galactolipids from leaves and all labeled galactolipids from isolated chloroplasts were in the prokaryotic configuration. Both in vivo and in vitro, the desaturation of labeled palmitate and oleate to trienoic fatty acids was higher in MGDG than in DGDG. In leaves, palmitate at the sn-2 position was desaturated in MGDG but not in DGDG. In isolated chloroplasts, palmitate at sn-2 similarly was desaturated only in MGDG, but palmitate and oleate at the sn-I position were desaturated in MGDG as well as in DGDG. Apparently, palmitate desaturase reacts with sn-1 palmitate in either galactolipid, but does not react with the sn-2 fatty acid of DGDG. These results demonstrate that isolated spinach chloroplasts can synthesize and desaturate prokaryotic MGDG and DGDG. The finally accumulating molecular species, MGDG(18:3/16:3) and DGDG(18:3/16:0), are made by the chloroplasts in proportions similar to those found in leaves. Biosynthesis of prokaryotic MGDG and DGDG has been measured in vivo by the labeling of leaves from 16:3 plants with ['4C]acetate (4, 26, 29). In de novo-made MGDG, both C16 and C18 fatty acids were labeled and both were gradually desaturated to trienoic fatty acids. Desaturation of newly made DGDG, however, was limited to its labeled C18 fatty acids, suggesting a different action of the desaturases on MGDG and DGDG. Strong evidence that desaturation of MGDG fatty acids, indeed, proceeds as a lipid-linked process has been provided by Sato et al. (25) for the blue-green alga Anabaena variabilis.Following the initial study of galactolipid desaturation in vitro by Roughan et al. (22), it was confirmed recently that isolated spinach chloroplasts convert de novo-made MGDG(18:1/16:0) to ultimately MGDG(18:3/16:3) (1,15). In the present paper, we extend this work and report for the first time the synthesis of prokaryotic DGDG(18:1/16:0) and its subsequent desaturation in isolated chloroplasts. The rates observed were low, but are consistent with the small proportions of prokaryotic DGDG that were found in the leaves of sixteen 16:3 plants. A scheme is proposed for the regulation and interdependence of galactolipid synthesis in 16:3 plants, which tries to explain the typical differences in content and fatty acid composition between the major molecular species of MGDG and DGDG. 3Abbreviat...

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Biosynthesis of Digalactosyldiacylglycerol in Plastids from 16:3 and 18:3 Plants

Cited by 62 publications

References 29 publications

Three Enzyme Systems for Galactoglycerolipid Biosynthesis Are Coordinately Regulated in Plants

Three Enzyme Systems for Galactoglycerolipid Biosynthesis Are Coordinately Regulated in Plants

Molecular aspects of plastid envelope biochemistry

Biosynthesis and Desaturation of Prokaryotic Galactolipids in Leaves and Isolated Chloroplasts from Spinach

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