Involved in the biosynthesis of the siderophore pseudomonine. Specifically adenylates L-threonine and loads it onto a peptidyl carrier protein, via a thioester linkage to the phosphopanthetheine moiety (PubMed:18710233). May function in trans to generate substrate-bound PmsG (PubMed:18710233). Activates proteinogenic L-Thr preferentially over L-allo-Thr or D-Thr (PubMed:18710233). ATP + holo-[peptidyl-carrier protein] + L-threonine = AMP + diphosphate + L-threonyl-[peptidyl-carrier protein] Siderophore biosynthesis; pseudomonine biosynthesis. Belongs to the ATP-dependent AMP-binding enzyme family.