By using Add Task from another board option you can quickly search items from other boards and add them to Roadmap and by that create a dependency between these tasks.

You can also include tasks from other boards into your Roadmap by copying their link and inserting it into the Add Task or Add Task from another board fields, and the task will appear on the Roadmap as a linked task and you can track its development stage.

Once a task is updated on one board it will be changed automatically on Roadmap board and vice versa.