Gbenameto said they were charged late Monday following their arrests on Sunday.
On Monday, Gbenameto had announced their arrests and described the alleged plot to kill Yayi, also the current chairman of the African Union.
Those arrested were Moudjaidou Soumanou, former minister of commerce; Yayi's personal doctor Ibrahim Mama Cisse; and Zouberath Kora-Seke, one of Yayi's nieces who worked at the presidency.
It was alleged that the president's niece and his doctor were promised one billion CFA francs (1.5 million euros, $2 million) to replace Yayi's anti-pain medicine with poison.
An aide to the president, speaking on condition of anonymity, has alleged that the plot may have been linked to a decision to end the monopoly of a company supplying materials for the cotton industry as well as a major port contract.
