Proteomic identification of lipid-bodies-associated proteins in maize seeds

Seeds store lipids in the form of lipid bodies (LBs) for germination and early seedling growth. LBs can be easily isolated by the established floating-extraction method from oleaginous seeds containing a large quantity of LBs. Compared to oleaginous seeds, maize and other cereal seeds contain a small quantity of LBs, so it is difficult to isolate a sufficient quantity of LBs from their embryos for 2DE-based proteomic analysis. At present, only a limited number of LBs-associated proteins in maize embryos have been identified. We here reported a modified floating-extraction method using polyvinylidene difluoride disc to collect floating LBs from maize embryo extracts. The LBs-associated proteins were resolved with two-dimensional electrophoresis and identified with mass spectrometry. As a result, several well-known LBs proteins were identified in the purified LBs fraction, such as oleosin, caleosin, and steroleosin. We also identified another two LBs proteins, corticosteroid 11-β-dehydrogenase 1 and 11-β-hydroxysteroid dehydrogenase-like 5. In particular, steroleosin, corticosteroid 11-β-dehydrogenase 1, 11-β-hydroxysteroid dehydrogenase-like, and hydroxyproline-rich glycoprotein were found as the most abundant protein components in maize LBs. The data set of maize LBs subproteome would provide insights into functional research of LBs-associated proteins during seed development and germination. Additionally, the protocol developed here is expected to be applicable for isolating LBs in other seeds or tissues containing a low quantity of LBs.