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New Data Shows Compositional Equivalency between RNAi, Unmodified Soybeans

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NEW YORK (GenomeWeb) – Researchers from China's Ministry of Agriculture last week published new data showing comparable nutrient and anti-nutrient content in short hairpin-expressing and non-transgenic lines of soybeans, adding to the body of evidence showing that RNAi modification does not negatively affect crop plants.

Interest in agricultural applications of RNAi has been steadily growing as firms in the space look to develop new varieties of plants with improved characteristics using the gene-silencing technology.

Already there is at least one RNAi-modified soybean product on the market, Monsanto's Vistive Gold, which uses dsRNA to alter the plant's oil content. Monsanto is also just a few years away from introducing a strain of corn that expresses dsRNA, along with widely used proteins, to combat corn rootworms.

There is also work underway by a number of groups to develop plants that express RNAi constructs to fend of viruses. Yet there are no published data available on the potential nutritional and safety problems associated with plants that use RNAi for viral resistance, the Ministry of Agriculture team wrote in the Journal of Agriculture and Food Chemistry.

As such, the scientists ran a series of chemical analyses on both shRNA-expressing and non-transgenic soybeans to determine whether significant undesirable biological changes occur with the introduction of the RNAi molecules.

The results were then interpreted using the concept of substantial equivalence, which was developed by the United Nations and World Heath Organization and suggests that a transgenic crop is as safe and nutritious as its natural counterpart if no meaningful differences can be found between the two.

Three strains of transgenic soybean plants were created using constructs containing shRNAs against conserved regions of replicase genes of alfalfa mosaic virus (AMV), bean pod mottle virus (BPMV), and soybean mosaic virus (SMV), respectively. All three also included a hairpin targeting the bar gene isolated from Streptomyces hygroscopicus as a selectable marker.

Previously, the lead author of the study published a report showing that shRNAs against AMV, SPMV, and SMV could confer "robust" resistance to these viruses to soybean plants.

A proximate analysis, which provides an overview of food components — in this case, moisture, ash content, crude protein, crude fat, and carbohydrates — showed no statistically significant differences between soybean seeds from the three transgenic plants, or between any of the transgenic plants and unmodified plants.

"Individual values were within the tolerance interval determined for commercial varieties and within published literature ranges," the investigators noted in their paper.

Also evaluated were the plants' amino acid contents, which were expressed on the basis of percentage with respect to total protein levels. The majority of measured amino acids fell within the normal range except for two, which were higher than the maximum listed in the International Life Sciences Institute crop composition database. However, there were no significant differences in the levels of amino acids between the transgenic and non-transgenic soybean seeds.

A similar outcome was observed with fatty acid levels, which were all within normal range except for two that were lower than those listed in the ILSI database. But again, there was no statistical difference between the fatty acid levels of the RNAi and non-RNAi soybean seeds.

The Ministry of Agriculture researchers also looked at the anti-nutrient levels of the soybeans, focusing on lectin and trypsin inhibitors. Both of these were found to be generally low and did not exceed the previously reported range for soybeans. Additionally, the levels of these compounds were similar between the transgenic and traditional soybeans.

Lastly, the isoflavone profiles of the seeds from the different soybean plants were compared. For both they were found to be in the ranges of other commercially available soybeans, with no differences observed between transgenic and non-transgenic strains.

In all cases, the compositional analyses had a confidence level of 95 percent, the investigators wrote in their study. When taken together, the findings indicate that "no significant undesirable biological changes occurred by the insertion of [hairpin RNA]" into the plants. Therefore, these soybeans are as safe and nutritious as their traditional counterparts.

Further, the findings published in the Journal of Agriculture and Food Chemistry may serve as a baseline in the development of RNAi-mediated transgenic soybeans and other crops with broad-spectrum virus resistance, they concluded.

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