In Arabidopsis, the onset of the adult phase is characterized by the appearance of hairs on the lower surface of the leaf and a change in leaf shape from round leaves with smooth edges to elongated leaves with serrated edges. The juvenile-to-adult transition, or vegetative phase change, is controlled by the activity of microRNA-156. The predominant genes encoding this miRNA—MIR156A and MIR156C—are transcribed to produce primary mRNA transcripts (pri-miR156 A/C), which are further processed to generate mature transcripts (miR156). These guide the cleavage of target (SPL) mRNAs, thereby reducing SPL mRNA abundance, which has the effect of preventing vegetative phase change. Sugars regulate the timing of the juvenile-to-adult transition by repressing miR156 accumulation. Early in development, miR156 levels are high, promoting juvenile traits. As the plant matures, miR156 levels steadily decrease (red bar). After germination, plants start to accumulate sugars through photosynthesis and, as they grow older, the overall photosynthetic output of the shoot increases (green bar). Sucrose, the major transportable sugar, moves from the pre-existing leaves to the young leaf primordia (boxed), where its accumulation inhibits the transcription of MIR156A and MIR156C. In the initial steps of glycolysis, sucrose is broken down into glucose, which in turn causes degradation of the miR156 precursors pri-miR156A and C. As a result, miR156 levels decrease and SPL levels increase (blue bar), thereby promoting the expression of adult traits.