Fig. 5.

Model for SlARF7 function in tomato fruit set and development. (A) After pollination, the levels of both auxin and GA increase, resulting in the activation of auxin and GA response genes, which, in turn, will trigger fruit growth by regulating cell division and cell expansion (adapted from De Jong et al., 2009a). However, these pathways do not act independently of each other. Our data suggest that after pollination the auxin response genes stimulate GA biosynthesis through the transcriptional activation of GA 20-oxidases (GA20ox). Furthermore, SlARF7 acts as a negative regulator of the auxin and GA signalling pathways. After fertilization, transcript levels of SlARF7 decrease and both pathways are released from repression. (B) In the RNAi SlARF7 lines, SlARF7 transcript levels are reduced independently of fertilization. This reduction causes the partial activation of the auxin and GA signalling pathways (black), resulting in parthenocarpic fruit growth. Due to the silencing of SlARF7, the pollination- and fertilization-dependent activation of the auxin and GA pathways is bypassed (grey).