Guion left Florida State after his junior season. The 6-foot-4, 303-pound lineman started 14 games for the Seminoles.
Johnson caught 36 passes for 613 yards and seven touchdowns for Jackson State last season. He returned a punt for a touchdown as a senior as well and should get a look on special teams as a return man.
The moves assure that both players will be on time for training camp, which opens Friday.
Johnson signed a four-year contract for the rookie minimum salary, his agent, Angelo Wright, said.