Mo. Rev. Stat. § 106.010

The governor shall have power and he is hereby authorized to remove from office, without assigning any other reason therefor, any appointive state official required by law to be appointed by the governor, whenever in his opinion such removal is necessary for the betterment of the public service, but the governor may, at his discretion, in any order of removal which he may make under authority of this section, assign additional and more specific reasons for such removal.