Combined transcript, proteome, and metabolite analysis of transgenic maize seeds engineered for enhanced carotenoid synthesis reveals pleotropic effects in core metabolism.

Mathilde Decourcelle,Gerhard Sandmann,Linhdavanh Couvelard,Changfu Zhu,Paul Fraser,Teresa Capell,Sonia Hem,Sabine Steiger,Paul Christou,Laura Perez-Fons,Sylvain Baulande

doi:10.1093/jxb/erv120

Abstract

The aim of this study was to assess whether endosperm-specific carotenoid biosynthesis influenced core metabolic processes in maize embryo and endosperm and how global seed metabolism adapted to this expanded biosynthetic capacity. Although enhancement of carotenoid biosynthesis was targeted to the endosperm of maize kernels, a concurrent up-regulation of sterol and fatty acid biosynthesis in the embryo was measured. Targeted terpenoid analysis, and non-targeted metabolomic, proteomic, and transcriptomic profiling revealed changes especially in carbohydrate metabolism in the transgenic line. In-depth analysis of the data, including changes of metabolite pools and increased enzyme and transcript concentrations, gave a first insight into the metabolic variation precipitated by the higher up-stream metabolite demand by the extended biosynthesis capacities for terpenoids and fatty acids. An integrative model is put forward to explain the metabolic regulation for the increased provision of terpenoid and fatty acid precursors, particularly glyceraldehyde 3-phosphate and pyruvate or acetyl-CoA from imported fructose and glucose. The model was supported by higher activities of fructokinase, glucose 6-phosphate isomerase, and fructose 1,6-bisphosphate aldolase indicating a higher flux through the glycolytic pathway. Although pyruvate and acetyl-CoA utilization was higher in the engineered line, pyruvate kinase activity was lower. A sufficient provision of both metabolites may be supported by a by-pass in a reaction sequence involving phosphoenolpyruvate carboxylase, malate dehydrogenase, and malic enzyme.

Highlights

Carotenoids are essential nutritional factors of the human derived by cleavage of carotenoids like β-carotene (as prodiet (Rao and Rao, 2007) which are needed for good vision vitamin A) with an unsubstituted β-ionone end group
Our results identified the key adaptations of sugar metabolism which are necessary to fuel the higher through-put via the carotenoid pathway
The crucial step of increasing carotenoid content in Ph3 was the over-production of phytoene synthase (Figs 1; 3A) which has been shown in different plant species to limit carotenoid synthesis (Sandman et al, 2006)

Summary

Introduction

Carotenoids are essential nutritional factors of the human derived by cleavage of carotenoids like β-carotene (as prodiet (Rao and Rao, 2007) which are needed for good vision vitamin A) with an unsubstituted β-ionone end group. Retinal, which is the light sensor in our eye, is addition, the yellow eye spot, the macula, protects the retina. A constant supply of both nutritional carotenoids prevents the degradation of the macula which results in a loss of vision especially in elderly people (SanGiovanni and Neuringer, 2012). Several carotenoids are important as food additives. The highest demands on natural and synthetic carotenoids relates to salmon and poultry farming (Tyczkowski and Hamilton, 1986)

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