Lipid droplets proteome reveals dynamic changes of lipid droplets protein during embryonic development of Carya cathayensis nuts.

Lipid droplets (LD) is an important intracellular organelle for triacylglycerols (TAGs) storage. A variety of proteins on the surface of LD coordinately control the contents, size, stability and biogenesis of LD. However, the LD proteins in Chinese hickory (Carya cathayensis) nuts, which is rich in oil and composed of unsaturated fatty acids, have not been identified and their roles in LD formation still remain largely unknown. In present study, LD fractions from three developmental stages of Chinese hickory seed were enriched and the LD fraction accumulated proteins were then isolated and analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Protein compositions throughout the various developmental phases were calculated using label-free intensity-based absolute quantification (iBAQ) algorithm. The dynamic proportion of high abundance lipid droplets proteins such as oleosins 2 (OLE2), caleosins 1 (CLO1) and steroleosin 5 (HSD5) increased parallelly with the embryo development. For low abundance lipid droplets proteins, seed LD protein 2 (SLDP2), sterol methyltransferase 1 (SMT1) and LD-associated protein 1 (LDAP1) were the predominant proteins. Moreover, 14 low abundance OB proteins such as oil body-associated protein 2 A (OBAP2A) were selected for future investigation that may associate with embryo development. Overall, 62 differentially expressed proteins (DEPs) were determined by label free quantification (LFQ) algorithms and may involve in LD biogenesis. Furthermore, the subcellular localization validation indicated that selected LD proteins were targeted to the lipid droplets, confirming the promising of proteome data. Taken together, this comparative study may shed light on further study to understand the lipid droplets function in the seed, which contains high oil content.