The trehalose-6-phosphate synthase AtTPS I is involved in regulating sugar metabolism and partitioning in connection with plant morphogenesis and development in an as yet unknown fashion. AtTPS I expressed in yeast supports the synthesis of trehalose as well as an essential regulatory function in glucose consumption. The gene is essential for embryo development in Arabidopsis and its overproduction leads to sugar insensitivity as well as increased drought tolerance. Here we report on AtTPS I protein containing complexes in Arabidopsis and in yeast. AtTPS I co-migrated in FPLC separated extracts with 600-800 kDa protein complexes containing the cell cycle kinase CDKA; I and tubulin. In two hybrid experiments, the N-terminal domain of AtTPS I interacted with CDKA; I and the CDKA; I interacting kinesin KCA 1. In vitro precipitation tests using CDKA; I affinity beads showed that AtTPS 1 co-precipitated with KCA 1 and tubulin. This protein complex was predominantly observed in inflorescence tissue. The data presented suggest that trehalose metabolism impinges on the cell cycle regulation through a close communication with the cell cycle dependent kinase CDKA;l and the kinesin KCAL (c) 2007 Elsevier Ireland Ltd. All rights reserved.