Abstract
Sunflower seeds (Helianthus annuus L.) accumulate large quantities of triacylglycerols (TAG) between 12 and 28 days after flowering (DAF). This is the period of maximal acyl-acyl carrier protein (acyl-ACP) thioesterase activity in vitro, the enzymes that terminate the process of de novo fatty acid synthesis by catalyzing the hydrolysis of the acyl-ACPs synthesized by fatty acid synthase. Fatty acid thioesterases can be classified into two families with distinct substrate specificities, namely FatA and FatB. Here, some new aspects of these enzymes have been studied, assessing how both enzymes contribute to the acyl composition of sunflower oil, not least through the changes in their expression during the process of seed filling. Moreover, the binding pockets of these enzymes were modeled based on new data from plant thioesterases, revealing important differences in their volume and geometry. Finally, the subcellular location of the two enzymes was evaluated and while both possess an N-terminal plastid transit peptide, only in FatB contains a hydrophobic sequence that could potentially serve as a transmembrane domain. Indeed, using in vivo imaging and organelle fractionation, H. annuus thioesterases, HaFatA and HaFatB, appear to be differentially localized in the plastid stroma and membrane envelope, respectively. The divergent roles fulfilled by HaFatA and HaFatB in oil biosynthesis are discussed in the light of our data.
Highlights
In higher plants, de novo synthesized fatty acids can be used to produce glycerolipids in the plastid through the activity of plastidial acyltransferases
We assessed the subcellular localization of both sunflower thioesterases in transiently transformed tobacco suspension-cultured cells via confocal laser-scanning microscopy (CLSM). We show that both HaFatA and HaFatB localized to the plastid stroma, HaFATB localized to the plastid inner envelope membrane when co-expressed with an inner membrane marker protein
We examined whether removal of the hydrophobic sequence from HaFATB influenced its subplastidial localization in BY-2 cells
Summary
De novo synthesized fatty acids can be used to produce glycerolipids in the plastid through the activity of plastidial acyltransferases (prokaryotic pathway: Li-Beisson et al, 2010). FatB2 enzymes are widely distributed among plant species, and they display specificity toward palmitoyl- and stearoyl-ACPs when assayed with their physiological acyl-ACP substrates (Dörmann et al, 2000; Salas and Ohlrogge, 2002; Aznar-Moreno et al, 2016) The role of these enzymes in correct plant development has been demonstrated by reverse genetics (Bonaventure et al, 2003), and they are probably involved in supplying the saturated fatty acids necessary for the synthesis of distinct essential metabolites, such as sphingolipid long chain bases (Chen et al, 2008). This feature indicates that these enzymes probably differ in their location as well as their substrate specificity, this has not as yet been supported by specific data regarding their subcellular locations
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
