Google is trying to make their Social Media Platform more and more useful for all users. Google added a new recommended Topics section in the home stream which will help you to discover more content on Google+.
The Topics section will show you the content from peoples you added, communities and from collections.
Topics section will show you the things related to your interest. My Google+ profile showing me Topics for Android and Technology.
Google officially announced Topics for Google+ today.
Download Latest Google+ Version to Get this Feature in Mobile