Dec 14 (Reuters) - Calyxt Inc said on Monday it had agreed to sell all the gene-edited soybean grains it produced in 2020 to agricultural merchant Archer Daniels Midland Co amid a supply shortage in the United States.

Rising demand from domestic grain processors and lower global stockpiles due to a months-long dry spell in Argentina, has led to an expectation that U.S. soybean ending stocks for the 2020/21 marketing year would be at their lowest level in seven years.

The stocks were seen at 175 million bushels, while analysts were expecting the report to show U.S. soybean stocks of 168 million bushels.

The forecast for world soybean stocks was cut to 85.64 million tonnes from 86.52 million tonnes, against expectations for 85.11 million tonnes, based on an average of estimates given in a Reuters poll.

The food and agriculture biotech company said the sales of about four million bushels of soybean grains, which have zero trans fat per serving and lower saturated fats, began in the third quarter and will continue through late 2021.

Calyxt declined to provide an exact deal value, but said it charged a premium to market prices.

Soybean prices were around $11.50 per bushel and the deal would contribute at least $45 million to Calyxt's revenue, excluding the premium it would charge for the grains, the company said.

As part of the deal, Archer Daniels will crush the grain as well as market and sell the resulting oil and meal.

Calyxt launched the soybean in 2019 as the first commercially approved gene-edited food in the United States.

(Reporting by Arathy S Nair in Bengaluru; Editing by Amy Caren Daniel)