Final Activity Report Summary - GINO (Gibberellins in Tomato Ovule Development) After pollination and fertilisation tomato ovary develops into a fruit, via a process which is mediated by the plant hormone gibberellin (GA). Application of GA to the outside of the ovary induces fruit growth even when pollination and fertilisation do not take place. The role of plant hormones in the mechanism that regulates fruit set is not well understood. We discovered that the activity of many genes involved in abscisic acid (ABA), auxin and plant hormones signalling were directly modulated after fertilisation or GA treatment in ovaries, which was the tissue that formed the fruit after fertilisation. The results suggested that fertilisation did not only stimulate fruit set via GA biosynthesis. GA probably acted together with auxin and ABA. ABA regulated dormancy in seeds and axillary buds. We hypothesised that fruit set was regulated by a balance of hormones; on the one hand GA and auxin that stimulated growth, and on the other hand ABA that induced dormancy and prevented fruit growth prior to fertilisation. These results were also important for the understanding of the regulation of developmental processes by hormones in general. The mechanism and importance of the hormone balance in fruit set was further investigated by the time of the project completion through modulation of the activity of some of the identified genes by generating transgenic tomato plants. Preliminary results suggested that these genes played important roles during fruit set as some transgenic tomato lines produced seedless fruits.
