Gluons also interact gravitationally, like anything with energy. So would any other hypothetical particle, since it would have to have energy to exist at all.
I said earlier in the post "there's one interaction between ALL of the particles that is missing: gravity", so it was implied. Perhaps I should have made that a little clearer.
Two things, greatly oversimplified: 1) all forms of energy (including mass) are sources for gravity. 2) Interaction with the Higgs gives rise to what we observe as mass of particles; without this interaction, we'd have massless particle, with essentially the same energy, but moving at the speed of light. The net gravitational effect would be very different from what we observe though...