Characterization of diacylglycerol acyltransferase 2 from Idesia polycarpa and function analysis.

Idesia polycarpa is an oil-producing tree native to China and Northeast Asia. The fruits of I. polycarpa which are named oil grape are unique in that they contain large amounts saturated and unsaturated lipids. Diacylglycerol acyltransferase 2 (DGAT2) is a key enzyme catalyzing the final step of triacylglyceride (TAG) synthesis. However, expression and bioinformatics of DGAT2 in I. polycarpa are still blank. In order to further understand the lipogenesis of oil grape, we contrasted seven various growth periods fruits from seed formation to seed maturation. Lipid accumulation rates and final lipid content were significantly different among the different periods. We cloned and characterized the DGAT2 gene from fruits of I. polycarpa. A partial fragment of 239 bp of IpDGAT2 was amplified by PCR. We cloned the open-reading frame (ORF) of IpDGAT2 by RACE technique. The ORF of IpDGAT2 contains 984 bp and encodes 327 amino acids. The qPCR analysis manifested that IpDGAT2 was expressed in all oil grape growing periods and expression was highest on September 20 (seed maturation). In I. polycarpa fruits the expression of IpDGAT2 was positively correlated with the lipid accumulation rates. Rhodotorula glutinis expression analysis showed that IpDGAT2 have a diacylglycerol acyltransferase bio-functional. Heterologous expression of the 35S::IpDGAT2 in Arabidopsis thaliana confirmed that the isolated IpDGAT2 could catalyze lipid synthesis. The lipid content increased by 40 % in transgenic plants relative to the control. which suggests that high lipid content fruits can be created by the overexpression of IpDGAT2 in I. polycarpa.

High-yield phosphatidylserine production via yeast surface display of phospholipase D from Streptomyces chromofuscus on Pichia pastoris.

The gene encoding phospholipase D (PLD) from Streptomyces chromofuscus was displayed on the cell surface of Pichia pastoris GS115/pKFS-pldh using a Flo1p anchor attachment signal sequence (FS anchor). The displayed PLD (dPLD) showed maximum enzymatic activity at pH 6.0 and 55 °C and was stable within a broad range of temperatures (20-65 °C) and pHs (pH 4.0-11.0). In addition, the thermostability, acid stability and organic solvent tolerance of the dPLD were significantly enhanced compared with the secreted PLD (sPLD) from S. chromofuscus. Use of dPLD for conversion of phosphatidylcholine (PC) and l-serine to phosphatidylserine (PS) showed that 67.5% of PC was converted into PS at the optimum conditions. Moreover, the conversion rate of PS remained above 50% after 7 repeated batch cycles. Thus, P. pastoris GS115/pKFS-pldh shows the potential for viable industrial production of PS.