Improved fruit α-tocopherol, carotenoid, squalene and phytosterol contents through manipulation of Brassica juncea 3-HYDROXY-3-METHYLGLUTARYL-COA SYNTHASE1 in transgenic tomato.

Pan Liao,Xinjian Chen,Mingfu Wang,Thomas J Bach,Mee-Len Chye

doi:10.1111/pbi.12828

Abstract

Summary3‐Hydroxy‐3‐methylglutaryl‐coenzyme A synthase (HMGS) in the mevalonate (MVA) pathway generates isoprenoids including phytosterols. Dietary phytosterols are important because they can lower blood cholesterol levels. Previously, the overexpression of Brassica juncea wild‐type (wt) and mutant (S359A) BjHMGS1 in Arabidopsis up‐regulated several genes in sterol biosynthesis and increased sterol content. Recombinant S359A had earlier displayed a 10‐fold higher in vitro enzyme activity. Furthermore, tobacco HMGS overexpressors (OEs) exhibited improved sterol content, plant growth and seed yield. Increased growth and seed yield in tobacco OE‐S359A over OE‐wtBjHMGS1 coincided with elevations in NtSQS expression and sterol content. Herein, the overexpression of wt and mutant (S359A) BjHMGS1 in a crop plant, tomato (Solanum lycopersicum), caused an accumulation of MVA‐derived squalene and phytosterols, as well as methylerythritol phosphate (MEP)‐derived α‐tocopherol (vitamin E) and carotenoids, which are important to human health as antioxidants. In tomato HMGS‐OE seedlings, genes associated with the biosyntheses of C10, C15 and C20 universal precursors of isoprenoids, phytosterols, brassinosteroids, dolichols, methylerythritol phosphate, carotenoid and vitamin E were up‐regulated. In OE‐S359A tomato fruits, increased squalene and phytosterol contents over OE‐wtBjHMGS1 were attributed to heightened SlHMGR2, SlFPS1, SlSQS and SlCYP710A11 expression. In both tomato OE‐wtBjHMGS1 and OE‐S359A fruits, the up‐regulation of SlGPS and SlGGPPS1 in the MEP pathway that led to α‐tocopherol and carotenoid accumulation indicated cross‐talk between the MVA and MEP pathways. Taken together, the manipulation of BjHMGS1 represents a promising strategy to simultaneously elevate health‐promoting squalene, phytosterols, α‐tocopherol and carotenoids in tomato, an edible fruit.

Highlights

In plant cells, isoprenoids including phytosterols, sesquiterpenes, monoterpenes, cytokinins (CKs), carotenoids, vitamin E, dolichol and brassinosteroids (BRs) are generated via the mevalonate (MVA) pathway and/or the methylerythritol phosphate (MEP) pathway (Akhtar et al, 2013; Besser et al, 2009; Enfissi et al, 2010; Rodrıguez-Concepcion and Gruissem, 1999; Sallaud et al, 2009)
Resembling tobacco Hydroxy-3-methylglutaryl-coenzyme A synthase (HMGS)-OEs, tomato HMGS-OEs showed an enhanced expression of SlHMGR1, SlSQS, SlGGPPS1 and SlCYP85A1 and an increase in growth accompanied by a decline in SlHMGS2 and SlIPI expression
Sterol content was elevated in HMGS-OE tomato fruits, confirming that elevation of health-promoting components was achieved via metabolic engineering of BjHMGS1 in tomato fruit and that extended phytosterol enhancement in fruits was attained using mutant S359A

Summary

3-Hydroxy-3-methylglutaryl-coenzyme A synthase (HMGS) in the mevalonate (MVA) pathway generates isoprenoids including phytosterols. The overexpression of wt and mutant (S359A) BjHMGS1 in a crop plant, tomato (Solanum lycopersicum), caused an accumulation of MVA-derived squalene and phytosterols, as well as methylerythritol phosphate (MEP)-derived a-tocopherol (vitamin E) and carotenoids, which are important to human health as antioxidants. In tomato HMGS-OE seedlings, genes associated with the biosyntheses of C10, C15 and C20 universal precursors of isoprenoids, phytosterols, brassinosteroids, dolichols, methylerythritol phosphate, carotenoid and vitamin E were up-regulated. In OE-S359A tomato fruits, increased squalene and phytosterol contents over OE-wtBjHMGS1 were attributed to heightened SlHMGR2, SlFPS1, SlSQS and SlCYP710A11 expression. In both tomato OE-wtBjHMGS1 and OE-S359A fruits, the up-regulation of SlGPS and SlGGPPS1 in the MEP pathway that led to a-tocopherol and carotenoid accumulation indicated cross-talk between the MVA and MEP pathways. The manipulation of BjHMGS1 represents a promising strategy to simultaneously elevate health-promoting squalene, phytosterols, a-tocopherol and carotenoids in tomato, an edible fruit

Introduction

Results

Discussion

Experimental procedures