China National Chemical agreed to buy Swiss pesticide and seeds maker Syngenta for more than $43 billion in cash as the state-backed company extends its shopping spree with what would be the biggest acquisition by a Chinese firm.

ChemChina, as the closely held company is known, offered $465 a share in cash, according to a statement on Wednesday. The offer, endorsed by Syngenta’s board, is about 20 percent higher than the stock’s last close.

Syngenta shares rose 3.8 percent to 407 Swiss francs ($402) in Zurich, remaining below the offer price amid concern the takeover could be delayed by U.S. regulators.

“Political headwinds, in particular from the U.S., could make the takeover process more lengthily than initially expected,” Ute Haibach, an analyst at J. Safra Sarasin, wrote. “The Committee for Foreign Investment in the U.S. will likely watch the transaction closely as China’s domestic seed market is broadly closed to U.S. companies.”

If completed, the deal would help Chairman Ren Jianxin transform ChemChina into the world’s biggest supplier of pesticides and agrochemicals, while snatching an asset coveted by St. Louis-based Monsanto Co. It also underscored the importance China attaches to owning seed and crop-care technology.

The deal is expected to close by year’s end, with a special dividend of 5 Swiss francs a share to be paid if the deal closes. ChemChina plans to keep Syngenta’s management, with Ren chairing a 10-person board that will include four of the existing Syngenta board members.