The Titans signed sixth-round pick Zach Mettenberger on Tuesday and the quarterback’s arrival on the roster serves as a reminder that this is a very big year for incumbent starter Jake Locker. Locker’s contract is up after the season and the Titans didn’t exercise his option for 2015, which means it will be a year-long audition for either continued employment with the Titans or a job with another team. A big part of what he’ll be trying to show is that he can stay healthy for an entire season as a starter, something that’s in doubt after injuries have marred his career thus far. The most recent of those injuries was the foot problem that ended his 2013 season early and forced him to have surgery. He was limited as a result of that operation at coach Ken Whisenhunt’s first minicamp this offseason, but the Titans coach believes Locker will be able to do much more at next week’s OTAs. “He’ll do most everything,” Whisenhunt said, via the Tennessean. “I think he’ll be cleared to participate. But we also have to keep an eye towards not doing too much. … Jake is going to want to throw himself in there, and at this point it is more prudent for us to be reserved in what we do, knowing we’ll have a lot of practices in camp ahead of us and he’ll get opportunities.” Whatever pace they wind up coming, Locker needs to make the most of those opportunities if he wants to have more of them in Nashville.