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Plastidic Δ6 fatty-acid desaturases with distinctive substrate specificity regulate the pool of c18-pufas in the ancestral picoalga ostreococcus tauri

Abstract : Eukaryotic Δ6-desaturases are microsomal enzymes which balance the synthesis of ω-3 and ω-6 C18-polyunsaturated-fatty-acids (PUFA) accordingly to their specificity. In several microalgae, including O. tauri , plastidic C18-PUFA are specifically regulated by environmental cues suggesting an autonomous control of Δ6-desaturation of plastidic PUFA. Sequence retrieval from O. tauri desaturases, highlighted two putative Δ6/Δ8-desaturases sequences clustering, with other microalgal homologs, apart from other characterized Δ-6 desaturases. Their overexpression in heterologous hosts, including N. benthamiana and Synechocystis , unveiled their Δ6-desaturation activity and plastid localization. O. tauri lines overexpressing these Δ6-desaturases no longer adjusted their plastidic C18-PUFA amount under phosphate starvation but didn’t show any obvious physiological alterations. Detailed lipid analyses from the various overexpressing hosts, unravelled that the substrate features involved in the Δ6-desaturase specificity importantly involved the lipid head-group and likely the non-substrate acyl-chain, in addition to the overall preference for the ω-class of the substrate acyl-chain. The most active desaturase displayed a broad range substrate specificity for plastidic lipids and a preference for ω-3 substrates, while the other was selective for ω-6 substrates, phosphatidylglycerol and 16:4-galactolipid species specific to the native host. The distribution of plastidial Δ6-desaturase products in eukaryotic hosts suggested the occurrence of C18-PUFA export from the plastid. One sentence summary Osteococcus tauri plastidic lipid C18-PUFA remodelling involves two plastid-located cytochrome-b5 fused Δ6-desaturases with distinct preferences for both head-group and acyl-chain.
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Preprints, Working Papers, ...
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https://hal.inrae.fr/hal-03333546
Contributor : Soizic Morin <>
Submitted on : Friday, September 3, 2021 - 9:39:49 AM
Last modification on : Tuesday, September 7, 2021 - 3:44:22 PM

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Charlotte Degraeve-Guilbault C., Rodrigo Gomez, Cécile. Lemoigne, Nattiwong Pankansem, Soizic Morin, et al.. Plastidic Δ6 fatty-acid desaturases with distinctive substrate specificity regulate the pool of c18-pufas in the ancestral picoalga ostreococcus tauri. 2021. ⟨hal-03333546⟩

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