High impact information on FAD3

• Analyses of the responses to O(3) of the JA-signaling mutants jar1 and fad3/7/8 also demonstrated an antagonistic relationship between JA- and SA-signaling pathways in controlling the magnitude of O(3)-induced HR-like cell death [1].
• Corroborating evidence for this hypothesis was obtained directly by fractionation of subcellular membranes from leaf tissue and indirectly by lipid analysis of the phosphate-deprived fad3 mutant primarily deficient in extraplastidic fatty acid desaturation [2].
• These and other results indicate that the fad3 mutants are deficient in the activity of an endoplasmic reticulum 18:2 desaturase [3].
• The overall fatty compositions of leaf and root lipids from a mutant of Arabidopsis thaliana were characterized by reduced levels of linolenate (18:3) and correspondingly elevated levels of linoleate (18:2) as a consequence of a single nuclear mutation at the fad3 locus [3].
• Except for the amino-terminal domain, the deduced amino acid sequence of the fad7 gene product had high homology to the fad3 gene product, indicating that fad7 encodes an omega-3 desaturase and that the two genes arose from a common ancestral gene [4].

Biological context of FAD3

• Analysis of the fatty acid composition in the roots of Arabidopsis fad mutant and wild-type plants confirmed that the response of FAD3::LUC expression to various hormones reflected the response of endogenous FAD3 gene expression [5].
• Genomic nucleotide sequence of a gene encoding a microsomal omega-3 fatty acid desaturase from Arabidopsis thaliana [6].
• A putative desaturase cDNA clone that was isolated by low stringency heterologous probing with a cDNA for an endoplasmic reticulum-localized omega-3 desaturase (fad3) hybridized to the yeast artificial chromosomes and could not be resolved from the locus by restriction fragment length polymorphism mapping [4].
• The fatty acid phenotype was strongly expressed in root and seed tissues and this observation, together with other data, suggested that the mutation leads to increased activity of the endoplasmic reticulum 18:2 desaturase encoded by the FAD3 gene [7].
• Linkage of the mutation to fad3 raises the possibility that the lesion is an alteration to the promoter or another regulatory region of the FAD3 gene, which results in increased transcription [7].

Anatomical context of FAD3

• The Arabidopsis FAD7 gene encodes a plastid omega-3 fatty acid desaturase that catalyzes the desaturation of dienoic fatty acids to trienoic fatty acids in chloroplast membrane lipids [8].
• Using in vitro transcription/translation reactions with ER-derived microsomes, we show that both FAD2 and FAD3 are efficiently integrated into membranes by a co-translational, translocon-mediated pathway [9].

Associations of FAD3 with chemical compounds

• Mutations that impair phosphatidylcholine desaturase activity, such as fad2 and fad3, however, resulted in increased E-2-hexenal formation [10].
• We also demonstrate that while the C-terminus of FAD3 (-KSKIN) contains a functional prototypic dilysine ER retrieval motif, FAD2 contains a novel C-terminal aromatic amino acid-containing sequence (-YNNKL) that is both necessary and sufficient for maintaining localization in the ER [9].
• There are strong QTL for linoleic (18:2) and linolenic (18:3) acids contents that colocate with the FAD3 locus, another for oleic acid (18:1) that colocates with FAD2 and other less significant QTL for palmitic (16:0), stearic (18:0), and eicosaenoic (20:1) acids [11].

Other interactions of FAD3

• A putative fad8 cDNA was isolated by heterologous hybridization using a gene encoding an endoplasmic reticulum-localized omega-3 desaturase (fad3) as a probe [12].
• To investigate the biogenesis of ER-localized membrane-bound FADs, we characterized the mechanisms responsible for insertion of Arabidopsis FAD2 and Brassica FAD3 into ER membranes and determined the molecular signals that maintain their ER residency [9].
• Using mutant lines of Arabidopsis that lack the activity of the FAE1 condensing enzyme or FAD3 ER Delta-15-desaturase, we have shown that these enzymes are required for the synthesis of C20 hydroxy fatty acids and polyunsaturated hydroxy fatty acids, respectively [13].

Analytical, diagnostic and therapeutic context of FAD3

• The subcellular location of two integral membrane-bound fatty acid desaturases (Fads), Fad2 and Fad3, was elucidated by immunofluorescence microscopic analyses of tobacco suspension cells transiently transformed with different epitope-tagged versions of the enzymes [14].

References