A Pair of Arabidopsis Diacylglycerol Kinases Essential for Gametogenesis and Endoplasmic Reticulum Phospholipid Metabolism in Leaves and Flowers.

Phosphatidic acid (PA) is a key phospholipid in glycerolipid metabolism and signaling. Diacylglycerol kinase (DGK) produces PA by phosphorylating diacylglycerol, a crucial step in PA metabolism. Although DGK activity is known to be involved in plant development and stress response, how specific DGK isoforms function in development and phospholipid metabolism remains elusive. Here, we showed that Arabidopsis (Arabidopsis thaliana) DGK2 and DGK4 are crucial for gametogenesis and biosynthesis of phosphatidylglycerol and phosphatidylinositol in the endoplasmic reticulum (ER). With comprehensive transcriptomic data of seven DGKs and genetic crossing, we found that dgk2-1/- dgk4-1/- plants were gametophyte lethal, although parental single homozygous plants were viable. The dgk2-1/+ dgk4-1/+ double heterozygote showed defective pollen tube growth and seed development because of nonviable mutant gametes. DGK2 and DGK4 were localized to the ER and were involved in PA production for pollen tube growth. Transgenic knockdown lines of DGK2 and DGK4 confirmed the gametophyte defect and also revealed defective leaf and root growth. Glycerolipid analysis in the knockdown lines showed that phosphatidylglycerol and phosphatidylinositol metabolism was affected differently in floral buds and leaves. These results suggest that DGK2 and DGK4 are essential during gametogenesis and are required for ER-localized phospholipid metabolism in vegetative and reproductive growth.

Expression Profiles of 2 Phosphate Starvation-Inducible Phosphocholine/Phosphoethanolamine Phosphatases, PECP1 and PS2, in Arabidopsis.

Phosphorus is essential for plant viability. Phosphate-starved plants trigger membrane lipid remodeling to replace membrane phospholipids by non-phosphorus galactolipids presumably to acquire scarce phosphate source. Phosphoethanolamine/phosphocholine phosphatase 1 (PECP1) and phosphate starvation-induced gene 2 (PS2) belong to an emerging class of phosphatase induced by phosphate starvation and dephosphorylates phosphocholine and phosphoethanolamine (PEtn) in vivo. However, detailed spatiotemporal expression pattern as well as subcellular localization has not been investigated yet. Here, by constructing transgenic plants harboring functional translational promoter-reporter fusion system, we showed the expression pattern of PECP1 and PS2 in different tissues and in response to phosphate starvation. Besides, the Venus fluorescent reporter revealed that both are localized at the ER. Characterization of transgenic plants that overexpress PECP1 or PS2 showed that their activity toward PEtn may be different in vivo. We suggest that PECP1 and PS2 are ER-localized phosphatases that show similar expression pattern yet have a distinct substrate specificity in vivo.

Arabidopsis Serine Decarboxylase 1 (SDC1) in Phospholipid and Amino Acid Metabolism.

Arabidopsis thaliana serine decarboxylase 1 (SDC1) catalyzes conversion of serine to ethanolamine, the first reaction step of phosphatidylcholine and phosphatidylethanolamine biosynthesis. However, an involvement of SDC1 in amino acid metabolism remains elusive despite that serine is the substrate of SDC1. Here, we showed that SDC1 localizes in mitochondria although phosphatidylcholine and phosphatidylethanolamine are known to be produced in the endoplasmic reticulum (ER). Moreover, we found that overexpression of SDC1 decreased levels of amino acid compounds derived from mitochondrial tricarboxylic acid cycle. These results suggest that mitochondria-localized SDC1 plays an important role in both phospholipid and amino acid metabolism in A. thaliana.

Biocompatibility and drug release behavior of curcumin conjugated gold nanoparticles from aminosilane-functionalized electrospun poly(N-vinyl-2-pyrrolidone) fibers.

Curcumin (CUR) has a wide spectrum of biological and pharmacological activities, yet problems of its bioavailability remained a major challenge in preclinical studies. Thus, the design of the delivery systems with CUR as a model drug featuring dual release process - an initial burst followed by sustained release - to provide the optimal drug pharmacokinetics in the therapeutic region has been actively pursued. In this study, the 3-aminopropyltriethoxysilane (APTES)-functionalized electrospun poly(N-vinyl-2-pyrrolidone) fibers (NH2-PVP) were utilized as a free-standing substrate for the immobilization of CUR-PVP capped gold nanoparticles (CUR-PGNPs) conjugates. The conjugate was synthesized by sonication and the drug entrapment percentage was determined to be 54.2 ±1.8. CUR-PGNPs immobilized on NH2-PVP fibers showed a moderate burst release during the first few hours, followed by a sustained release lasting for 2days. The drug release was found pH-dependent (pH 5.0>6.0>7.4). The two-stage release profiles of CUR-PGNPs@NH2-PVP fibers were fitted well to Korsmeyer-Peppas model, indicating a non-Fickian diffusion mechanism for initial burst release and Fickian diffusion-controlled mechanism for the sustained release. Initial biocompatibility assessments based on lactate dehydrogenase (LDH) assay and morphological examination by SEM with L-929 mouse fibroblasts revealed that CUR-PGNPs@NH2-PVP nanofibrous scaffold was capable of supporting cell growth over a culture period of 3days.