Jim Harbaugh (with Alex Smith) looks on Josh Johnson as a ‘beloved son.” (Paul Sakuma / AP)

Josh Johnson, Harbaugh’s quarterback at the University of San Diego, signed a two-year deal with the team, making for a QB quartet of Alex Smith, Colin Kaepernick and Scott Tolzien.

Johnson spent last season with Tampa Bay and, before the Bucs played the 49ers last fall, Harbaugh said Johnson was like a “beloved son.” This son, though, is ready to play some serious football.

“I will compete with anybody, any time, anywhere,” Johnson said in July (via Eric Branch of the San Francisco Chronicle). “Putting a title on anything is just a title. Titles can be changed. So however our situation plays out, I’m fine with competing. I’ve been doing it my whole life. I wouldn’t have it any other way.”

In four seasons in the NFL, Johnson has started five games, throwing five touchdown passes and 10 interceptions for a 57.7 passer rating. Maybe Harbaugh can change that.

“He makes your strengths become your greatness,” Johnson said, “and makes your weaknesses become your strengths.”