The scientific questions addressed by my collaborators and myself are divided into different axes aimed at exploring lipid metabolism in the seed. The term metabolism refers to the de novo synthesis and utilization of fatty acids for the elaboration of complex lipids. Particular attention is paid to the biosynthesis of oils, also called triglycerides (TAGs), during seed filling.

Characterization of the chemical diversity of fatty acids stored in oilseeds, long undertaken by many groups around the world, has revealed over 400 distinct structures (Baud, 2018). The exploration of biodiversity remains incomplete and ongoing. We are deploying an innovative approach that involves analyzing separately the oil stored in the albumen and in the embryo. Often, their compositions differ, with the albumen proving to be a site of synthesis and accumulation of unusual fatty acids (Miray et al., 2021). This long-term project relies on collaborations with numerous botanical gardens around the world and partners holding oilseed collections (e.g. collections of rapeseed and camelina cultivars).

2. Enzymes of fatty acid metabolism
Although the major axes underlying lipid metabolism are relatively well characterized in seed plants, this metabolism has often been studied in model species, focusing on the major metabolites in their tissues. The core of our approach is to characterize atypical enzymes involved in the metabolism of unusual fatty acids. In the last few years, our activity has been particularly focused on the characterization of atypical plastid desaturases belonging to the acyl-ACP desaturase (AADs) family. For example, among the 7 isoforms of AADs encoded by the Arabidopsis thaliana genome, in addition to 4 archetypal, highly conserved, oleic acid (18:1 omega-9) producing ∆9 stearoyl-ACP desaturases, we were able to identify 2 atypical isoforms producing unusual omega-7 monounsaturated fatty acids (Troncoso Ponce et al., 2016; Ettaki et al., 2018). This approach allows us to identify new types of desaturases and to study the relationship between structure and function in this exceptional class of enzymes operating in a regioselective and stereospecific manner on substrates (saturated carbon chains) lacking any 'topological landmark'.

3. Regulation of lipid metabolism in the seed
The study of the transcriptional regulation of lipid metabolism in the seed corresponds to our historical activity. After extensively studying the family of AP2-like transcription factors named WRINKLED and activating the fatty acid biosynthetic pathway in different plant tissues (To et al., 2012; Marchive et al., 2014), we characterized MYB118 and MYB115, two regulators of lipid metabolism specific to the seed albumen (Barthole et al., 2014; Troncoso Ponce et al., 2016). More recently, we have identified a new clade of MYB-like transcription factors activating fatty acid biosynthesis. The specificity of these regulators compared to others already known is that they also activate the surface lipid (suberin) biosynthetic pathway (To et al., 2020). Our work is ongoing to characterize their targets and understand what distinguishes them from each other.
In parallel, we are also studying the post-translational regulations that can modulate fatty acid production in the plastid, focusing on acetyl-CoA carboxylase. We have thus contributed to demonstrate the importance of the allosteric regulator PII (Baud et al., 2010). More recently, in collaboration with the University of Missouri, we have also discovered a new family of transmembrane proteins that provide a solution to a 20 year old puzzle: why is acetyl-CoA carboxylase, which has no transmembrane domain, associated with the plastid envelope? The discovered proteins not only have an anchoring role but also regulate the activity of the enzyme and, in doing so, the production of fatty acids (Ye et al., 2020).

4. Biological functions of fatty acids in the seed
Fatty acids are used in the seed for the elaboration of different lipid pools: membrane lipids, surface lipids (suberin, cutin), reserve lipids (triacylglycerols). Through functional genomics approaches, we seek to understand the importance of the different categories of fatty acids in seed biology, from the early stages of seed development to the establishment of the young seedling just after germination.
The importance of ∆9 stearoyl-ACP desaturases (SADs) and the oleic acid (18:1 omega-9) they produce during vegetative development was known since the early 1990s. Our recent work has established that, in the seed, this enzymatic activity plays several crucial roles that had previously gone unnoticed because of the partial functional redundancy of four SAD-like isoforms present in this organ. It was the assembly and fine characterization of a collection of 30 single and multiple mutants that showed the extent to which oleic acid production plays not one but several prominent roles throughout seed development, from the first cell divisions of the main zygote to seed filling during the maturation phase (Kazaz et al., 2020).

I would like to conclude by expressing my immense gratitude to all the past collaborators of the team whose enthusiastic involvement has allowed this research to come alive:  

- BARTHOLE Guillaume, Master (2010) and Thesis (2010-2013)
- CHALVIN Camille, Bachelor's degree (2012)
- CUZZI Delphine, Engineer (2009-2010)
- ETTAKI Hasna, Master (2017)
- HARSCOET Erwana, Technician (2008-2009)
- KAZAZ Sami, Master (2018) and Thesis (2018-2021)
- MARCHIVE Chloé, Post-doctoral fellow (2011-2014)
- MIRAY Romane, Master (2020) and Thesis (2020-2023)
- MOULIN Solène, Bachelor's degree (2012)
- NIKOVICS Krisztina, Post-doctoral fellow (2013-2014)
- RATAHIRY Sarah, Master (2023)
- ROCHAT Christine, Researcher (2001-2006)
- SCAGNELLI Aurélie, Engineer (2010)
- THUEUX Jean, Master (2019)
- TREMBLAIS Geoffrey, Master (2016)
- TRONCOSO PONCE Adrian, Post-doctoral fellow (2014-2016)
- VASSELON Damien, Engineer (2017-2018)
- WILCH Antonia, Master (2014)
- WUILLEME Sylvie, Technician (2001-2006)
- YUNG William, Master (2013)  

If you wish to join us, do not hesitate to contact us!