The evolution of sugar signalling in the green lineage

Sugars are not only central metabolites in plants but also act as signalling molecules that coordinate growth, development, and physiology. In the green lineage (viridiplantae), the intermediate of trehalose biosynthesis, trehalose 6-phosphate (Tre6P), has emerged as a central regulator of carbon status. In angiosperms, Tre6P signalling is integrated with energy-sensing mediated by kinases such as SnRK1 and TOR to balance growth with metabolism and environmental factors. Here we review the current knowledge on the functions of sugar signalling components in the green lineage. We put a special emphasis on Tre6P signalling as genomic, transcriptomic, and metabolomic studies across algae, bryophytes, and vascular plants indicate that Tre6P's role as a sugar signal predates the colonization of land and may have been instrumental during terrestrialization and the evolution of vascular systems. Functional studies in mosses, and angiosperms reveal conserved roles of Tre6P in vegetative growth, and the initiation of sexual reproduction, underscoring its potential as a conserved signalling metabolite. Taken together, these insights support the view that Tre6P has acted as a conserved and adaptable hub linking carbon availability to plant development and reproduction throughout plant evolution.