Figure 6

Working model of phase change regulation by FUS3. During late embryogenesis and early germination, FUS3 negatively influences a number of factors, including ethylene signaling. As a consequence, the EIN3 protein, a key positive regulator of ethylene signaling, is reduced, thereby causing a decrease in the expression of downstream transcription factors such as ERFs and EDFs. A reduction of these ethylene-dependent transcription factors prevents the premature transition from the juvenile to the adult phase of development. In the loss-of-function fus3 mutant, ethylene signaling increases, which in turn accelerates vegetative phase transitions. The lack of full restoration of altered gene expression by ethylene inhibitors and the observation that only a subset of ethylene responsive genes are affected by FUS3 also suggest that FUS3 may have ethylene-independent effects. Consistent with this hypothesis, many ethylene-responsive genes contain FUS3-binding RY sequences in their promoter elements. It is therefore possible that FUS3 also influences these genes and some aspects of phase transitions through ethylene-independent mechanisms.