Involved in a dynamic process of vesicle-mediated thylakoid membrane biogenesis. Required for the normal organization of vesicles into mature thylakoid stacks and ultimately for leaf development. Also involved in a sugar-signaling mechanism in roots by mediating signaling between the plasma membrane and the plastid. Probably acts downstream of the plasma membrane-delimited heterotrimeric G-protein GPA1 in a D-glucose signaling pathway. Interacts with GPA1. Ubiquitous. Present at higher level in hypocotyls (at protein level). Ubiquitously expressed in all organs, in roots of both light-grown and dark-grown seedlings. Highly expressed in the root apical meristems. Rapidly degraded upon D-glucose but not L-glucose treatment (at protein level). Accumulates in leaves of plants grown under normal long daylight (16 hours)/dark (8 hours) conditions. Levels are greatly reduced in leaves from plants placed in complete darkness for 24 hours. Transcript levels return to normal within 6 hours after plants are returned to normal light levels. Belongs to the THF1 family.