A light‐sensitive mechanism differently regulates transcription and transcript stability of ω3 fatty‐acid desaturases (FAD3, FAD7 and FAD8) in soybean photosynthetic cell suspensions

Abstract

The x3 fatty-acid desaturases: FAD7 and FAD8 (plastid) and FAD3 (reticular) are responsible for trienoic fatty-acid (TA) production in plants. The expression of these enzymes seemed to be regulated differently in response to light. Darkness leads to a decrease in total TA level. Under such conditions, FAD3 and FAD8 transcript levels were undetectable but increased after re-illumination concomitant with TA levels, indicating a transcriptional control. On the contrary, FAD7 transcript levels were similar to illuminated control cells, suggesting the presence of a post-transcriptional control mechanism. Furthermore, FAD7 mRNA stability increased dramatically in darkness. Analysis of FAD7 protein accumulation using specific antibodies revealed that FAD7 was very stable whatever the light or darkness conditions. These results indicate that FAD7 enzyme availability is not limiting for 18:3 production in darkness. Our data point to an additional post-translational regulatory mechanism that controls the activity of FAD7 in response to light.

In Situ Molecular Identification of the Plastid ω3 Fatty Acid Desaturase FAD7 from Soybean: Evidence of Thylakoid Membrane Localization

“…We have recently described the obtention of a monospecific polyclonal antibody against the plastid v3 desaturase FAD7 from soybean (Glycine max; Collados et al, 2006). We used this antibody as a tool for immunofluorescence, immunogold labeling, and biochemical fractionation essays to precisely determine the subcellular localization of the FAD7 v3 desaturase in soybean cultured cells.…”

Blue light enhances the accumulation of eicosapentaenoic acid in a liverwort, Marchantia polymorpha L.

“…Considering the fact that the same three enzymes, D6-desaturase, D6-elongase, and D5-desaturase are involved in the synthesis of AA from LA and EPA from ALA (Kajikawa et al 2004), it is suggested that AA and EPA content were dependent on the metabolism of LA and ALA, respectively. Previous studies have reported that light induced the expression of w-3 desaturase gene which catalyzed desaturation from LA to ALA bringing into ALA increase (Collados et al 2006). However, whether expression of this gene is regulated by the light quality and intensity is not clear.…”

“…Several studies indicate that light conditions modify the composition of PUFAs. In soybean cell cultures, the relative contents of C18:2 and C18:3 fatty acids decreased in response to darkness (Collados et al 2006). In unicellular algae, illumination may induce the desaturation of fatty acids (KlyachkoGurvich et al 1999).…”

Soybean Fatty Acid Desaturation Pathway: Responses to Temperature Changes and Pathogen Infection

“…In situ analysis using confocal microscopy with FAD7 antibody and chlorophyll auto fluorescence has shown that the soybean FAD7 protein is preferentially localized to the chloroplast thylakoid membranes suggesting that not only the chloroplast envelope, but also the thylakoid membranes could be sites of lipid desaturation in higher plants (Andreu et al, 2007). GmFAD3, GmFAD7, and GmFAD8 transcription and transcript stability have been found to be differentially regulated by light (Collados et al, 2006). In soybean cell suspension, darkness leads to an overall decrease in 18:3 levels and GmFAD3 and GmFAD8 transcripts are undetectable, but after reillumination FAD3 and FAD8 transcript abundance increased concomitant with an increase in 18:3 accumulation.…”

“…Molecular identity probes (CAPS markers, SNPs) were developed for all three soybean FAD3 genes and deployment of these probes for screening combinations of FAD3 mutant alleles have allowed the development of new soybean lines with 1% 18:3 (Bilyeu et al, 2006, Beuselinck et al 2006. Chloroplast localized soybean ω-6 fatty acid desaturase genes, designated GmFAD7 and GmFAD8 (after Arabidopsis chloroplast ω-6 desaturase functional nomenclature) have been partially characterized (Collados et al, 2006) and they do possess N-terminal chloroplast signal peptides (Table 3 Table 3. Soybean (Glycine max L.) omega-3 fatty acid desaturase genes including putative chromosome and linkage group assignment, and tissue transcript expression.…”