Johnson spent the last two seasons with Detroit, and caught 18 passes for 210 yards in 14 games in 2010. In 123 career games with Arizona, San Francisco and the Lions, he has posted 308 receptions for 3,848 yards and 15 touchdowns.
The Texans also signed tackle Andrew Gardner, and placed four players on the reserve/injured list -- receivers Devard Darling and Lestar Jean, and guards Shelley Smith and Kasey Studdard. Studdard started 14 games for the Texans in 2009.
The team also cut five, including cornerback Antwaun Molden, who appeared in 32 games for the Texans over the past three seasons. Also cut were safety Antonio Baker, rookie punter Brett Hartmann, rookie safety Maurice Rolle and rookie cornerback Jason Teague.