Transgenic tomato overexpressing Brassica juncea 3-HYDROXY-3-METHYLGLUTARYL-COA SYNTHASE1 enhances health-promoting vitamin E, carotenoids, squalene and phytosterols

Abstract

Transgenic tomato overexpressing Brassica juncea 3-HYDROXY-3-METHYLGLUTARYL-COA SYNTHASE1 enhances health-promoting vitamin E, carotenoids, squalene and phytosterols Pan Liao1,2, Xinjian Chen1, Mingfu Wang1, Thomas J. Bach3, Mee-Len Chye1,2* 1School of Biological Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong, China. 2Partner State Key Laboratory of Agrobiotechnology (CUHK). 3Centre National de la Recherche Scientifique, UPR 2357, Institut de Biologie Moléculaire des Plantes, 67083 Strasbourg, France. *Corresponding author: mlchye@hku.hk Isoprenoids consist of a large group of functional natural products. For instance, dietary phytosterols are known to lower blood cholesterol levels. 3-Hydroxy-3-methylglutaryl-coenzyme A synthase (HMGS) is the second enzyme in the mevalonate (MVA) pathway which generate isoprenoids including phytosterols [1,2]. Previous studies on the enzyme kinetics of recombinant wild-type (wt) and mutant Brassica juncea HMGS1 had shown that the HMGS mutant enzyme S359A had a 10-fold higher activity [3]. Furthermore, the overexpression of B. juncea wt and mutant (S359A) BjHMGS1 in Arabidopsis upregulated native HMGR, SMT2, DWF1, CYP710A1 and BR60X2, thereby increasing sterol content [4]. Also, tobacco HMGS-overexpressors (OEs) enhanced native NtHMGR1, NtIPI2, NtSQS, NtSMT1-2, NtSMT2-1, NtSMT2-2 and NtCYP85A1 expression in seedlings, improving sterol content, plant growth and seed yield [5]. When wt and mutant (S359A) BjHMGS1 were overexpressed in a crop plant tomato (Solanum lycopersicum), gas chromatography–mass spectrometry (GC-MS) and high-performance liquid chromatography (HPLC) results showed that not only did the MVA-derived squalene and sterols, but also the methylerythritol phosphate (MEP)-derived carotenoids and vitamin E (α-tocopherol), increased, revealing crosstalk between the MVA and MEP pathways. Furthermore, OE-S359A fruits displayed greater squalene and phytosterol content than OE-wtBjHMGS1, as a result of higher expression of SlHMGR2, SlFPS1, SlGPS, SlSQS and SlCYP710A11 [6]. In summary, the manipulation of BjHMGS1 represents a promising strategy to simultaneously enhance health-promoting squalene, phytosterols, carotenoids and vitamin E in an edible fruit. This work was supported by the Wilson and Amelia Wong Endowment Fund, Research Grants Council of Hong Kong (AoE/M-05/12), Innovation Technology Fund of the Innovation Technology Commission (Support to Partner State Key Laboratories in Hong Kong) and HKU CRCG awards (0910159039, 1007160002, 1511159010). PL was supported by a University Postgraduate Fellowship and a Postdoctoral Fellowship. 1. Liao P, Hemmerlin A, Bach TJ, Chye ML. Biotechnol Adv, 2016, 34, 697-713. 2. Liao P, Wang H, Hemmerlin A, Nagegowda DA, Bach TJ, Wang M, Chye ML. Plant Cell Rep, 2014, 33, 1005- 1022. 3. Nagegowda DA, Bach TJ, Chye ML. Biochem J, 2004, 383, 517-527. 4. Wang H, Nagegowda DA, Rawat R, Bouvier-Navé P, Guo D, Bach TJ, Chye ML. Plant Biotechnol J, 2012, 10, 31-42. 5. Liao P, Wang H, Wang M, Hsiao AS, Bach TJ, Chye ML. PLoS One, 2014, 9, e98264. 6. Liao P, Chen X, Wang M, Bach TJ, Chye ML. Plant Biotechnol J, 2017, (DOI: 10.1111/pbi.12828).