δ12-oleate desaturase-related enzymes associated with formation of conjugated trans-δ11, cis-δ13 double bonds

Abstract

Conjugated linolenic acids are present as major seed oils in several plant species. Punicic acid (or trichosanic acid) is a conjugated linolenic acid isomer containing cis-Δ9, trans-Δ11, cis-Δ13 double bonds in the C18 carbon chain. Here we report cDNAs, TkFac and PgFac, isolated from Trichosanthes kirilowii and Punica granatum, that encode a class of conjugases associated with the formation of trans-Δ11, cis-Δ13 double bonds. Expression of TkFac and PgFac in Arabidopsis seeds under transcriptional control of the seed-specific napin promoter resulted in accumulation of punicic acid up to ∼10% (w/w) of the total seed oils. In contrast, no punicic acid was found in lipids from leaves even when the conjugases were driven under control of the cauliflower mosaic virus 35S promoter. In yeast cells grown without exogenous fatty acids in the culture medium, TkFac and PgFac expression resulted in punicic acid accumulation accompanied by 16:2Δ9cis, 12cis and 18:2Δ9, 12cis production. Thus, TkFac and PgFac are defined as bifunctional enzymes having both conjugase and Δ12-oleate desaturase activity. Furthermore, we demonstrate that 16: 2Ζ9cis, 12cis and 18:3Δ9cis, 12cis, 15cis as well as 18:2Δ9cis, 12cis are potential substrates for the conjugases to form trans-Δ11 and cis-Δ13 double bonds.