@pwgrimes and @chris47 - Just thought I would add my two cents to your discussion with a couple of references that may be helpful. I think you both have a point.

Re: Rice and corn do not have gluten --- The Nutrition Source - What is Gluten: https://www.hsph.harvard.edu/nutritionsource/gluten/

Re: Corn gluten --- "Corn gluten, the by-product of corn processing, contains proteins that inhibit root growth during seed germination for a number of small-seeded annual and ..." --- Corn Gluten Meal: The do’s and don’ts: https://midwestgrowsgreen.org/corn-gluten-meal-the-dos-and-donts/