FATTY ACID DESATURASE4 of Arabidopsis encodes a protein distinct from characterized fatty acid desaturases

Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, USA.
The Plant Journal (Impact Factor: 5.97). 09/2009; 60(5):832-9. DOI: 10.1111/j.1365-313X.2009.04001.x
Source: PubMed


Polar membrane glycerolipids occur in a mixture of molecular species defined by a polar head group and characteristic acyl groups esterified to a glycerol backbone. A molecular species of phosphatidylglycerol specific to chloroplasts of plants carries a Delta(3-trans) hexadecenoic acid in the sn-2 position of its core glyceryl moiety. The fad4-1 mutant of Arabidopsis thaliana missing this particular phosphatidylglycerol molecular species lacks the necessary fatty acid desaturase, or a component thereof. The overwhelming majority of acyl groups associated with membrane lipids in plants contains double bonds with a cis configuration. However, FAD4 is unusual because it is involved in the formation of a trans double bond introduced close to the carboxyl group of palmitic acid, which is specifically esterified to the sn-2 glyceryl carbon of phosphatidylglycerol. As a first step towards the analysis of this unusual desaturase reaction, the FAD4 gene was identified by mapping of the FAD4 locus and coexpression analysis with known lipid genes. FAD4 encodes a predicted integral membrane protein that appears to be unrelated to classic membrane bound fatty acid desaturases based on overall sequence conservation. However, the FAD4 protein contains two histidine motifs resembling those of metalloproteins such as fatty acid desaturases. FAD4 is targeted to the plastid. Overexpression of the cDNA in transgenic Arabidopsis led to increased accumulation of the Delta(3-trans) hexadecanoyl group in phosphatidylglycerol relative to wild type. Taken together these results are consistent with the hypothesis that FAD4 is the founding member of a novel class of fatty acid desaturases.

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    • " - ase ( D9 - desaturase ) is the only soluble enzyme that introduces a double bond to the D9 position of C18 : 0 - ACP to form C18 : 1 - ACP , whereas other desaturases are membrane proteins that desaturate the acyl - groups of lipid molecules ( Browse et al . , 1989 , 1985 ; Iba et al . , 1993 ; Heilmann et al . , 2004 ; Kachroo et al . , 2007 ; Gao et al . , 2009 ) . In plastids , the D9 - desaturase – catalyzed desaturation reaction uses reduced ferredoxin as the electron donor and molecular oxygen as one of the substrates ( Schultz et al . , 2000 ) . In IMET1 , the transcript level of one pu - tative soluble D9 - desaturase ( g481 ) increased immediately upon the onset of N deprivation and rem"
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    • "The transcription of FAD3 appeared 8-fold and that of SAD6 25-fold higher (Fig. 2, A and C). In contrast, FAD4, encoding a desaturase known to generate D 3 -trans-hexadecenoic acid (Gao et al., 2009), was almost 4-fold down-regulated. The expression of all other genes of the two desaturase families was either reduced or remained unchanged. "
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    • "However, this reduction does not reflect a general downregulation of prokaryotic PG synthesis, but rather a decreased degree of desaturation of 16:0 at the sn2 position (Figure 8). Thus, the alteration in PG species in the cds1cds2 mutant can be explained by reduced FAD4 activity (Gao et al., 2009) (Figures 7 and 8). Unlike PG, PI is exclusively synthesized at the ER (L€ ofke et al., 2008). "
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