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

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

JOURNAL=Frontiers in Plant Science

VOLUME=15

YEAR=2024

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2024.1344095

DOI=10.3389/fpls.2024.1344095

ISSN=1664-462X

ABSTRACT=<p>Homogentisate Phytyltransferase (<italic>HPT</italic>) 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 <italic>CHLSYN</italic> coupled with <italic>HPT</italic> overexpression increases tocopherol concentrations by &gt;two-fold in Arabidopsis seeds. We obtained additional increases in seed tocopherol concentrations by engineering increased HGA production via overexpression of bacterial <italic>TyrA</italic> 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 <italic>CHLSYN</italic> coupled with increased HGA production.</p>