Most of the time when we go down the path of an agile implementation Gantt charts do not help much. I've seen them used to describe high level plan, almost like a roadmap more as a result of a need to meet a governance standard but not really useful as a tool for managing a project (or dependencies).

This can be an issue for people who have found the use of a gantt chart a useful tool, one that they have used successfully in the past. In other words, this is often a problem for traditional project managers, and for traditional project management governance processes.

The reason gantt charts (or other project management artifacts) are not need is that with agile we set things up so we are producing iterative and incremental “complete” solutions (MVP), building on what we have as we go. Our plan is based on producing value.

In particular, tasks are managed by the team. Dependencies therefore become a lot more localized and dealt with through discussion with the team - we get the next piece of value as a result of having teams task the work required that deliver that value. If they need some task completed first that becomes part of the discussion. Sometimes that discussion will bleed into a prioritization discussion (eg team says “if you want this higher priority value item first, we might be better off doing this lower value item first” or one team talks to another about the relative prioritization's of two team's work) but those conversations should be relatively straight forward and the result is that an item moves up or down in the prioritized backlog.

For additional discussion on Gantt charts at The Demise of the Gantt Chart in Agile Software Projects

Also see Why Doesn't Traditional Project Management Work For Software Projects?