Storage oil mobilization starts with the onset of seed germination. Oil bodies packed with triacylglycerol (TAG) exist in close proximity with glyoxysomes, the single membrane-bound organelles that house most of the biochemical machinery required to convert fatty acids derived from TAG to 4-carbon compounds. The 4-carbon compounds in turn are converted to soluble sugars that are used to fuel seedling growth. Biochemical analysis over the last 50 years has identified the main pathways involved in this process, including beta-oxidation, the glyoxylate cycle, and gluconeogenesis. In the last few years molecular genetic dissection of the overall process in the model oilseed species Arabidopsis has provided new insight into its complexity, particularly with respect to the specific role played by individual enzymatic steps and the subcellular compartmentalization of the glyoxylate cycle. Both abscisic acid (ABA) and sugars inhibit storage oil mobilization and a substantial degree of the control appears to operate at the transcriptional level.

Seed Storage Oil Mobilization

INTRODUCTION 159 SOURCES OF MICROBODIES: MICROBODY CONSTITUENTS 162 Glyoxysomes...... ....... ........ ... ...... ... ..... 162 Leaf Peroxisomes 164 Microbodies from Other Tissues ...... 164 DISTRIBUTION OF ENZYMES WITHIN MICROBODIES 165 ISOENZYMES IN GLYOXYSOMES AND LEAF PEROXISOMES 166 Isoenzymes of MDH 166 Isoenzymes of Citrate Synthetase 167 Isoenzymes of Aspartate-a.-Ketoglutarate Transaminase 168 FUNCTIONS OF GLYOXYSOMES AND LEAF PEROXISOMES 168 DEVELOPMENT OF MICROBODIES 170 Glyoxysome Biogenesis ..... ,", . . . . . . . . . . . . . . ,. 170 Biogenesis of Leaf Peroxisomes 176 Microbody Transition in Fatty Cotyledons 177 Hormonal Influences 185 CONCLUSIONS , ...... , 186

Microbodies in Higher Plants

Acetyl-CoA carboxylase (ACCase) catalyzes the first committed step of fatty acid synthesis, the carboxylation of acetyl-CoA to malonyl-CoA. Two physically distinct types of enzymes are found in nature. Heteromeric ACCase composed of four subunits is usually found in prokaryotes, and homomeric ACCase composed of a single large polypeptide is found in eukaryotes. Most plants have both forms, the heteromeric form in plastids, in which de novo fatty acids are synthesized, and the homomeric form in cytosol. This review focuses on the structure and regulation of plant heteromeric ACCase and its manipulation for plant breeding.

https://www.tandfonline.com/doi/pdf/10.1271/bbb.68.1175

Plant acetyl-CoA carboxylase: structure, biosynthesis, regulation, and gene manipulation for plant breeding.

Many plants deposit TAG in seeds and fruits as the major form of storage lipid. TAG production is of tremendous socioeconomic value in food, nutraceutical, and industrial applications, and thus numerous conventional and molecular genetic strategies have been explored in attempts to increase TAG content and modify the FA composition of plant seed oils. Much research has focused on the acyl-CoA-dependent reaction catalyzed by diacylglycerol acyltransferase (DGAT), which is an integral endoplasmic reticulum protein and has also been shown to be present in oil bodies and plastids. DGAT enzymes exhibit diverse biochemical properties among different plant species, many of which are summarized here. In addition to catalyzing a critical step in TAG biosynthesis, there is evidence that DGAT has roles in lipid metabolism associated with germination and leaf senescence. TAG can also be formed in plants via two different acyl-CoA-independent pathways, catalyzed by phospholipid: diacylglycerol acyltransferase and diacylglycerol transacylase. The current understanding of the terminal step in TAG formation in plants and the development of molecular genetic approaches aimed at altering TAG yield and FA composition of TAG are discussed.

Diacylglycerol acyltransferase: a key mediator of plant triacylglycerol synthesis.

Polyketide natural products show great promise as medicinal agents. Typically the products of microbial secondary biosynthesis, polyketides are synthesized by an evolutionarily related but architecturally diverse family of multifunctional enzymes called polyketide synthases. A principal limitation for fundamental biochemical studies of these modular megasynthases, as well as for their applications in biotechnology, is the challenge associated with manipulating the natural microorganism that produces a polyketide of interest. To ameliorate this limitation, over the past decade several genetically amenable microbes have been developed as heterologous hosts for polyketide biosynthesis. Here we review the state of the art as well as the difficulties associated with heterologous polyketide production. In particular, we focus on two model hosts, Streptomyces coelicolor and Escherichia coli. Future directions for this relatively new but growing technological opportunity are also discussed.

https://mmbr.asm.org/content/mmbr/65/1/106.full.pdf

S. Matsumura

Papers

Fat metabolism in higher plants