Characterization of germination-specific lipid transfer proteins from Euphorbia lagascae

The endosperm of Euphorbia lagascae Spreng. seeds contains high levels of the epoxidated fatty acid vernolic acid ( cis-12-epoxyoctadeca-cis-9-enoic acid). To obtain transgenic oilcrops producing high levels of vernolic acid, better knowledge of its endogenous metabolism is needed. In this paper we study the gene activities involved in the mobilization and oxidation of vernolic acid during germination. A cDNA library was constructed from mRNA isolated from germinating E. lagascae seeds. Over 300 cDNA clones were partially characterized by DNA sequencing. Of the sequenced cDNAs, 18% encoded proteins with a putative function related to the metabolism of lipids or fatty acids. Among these cDNAs were genes coding for lipase, thiolase, acyl-CoA reductase and epoxide hydrolase. Of the sequenced clones, 4.5% encoded lipid-transfer proteins (LTPs), indicating the high abundance of such proteins during germination. We isolated the full-length sequences of the E. lagascae cDNAs encoding the LTPs ElLTP1 and ElLTP2. These proteins share only 38% identity, but both show high similarity to LTPs from other plant species. Both sequences contain eight cysteine residues, which are conserved in most plant LTPs. Expression analysis revealed that both genes were specifically expressed during germination.