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Improved folate accumulation in genetically modified maize and wheat.

ABSTRACT: Folates are indispensable co-factors for one-carbon metabolism in all organisms. In humans, suboptimal folate intake results in serious disorders. One promising strategy for improving human folate status is to enhance folate levels in food crops by metabolic engineering. In this study, we cloned two GmGCHI (GTP cyclohydrolase I) genes (Gm8gGCHI and Gm3gGCHI) and one GmADCS (aminodeoxychorismate synthase) gene from soybean, which are responsible for synthesizing the folate precursors pterin and p-aminobenzoate, respectively. We initially confirmed their functions in transgenic Arabidopsis plants and found that Gm8gGCHI increased pterin and folate production more than Gm3gGCHI did. We then co-expressed Gm8gGCHI and GmADCS driven by endosperm-specific promoters in maize and wheat, two major staple crops, to boost their folate metabolic flux. A 4.2-fold and 2.3-fold increase in folate levels were observed in transgenic maize and wheat grains, respectively. To optimize wheat folate enhancement, codon-optimized Gm8gGCHI and tomato LeADCS genes under the control of a wheat endosperm-specific glutenin promoter (1Dx5) were co-transformed. This yielded a 5.6-fold increase in folate in transgenic wheat grains (Gm8gGCHI+/LeADCS+). This two-gene co-expression strategy therefore has the potential to greatly enhance folate levels in maize and wheat, thus improving their nutritional value.

SUBMITTER: Liang Q

PROVIDER: S-EPMC6411382 | biostudies-literature | 2019 Mar

REPOSITORIES: biostudies-literature

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Project description:Understanding gene flow in genetically modified (GM) crops is critical to answering questions regarding risk-assessment and the coexistence of GM and non-GM crops. In two field experiments, we tested whether rates of cross-pollination differed between GM and non-GM lines of the predominantly self-pollinating wheat Triticum aestivum. In the first experiment, outcrossing was studied within the field by planting "phytometers" of one line into stands of another line. In the second experiment, outcrossing was studied over distances of 0.5-2.5 m from a central patch of pollen donors to adjacent patches of pollen recipients. Cross-pollination and outcrossing was detected when offspring of a pollen recipient without a particular transgene contained this transgene in heterozygous condition. The GM lines had been produced from the varieties Bobwhite or Frisal and contained Pm3b or chitinase/glucanase transgenes, respectively, in homozygous condition. These transgenes increase plant resistance against pathogenic fungi. Although the overall outcrossing rate in the first experiment was only 3.4%, Bobwhite GM lines containing the Pm3b transgene were six times more likely than non-GM control lines to produce outcrossed offspring. There was additional variation in outcrossing rate among the four GM-lines, presumably due to the different transgene insertion events. Among the pollen donors, the Frisal GM line expressing a chitinase transgene caused more outcrossing than the GM line expressing both a chitinase and a glucanase transgene. In the second experiment, outcrossing after cross-pollination declined from 0.7-0.03% over the test distances of 0.5-2.5 m. Our results suggest that pollen-mediated gene flow between GM and non-GM wheat might only be a concern if it occurs within fields, e.g. due to seed contamination. Methodologically our study demonstrates that outcrossing rates between transgenic and other lines within crops can be assessed using a phytometer approach and that gene-flow distances can be efficiently estimated with population-level PCR analyses.

Project description:This study was conducted to follow up on apparent differences in growth, relative organ sizes, cellular stress and immune function in Atlantic salmon fed genetically modified (GM) Bt-maize compared to the non-modified parental maize line. Gene expression profiling on the distal intestinal segment and liver were performed by the cGRASP 16K salmonid cDNA microarray. Analysis of the intestinal microarray data revealed nearly 500 differentially regulated genes with a false discovery rate of zero, despite modest fold differences (average 2.4 for the down-regulated and 1.7 for the up-regulated genes). However, nine out of ten genes were found not to be significantly different when followed up by quantitative polymerase chain reaction (qPCR), but direction and magnitude of the change was generally confirmed, at least for the up-regulated genes. For the liver microarray data, statistical analyses could not be performed due to constraints in the design. qPCR revealed some differentially regulated genes in the liver, including up-regulation of gelsolin precursor, down-regulation of ferritin heavy subunit and a tendency towards down-regulation of metallothionein B. This, combined with up-regulation of anti-apoptotic protein NR13 and a tendency towards up-regulation of both ferritin heavy chain and metallothionein A and B in the distal intestine, suggests changes in cellular stress/ anti-oxidant status. This corresponds well with, and strengthens previous findings in these fish. To exclude possible confounding factors, the maize ingredients were analyzed for mycotoxins and metabolites, and the GM maize variety contain 90M-NM-<g/kg deoxynivalenol (DON), compared to levels below the detection limit in the non-GM maize. Numerous differences were also seen in the metabolite profiles of the two maize varieties, some of which seem to be connected to the mycotoxin level. The effects on salmon observed in the current and in previous studies correspond relatively well with effects of DON as reported in the literature for other production animals, but knowledge regarding effects and harmful dose levels in fish are practically non-existing, thus it is difficult to conclude whether the observed effects in the fish are caused by the DON level or by some other aspect of the GM maize ingredient.

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Improved folate accumulation in genetically modified maize and wheat.

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