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•E.B. identifies as a novel, edible food source with high nutritional values.•Nutritional profile comparable to quinoa (proteins, reducing sugars, lipids).•Contains higher dietary fibers, ascorbic acid, antioxidant activity and minerals.•Low glycemic index, suitable for diabetic diet.•No significant toxic effect found in safety assessment.

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 ArabidopsisCGS (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.

Cystathionine gamma-synthase (CGS) is a key enzyme of Met biosynthesis in bacteria and plants. Aligning the amino acid sequences revealed that the plant enzyme has an extended N-terminal region that is not found in the bacterial enzyme. However, this region is not essential for the catalytic activity of this enzyme, as deduced from the complementation test of an Escherichia coli CGS mutant. To determine the function of this N-terminal region, we overexpressed full-length Arabidopsis CGS and its truncated version that lacks the N-terminal region in transgenic tobacco (Nicotiana tabacum) plants. Transgenic plants expressing both types of CGS had a significant higher level of Met, S-methyl-Met, and Met content in their proteins. However, although plants expressing full-length CGS showed the same phenotype and developmental pattern as wild-type plants, those expressing the truncated CGS showed a severely abnormal phenotype. These abnormal plants also emitted high levels of Met catabolic products, dimethyl sulfide and carbon disulfide. The level of ethylene, the Met-derived hormone, was 40 times higher than in wild-type plants. Since the alien CGS was expressed at comparable levels in both types of transgenic plants, we further suggest that post-translational modification(s) occurs in this N-terminal region, which regulate CGS and/or Met metabolism. More specifically, since the absence of the N-terminal region leads to an impaired Met metabolism, the results further suggest that this region plays a role in protecting plants from a high level of Met catabolic products such as ethylene.

Spatiotemporal coordination between multiple hormonal pathways is a key determinant of plant growth. This coordination can be mediated by distribution of the auxin network via the action of PIN auxin efflux carriers. We showed that brassinosteroids (BRs) promote cell proliferation and cell expansion of meristematic cells. Hence, roots with high epidermal expression of the BR receptor BRI1 have enlarged meristem whereas bri1mutant has a reduced meristem size. Because the extent of mitotic activity and differentiation is tightly linked to auxin gradient we further asked how the BR pathway integrates with current proposed models for PIN regulation. We showed that the small meristem of BR deficient plants does not involve transcriptional modulation of PIN 1, 3 and 7 genes. Here, we found that PIN2 and PIN4 are under transcriptional regulation. However, their accumulation in the epidermis/cortex and columella respectively was also determined by BRs in a post-transcriptional manner. Thus, BRs impinge on auxin distribution through distinct regulatory modes and the self-organizing auxin system represents at least one mechanism that contributes to BR-mediated growth.