A Heteromeric Plastidic Pyruvate Kinase Complex Involved in Seed Oil Biosynthesis inArabidopsis

Abstract

Glycolysis is a ubiquitous pathway thought to be essential for the production of oil in developing seeds of Arabidopsis thaliana and oil crops. Compartmentation of primary metabolism in developing embryos poses a significant challenge for testing this hypothesis and for the engineering of seed biomass production. It also raises the question whether there is a preferred route of carbon from imported photosynthate to seed oil in the embryo. Plastidic pyruvate kinase catalyzes a highly regulated, ATP-producing reaction of glycolysis. The Arabidopsis genome encodes 14 putative isoforms of pyruvate kinases. Three genes encode subunits α, β1, and β2 of plastidic pyruvate kinase. The plastid enzyme prevalent in developing seeds likely has a subunit composition of 4α4β1, is most active at pH 8.0, and is inhibited by Glu. Disruption of the gene encoding the β1 subunit causes a reduction in plastidic pyruvate kinase activity and 60% reduction in seed oil content. The seed oil phenotype is fully restored by expression of the β1 subunit–encoding cDNA and partially by the β2 subunit–encoding cDNA. Therefore, the identified pyruvate kinase catalyzes a crucial step in the conversion of photosynthate into oil, suggesting a preferred plastid route from its substrate phosphoenolpyruvate to fatty acids.

A comparative transcriptomic approach to understanding the formation of cork

“…Some genes related to these categories, such as the putative orthologs of Arabidopsis sucrose synthase SUS4 and the plastidial pyruvate kinase PKp1, are clearly upregulated in the cork oak outer bark (Table S6B). In fact the plastidial pyruvate kinase has been involved in fatty acid synthesis in Arabidopsis seeds (Andre et al 2007;Baud et al 2007) and sucrose synthase is involved in oil accumulation, suggesting a coordination between glycolytic and fatty acid biosynthetic pathways (Troncoso-Ponce et al 2011). However, the upregulation of sucrose synthases in cork could also be a consequence of a higher demand of cell wall synthesis (Andersson-Gunnerås et al 2006;Wei et al 2015).…”

AtABCA9 transporter supplies fatty acids for lipid synthesis to the endoplasmic reticulum

“…To identify the ABC transporters involved in fatty acid transport to the ER, we grew seeds of KO mutants of eight ABCA family members on half-strength Murashige and Skoog (1/2 MS) medium with or without sucrose, and compared early seedling growth with WT. The rationale behind this test is that early seedling growth of oilseed plants depends on storage lipids in the absence of sucrose, but not in its presence (11,12). Thus, plants defective in expression of fatty acid-transporting ABC transporter would be expected to exhibit reduced growth in the absence of sucrose, but normal growth in its presence.…”

“…Together with the defective seed morphology, this expression pattern suggests that ABCA9 functions during seed development. To test this, we evaluated developing seeds at 4,8,12,16, and 20 d after flowering (DAF) (Fig. 1D).…”

Microalgal triacylglycerols as feedstocks for biofuel production: perspectives and advances

“…In oil seed plants, a major route of carbon flux to fatty acid synthesis may involve cytosolic glycolysis to phosphoenolpyruvate (PEP), which is then preferentially transported from the cytosol to the plastid, where it is converted to pyruvate and consequently to acetyl CoA (Baud et al, 2007;Ruuska et al, 2002;Schwender and Ohlrogge, 2002). In green algae, as glycolysis and pyruvate kinase (PK), which catalyzes the irreversible synthesis of pyruvate from PEP, occur in the chloroplast in addition to the cytosol (Andre et al, 2007), it is possible that glycolysis-derived pyruvate is the major photosynthate to be converted to acetyl CoA for de novo fatty acid synthesis. An ACCase is generally considered to catalyze the first reaction of the fatty acid biosynthetic pathway -the formation of malonyl CoA from acetyl CoA and CO 2 .…”