Vitamin E biofortification: enhancement of seed tocopherol concentrations by altered chlorophyll metabolism

Ping Qin; Peng Chen; Yuanwei Zhou; Wei Zhang; Yunyun Zhang; Jingjing Xu; Lu Gan; Yingnan Liu; Jill Romer; Peter Dörmann; Edgar B Cahoon; Chunyu Zhang

doi:10.3389/fpls.2024.1344095

Vitamin E biofortification: enhancement of seed tocopherol concentrations by altered chlorophyll metabolism

Front Plant Sci. 2024 Feb 26:15:1344095. doi: 10.3389/fpls.2024.1344095. eCollection 2024.

Authors

Ping Qin¹, Peng Chen¹, Yuanwei Zhou², Wei Zhang¹, Yunyun Zhang³, Jingjing Xu¹, Lu Gan⁴, Yingnan Liu⁵, Jill Romer⁶, Peter Dörmann⁶, Edgar B Cahoon⁴, Chunyu Zhang¹

Affiliations

¹ National Key Laboratory of Crop Genetic Improvement and College of Plant Science and Technology, Huazhong Agricultural University, Wuhan, China.
² Yichang Academy of Agricultural Science, Ministry of Agriculture and rural areas, Yichang, Hubei, China.
³ Industrial Crops Institute of Yunnan Academy of Agricultural Sciences, Ministry of Agriculture and rural areas, Kunming, China.
⁴ Department of Biochemistry and Center for Plant Science Innovation, University of Nebraska-Lincoln, Lincoln, NE, United States.
⁵ Lincang Agricultural Technology Extension Center, Lincang, Yunnan, China.
⁶ Institute of Molecular Physiology and Biotechnology of Plants (IMBIO), University of Bonn, Bonn, Germany.

Abstract

Homogentisate Phytyltransferase (HPT) catalyzes condensation of homogentisate (HGA) and phytyl diphosphate (PDP) to produce tocopherols, but can also synthesize tocotrienols using geranylgeranyl diphosphate (GGDP) in plants engineered for deregulated HGA synthesis. In contrast to prior tocotrienol biofortification efforts, engineering enhanced tocopherol concentrations in green oilseeds has proven more challenging due to the integral role of chlorophyll metabolism in supplying the PDP substrate. This study show that RNAi suppression of CHLSYN coupled with HPT overexpression increases tocopherol concentrations by >two-fold in Arabidopsis seeds. We obtained additional increases in seed tocopherol concentrations by engineering increased HGA production via overexpression of bacterial TyrA that encodes chorismate mutase/prephenate dehydrogenase activities. In overexpression lines, seed tocopherol concentrations increased nearly three-fold, and resulted in modest tocotrienol accumulation. We further increased total tocochromanol concentrations by enhancing production of HGA and GGDP by overexpression of the gene for hydroxyphenylpyruvate dioxygenase (HPPD). This shifted metabolism towards increased amounts of tocotrienols relative to tocopherols, which was reflected in corresponding increases in ratios of GGDP/PDP in these seeds. Overall, our results provide a theoretical basis for genetic improvement of total tocopherol concentrations in green oilseeds (e.g., rapeseed, soybean) through strategies that include seed-suppression of CHLSYN coupled with increased HGA production.

Keywords: chlorophyll synthase; geranylgeranyl diphosphate; homogentisate; homogentisate phytyltransferase; phytyl diphosphate; tocopherol.

Grants and funding

The author(s) declare financial support was received for the research, authorship, and/or publication of this article. This study is supported by the National Key R&D plan (2022YFD1200400). This research was financially supported by the National Natural Science Foundation of China (Grant No: 31671723 to CZ and Grant No: 31801392 to LG). EC was funded by the United States Department of Agriculture-National Institute of Food and Agriculture, Grant number 2015-67013-22839.