Since Planar Nexus has the subtypes Urza's, Mine, Power-Plant, and Tower, it will satisfy all of the requirements for the abilities of Urza's Mine, Urza's Power Plant, and Urza's Tower to add additional mana. For example, if you control Planar Nexus and Urza's Tower, the ability of Urza's Tower will add {C}{C}{C}.

The list of nonbasic land types in the reminder text is exhaustive as of the release of Modern Horizons 3. The full list of land types can always be found in the Comprehensive Rules of Magic.