Expression of malic enzyme reveals subcellular carbon partitioning for storage reserve production in soybeans

Abstract

Summary Central metabolism produces amino and fatty acids for protein and lipids that establish seed value. Biosynthesis of storage reserves occurs in multiple organelles that exchange central intermediates including two essential metabolites, malate, and pyruvate that are linked by malic enzyme. Malic enzyme can be active in multiple subcellular compartments, partitioning carbon and reducing equivalents for anabolic and catabolic requirements. Prior studies based on isotopic labeling and steady‐state metabolic flux analyses indicated malic enzyme provides carbon for fatty acid biosynthesis in plants, though genetic evidence confirming this role is lacking. We hypothesized that increasing malic enzyme flux would alter carbon partitioning and result in increased lipid levels in soybeans. Homozygous transgenic soybean plants expressing Arabidopsis malic enzyme alleles, targeting the translational products to plastid or outside the plastid during seed development, were verified by transcript and enzyme activity analyses, organelle proteomics, and transient expression assays. Protein, oil, central metabolites, cofactors, and acyl‐acyl carrier protein (ACPs) levels were quantified overdevelopment. Amino and fatty acid levels were altered resulting in an increase in lipids by 0.5–2% of seed biomass (i.e. 2–9% change in oil). Subcellular targeting of a single gene product in central metabolism impacts carbon and reducing equivalent partitioning for seed storage reserves in soybeans.

Differential gene expression provides leads to environmentally regulated soybean seed protein content

“…This mechanism serves are an optimal target for genetic engineering/control of the decision between lipid and protein biosynthesis. Increasing expression of malic enzyme would make a molecular conduit to directing nitrogen and carbon toward lipid biosynthesis and away from protein biosynthesis, serving as a molecular switch for the accumulation of major seed storage biomolecules ( Morley et al., 2023 ).…”

Physcomitrium patens response to elevated CO2 is flexible and determined by an interaction between sugar and nitrogen availability

“…7; Scenario 3), yet the nitrogen assimilation and amino acid levels are similar for BCLD‐ and BCD‐grown plants. This suggests that under replete carbon scenario, nitrogen is not the limiting factor, but perhaps the amount of reduced cofactors are insufficient to support biosynthetic processes in metabolism (Allen, 2016a,b; Morley et al ., 2023) and more specifically, the reduction in nitrate to ammonia that requires multiple reducing equivalents. In BCDAT plants, ammonium ions lead to production of higher levels of amino acids, fewer carbohydrates, and lower T6P (Fig.…”

Walking the ‘design–build–test–learn’ cycle: flux analysis and genetic engineering reveal the pliability of plant central metabolism

“…In an article published in this issue of New Phytologist , Morley et al . (2023; 1834–1851) put the insights they have gained into the delivery of metabolic precursors and energy cofactors to oil synthesis to the test and arrive at a successful metabolic engineering design. They show that an increase in seed oil content in soybeans can be achieved by overexpression of malic enzyme (ME) during seed development.…”

“…Previous metabolic studies on soybeans using isotopic tracers and metabolic flux analysis have provided insight into how lipid and protein biosynthesis occurs simultaneously during seed development (Allen et al, 2009;Allen & Young, 2013;Kambhampati et al, 2021). In an article published in this issue of New Phytologist, Morley et al (2023;1834-1851 put the insights they have gained into the delivery of metabolic precursors and energy cofactors to oil synthesis to the test and arrive at a successful metabolic engineering design. They show that an increase in seed oil content in soybeans can be achieved by overexpression of malic enzyme (ME) during seed development.…”