There's a relationship between the Planck length and gravity, because the Planck length is the lower bound on distances for which we can make meaningful scientific predictions, and length is a relationship defined between two points in space, the curvature of which, is responsible for gravity. Furthermore, due to Einstein's realization that that the field through which the gravitational force is propagated, is curved spacetime itself, there is an expectation that just as with the other fundamental forces, there is a quantum of gravity related to its field, dubbed the graviton. The existence of this particle would resolve the current inability of the Standard Model to account for this force, as it currently can only account for the other three forces: the problem is that these particles don't interact with matter much (absurd, right?), and thus would be unfeasible to observe with particle detectors (it would require one the size of Jupiter).