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Arcadia Biosciences has developed rice that uses nitrogen more efficiently, so the plants need less fertilizer. As described in the Guardian yesterday, Arcadia “is working with the Chinese government to reward farmers in China that grow the firm’s genetically modified (GM) rice, with carbon credits that they can sell for cash.”

The rice will reduce fertilizer run off (responsible for oceanic dead zones) and decrease emissions of nitrogen oxide. How does it work? Arcadia’s website isn’t telling all, but I was able to find a paper in the Canadian Journal of Botany: Engineering nitrogen use efficiency with alanine aminotransferase. See the abstract below:

Nitrogen (N) is the most important factor limiting crop productivity worldwide. The ability of plants to acquire N from applied fertilizers is one of the critical steps limiting the efficient use of nitrogen. To improve N use efficiency, genetically modified plants that overexpress alanine aminotransferase (AlaAT) were engineered by introducing a barley AlaAT cDNA driven by a canola root specific promoter (btg26). Compared with wild-type canola, transgenic plants had increased biomass and seed yield both in the laboratory and field under low N conditions, whereas no differences were observed under high N.The transgenics also had increased nitrate influx. These changes resulted in a 40% decrease in the amount of applied nitrogen fertilizer required under field conditions to achieve yields equivalent to wild-type plants.

The first thing I like about their strategy is that they are using a root specific promoter. Plants only absorb nitrogen (N) from their roots, so don’t need N uptake enzymes in other tissues. Even better, the promoter is from the species being transformed so it will presumably work more effectively than a foreign promoter. The researchers chose a barley gene instead of simply using the corresponding rice gene, but there may be a reason that I don’t know about. The protein produced by the gene is one that is native to rice, however, so it is a little closer to cisgenic than transgenic (when compared to bacterial genes and such).

“Alanine aminotransferase (AlaAT) catalyses the reversible transfer of an amino group from glutamate to pyruvate to form 2-oxoglutarate and alanine.” The enzyme is present in virtually all organisms. In plants, AlaAT causes the breakdown of alanine during times of hypoxia (oxygen shortage). “Therefore, AlaAT appears to be crucial for the rapid conversion of alanine to pyruvate during recovery from low-oxygen stress.” [Miyashita et. al.]

So, it sounds like the engineered plants are able to absorb N at a higher rate, and that N goes on along normal pathways to create proteins – resulting in increased yield despite low N concentrations in the soil.

I won’t go into all of the benefits of using less fertilizer here – but there are many. In short, it will save farmers money while being a huge boon for the environment, and producing more food for growing human populations.

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