Constitutive expression of feedback-insensitive cystathionine γ-synthase increases methionine levels in soybean leaves and seeds
YU Yang1*, HOU Wen-sheng1*, Yael Hacham2, 3*, SUN Shi1, WU Cun-xiang1, Ifat Matityahu2, SONG Shi-kui1, Rachel Amir2, 3, HAN Tian-fu1
1 Key Laboratory of Soybean Biology (Beijing), Ministry of Agriculture/Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing 100081, P.R.China 2 Laboratory of Plant Science, Migal Galilee Technology Center, Kiryat Shmona 12100, Israel 3 Tel-Hai College, Upper Galilee 11016, Israel
Abstract Soybean (Glycine max (L.) Merr.) is a major crop that provides plant-origin protein and oil for humans and livestock. Although the soybean vegetative tissues and seeds provide a major source of high-quality protein, they suffer from low concentration of an essential sulfur-containing amino acid, methionine, which significantly limits their nutritional quality. The level of methionine is mainly controlled by the first unique enzyme of methionine synthesis, cystathione γ-synthase (CGS). Aiming to elevate methionine level in vegetative tissues and seeds, we constitutively over-expressed a feedback-insensitive
Arabidopsis CGS (AtD-CGS) in soybean cultivars, Zigongdongdou (ZD) and Jilinxiaoli 1 (JX). The levels of soluble methionine increased remarkably in leaves of transgenic soybeans compared to wild-type plants (6.6- and 7.3-fold in two transgenic ZD lines, and 3.7-fold in one transgenic JX line). Furthermore, the total methionine contents were significantly increased in seeds of the transgenic ZD lines (1.5- to 4.8-fold increase) and the transgenic JX lines (1.3- to 2.3-fold increase) than in the wild type. The protein contents of the transgenic soybean seeds were significantly elevated compared to the wild type, suggesting that the scarcity of methionine in soybeans may limit protein accumulation in soybean seeds. The increased protein content did not alter the profile of major storage proteins in the seeds. Generally, this study provides a promising strategy to increase the levels of methionine and protein in soybean through the breeding programs.
This work was supported by the Major Science and Technology Projects of China (2014ZX08004-003, 2014ZX08010-004), the Natural Science Foundation of China (31471571), the earmarked fund for China Agriculture Research System (CARS-04), and the Agricultural Science and Technology Innovation Project of CAAS, as well as by Israel Science Foundation (ISF grant 231-09).
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