Final Report Summary - BIOLIPOL (Unraveling the biosynthesis of fatty acid-based lipid polymers in plants) Project context and objectivesThe aim of this project was to identify new enzymes involved in the biosynthesis of the plant protective lipid polyesters cutin and suberin, and gain insights into the acyl oxidation and acyltransfer reactions of the pathway.Work performedTwenty-one candidate genes have been tested by reverse genetics in the model plant Arabidopsis thaliana. Mutants for four candidate genes have been found to be essential for cutin synthesis and were characterised in detail. A major result was the discovery that the in-chain hydroxylase synthesizing 10,16-dihydroxypalmitate (a common cutin monomer in nature) was encoded by CYP77A6, a member of a P450 family with no previously ascribed in vivo function. It was demonstrated that CYP77A6 acts after the terminal hydroxylase CYP86A4 to produce 10,16-dihydroxypalmitate. Analysis of the mutants has also shown that the cutin polymer is central to the formation of petal nanoridges (Li-Beisson et al. 2009 PNAS 106:22008). In addition, it has been demonstrated that CYP77A4 is involved specifically in the synthesis of a trihydroxy acid found in cutins and is essential for seed germination under osmotic stress (PhD thesis of G. Verdier, 2010-2013, Aix-Marseille University).Gene overexpression studies have also been conducted in Arabidopsis and yeast. Several combinations of GPAT acyltransferases and fatty acid oxidases have been overexpressed. The combination GPAT5/CYP86B1 has allowed the production and secretion of very long chain hydroxyacids and diacids that are normally found in the suberin of roots.Main resultsThe project has yielded important new insights into the identity and characteristics of the enzymes involved in the pathway of plant lipid polyester biosynthesis. The enzymes identified are potentially useful for biotechnological applications such as:- improving barrier functions in crops by genetically engineering the cutin polymer (resistance to pathogens, desiccation and/or salinity);- producing high amounts of oxidised fatty acids (omega-hydroxy fatty acids, fatty diols, dicarboxylic acids) in plants, which could replace petroleum-derived products for the synthesis of polymers and specialty chemicals.
