Free Fatty Acids Regulate Two Galactosyltransferases in Chloroplast Envelope Membranes Isolated from Spinach Leaves

Sakaki, Takeshi; Kondo, Noriaki; Yamada, Mitsuhiro

doi:10.1104/pp.94.2.781

Cited by 28 publications

(12 citation statements)

References 27 publications

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“…Previous studies have demonstrated activation of TAG synthesis and a concurrent decrease in galactolipids and phospholipid in ozone-fumigated leaves (Sakaki et al, 1990a(Sakaki et al, , 1990b(Sakaki et al, , 1990c. Drought-stressed cotton leaves similarly exhibit a significant decline in polar lipid and a parallel increase in TAG (El-Hafid et al, 1989).…”

Section: Discussionmentioning

confidence: 99%

A Role for Diacylglycerol Acyltransferase during Leaf Senescence

2002

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Lipid analysis of rosette leaves from Arabidopsis has revealed an accumulation of triacylglycerol (TAG) with advancing leaf senescence coincident with an increase in the abundance and size of plastoglobuli. The terminal step in the biosynthesis of TAG in Arabidopsis is catalyzed by diacylglycerol acyltransferase 1 (DGAT1; EC 2.3.1.20). When gel blots of RNA isolated from rosette leaves at various stages of development were probed with the Arabidopsis expressed sequence tag clone, E6B2T7, which has been annotated as DGAT1, a steep increase in DGAT1 transcript levels was evident in the senescing leaves coincident with the accumulation of TAG. The increase in DGAT1 transcript correlated temporally with enhanced levels of DGAT1 protein detected immunologically. Two lines of evidence indicated that the TAG of senescing leaves is synthesized in chloroplasts and sequesters fatty acids released from the catabolism of thylakoid galactolipids. First, TAG isolated from senescing leaves proved to be enriched in hexadecatrienoic acid (16:3) and linolenic acid (18:3), which are normally present in thylakoid galactolipids. Second, DGAT1 protein in senescing leaves was found to be associated with chloroplast membranes. These findings collectively indicate that diacylglycerol acyltransferase plays a role in senescence by sequestering fatty acids de-esterified from galactolipids into TAG. This would appear to be an intermediate step in the conversion of thylakoid fatty acids to phloem-mobile sucrose during leaf senescence.Diacylglycerol (DAG) acyltransferase (DGAT; EC 2.3.1.20) mediates the final acylation step in the synthesis of triacylglycerol (TAG). It is present in most plant organs, including leaves, petals, fruits, anthers, and developing seeds (Hobbs et al., 1999). In seeds, TAG is thought to be synthesized within the membranes of the endoplasmic reticulum and subsequently released into the cytosol in the form of oil bodies, which bleb from the cytoplasmic surface of the endoplasmic reticulum (Huang, 1992). The stored TAG is localized in the interior of the oil body, and the surfaces of oil bodies are coated with a monolayer of phospholipid associated with oleosin, the major protein of oil bodies. The acyl chains of the phospholipid monolayer are embedded in the TAG interior of the oil body. Oleosin is a structural protein that is thought to prevent coalescence of oil bodies during seed dehydration (Huang, 1996). That oil bodies originate from the endoplasmic reticulum is consistent with the finding that enzymes of TAG synthesis, including DGAT, are present in microsomal membrane fractions, which are known to contain vesicles of endoplasmic reticulum (Kwanyuen and Wilson, 1986). In addition, TAG can be synthesized in vitro in the presence of microsomes isolated from developing seeds (Lacey et al., 1999).Although TAG formation in seeds is believed to occur in the ER, there have been several reports indicating that purified chloroplast envelope membranes from leaves are also capable of synthesizing this storage lipid (Siebe...

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Section: Discussionmentioning

confidence: 99%

A Role for Diacylglycerol Acyltransferase during Leaf Senescence

2002

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“…These authors postulated that GGGT provides the DAG precursor for triacylglycerol biosynthesis following ozone fumigation and produces oligogalactolipids in the process. Moreover, it was shown that GGGT was activated by free fatty acids in the presence of divalent cations such as Mg 2ϩ following ozone fumigation, whereas UDP-Gal-dependent galactosyltransferases were inhibited by free fatty acids under these conditions (51). Therefore one can speculate that GGGT plays a role during ozone-induced injury (Fig.…”

Section: Minireview: Plant Galactoglycerolipid Biosynthesis 2399mentioning

confidence: 99%

Three Enzyme Systems for Galactoglycerolipid Biosynthesis Are Coordinately Regulated in Plants

Benning

Ohta

2005

Journal of Biological Chemistry

195

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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“…Transgenic plants were clearly under stress throughout growth and development as indicated by the consistent presence of anthocyanin in the leaves. Previous studies have demonstrated activation of TAG synthesis and a concurrent decrease in galactolipids in ozone-fumigated leaves (Sakaki et al, 1990a(Sakaki et al, , 1990b(Sakaki et al, , 1990c. Activation of TAG synthesis in the ozone-treated leaves is thought to reflect sequestration of fatty acids deesterified from galactolipids in response to ozone stress, which would otherwise disrupt the structure of thylakoid membranes (Sakaki et al, 1990b).…”

Section: [Liv]-x-[livafy]-[liamvst]-g-[hywv]-s-x-g-[gstac]mentioning

confidence: 99%

Characterization of a Plastid Triacylglycerol Lipase from Arabidopsis

et al. 2007

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Full-length cDNA corresponding to Arabidopsis (Arabidopsis thaliana) gene At2g31690, which has been annotated in GenBank as a putative triacylglycerol (TAG) lipase, was obtained by reverse transcription-polymerase chain reaction using RNA from senescing rosette leaves of Arabidopsis as a template. The cognate protein was found to contain the lipase active site sequence, and corresponding recombinant protein proved capable of deesterifying TAG. In vitro chloroplast import assays indicated that the lipase is targeted to chloroplasts. This was confirmed by confocal microscopy of rosette leaf tissue treated with fluorescein isocyanate-labeled, lipase-specific antibody, which revealed that lipase protein colocalizes with plastoglobular neutral lipids. Western-blot analysis indicated that the lipase is expressed in roots, inflorescence stems, flowers, siliques, and leaves and that it is strongly up-regulated in senescing rosette leaf tissue. Transgenic plants with suppressed lipase protein levels were obtained by expressing At2g31690 cDNA in antisense orientation under the regulation of a constitutive promoter. Transgenic plants bolted and flowered at the same time as wild-type plants, but were severely stunted and exhibited delayed rosette senescence. Moreover, the stunted growth phenotype correlated with irregular chloroplast morphology. The chloroplasts of transgenic plants were structurally deformed, had reduced abundance of thylakoids that were abnormally stacked, and contained more plastoglobular neutral lipids than chloroplasts of wild-type plants. These observations collectively indicate that this TAG lipase plays a role in maintaining the structural integrity of chloroplasts, possibly by mobilizing the fatty acids of plastoglobular TAG.

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Free Fatty Acids Regulate Two Galactosyltransferases in Chloroplast Envelope Membranes Isolated from Spinach Leaves

Cited by 28 publications

References 27 publications

A Role for Diacylglycerol Acyltransferase during Leaf Senescence

A Role for Diacylglycerol Acyltransferase during Leaf Senescence

Three Enzyme Systems for Galactoglycerolipid Biosynthesis Are Coordinately Regulated in Plants

Characterization of a Plastid Triacylglycerol Lipase from Arabidopsis

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