GPT2,a glucose 6-phosphate/phosphate translocator, plays an important role in environmental sensing in mature leaves of Arabidopsis thaliana, and its expression has also been detected in arabidopsisseeds and seedlings. Dyson et al. study wild-type A. thaliana and a gpt2 T-DNA insertion knockout line, and find that plants lacking GPT2 expression are delayed in seedling establishment, specifically in the process of cotyledon greening (rather than germination). This phenotype cannot be rescued by glucose in the growth medium, with greening being hypersensitive to glucose. Germination itself is, however, hyposensitive to glucose in the gpt2 mutant. They conclude that endogenous sugar signals function in controlling germination and the transition from heterotrophic to autotrophic growth, and that the partitioning of glucose 6-phosphate, or related metabolites, between the cytosol and the plastid modulates these developmental responses.