The paper proposes annotation guidelines for syntactic dependencies that span across speaker turns -including collaborative coconstructions proper, wh-question answers, and backchannels -in spoken language treebanks within the Universal Dependencies framework.Two representations are proposed: a speaker-based representation following the segmentation into speech turns, and a dependency-based representation with dependencies across speech turns.New propositions are also put forward to distinguish between reformulations and repairs, and to promote elements in unfinished phrases.