Aha--I see from other discussions that "te gusta" in this context means "pleasing to you" rather than "you like" per se; the question is really asking "Is rice not pleasing to you?" So it uses the indirect object form "te" rather than the subject form "tú". (http://studyspanish.com/lessons/gustar.htm)
It's not gusta, it's gusta (singular) or gustan (plural) because the thing performing the action (el arroz in your example) comes after the verb here, gustar is not actually to like, it is to please, therefore "Te gusta el arroz?" is "Does the rice please you?" It would only be gustas if something liked you, or rather you pleased something, as in "Me gustas tu" <-tu should have accent. That's "you please me".