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A fruit is an angiosperm structure developing from a flower's ovary, sometimes together with additional floral tissues. Its enclosing wall, the pericarp, develops from the ovary wall; a seed develops from an ovule. A fruit and a seed therefore represent different structures, even when they are closely attached.

A tomato is a fruit in this anatomical sense regardless of its culinary classification. Fertilization usually initiates coordinated seed and fruit development, but parthenocarpy produces fruits without fertilization. Tomato experiments manipulating auxin and gibberellin signaling separated the control of fruit initiation from the presence of developing seeds, illustrating why a fruit need not contain mature seeds.^[ref]

Jianhong Hu is a plant researcher credited as first author of a 2018 study connecting auxin and gibberellin signalling during tomato fruit initiation. The paper lists a Department of Biology affiliation at Duke University.

Hu and colleagues combined protein-protein interaction assays with single and double mutants. They found interactions between DELLA repressors and auxin-response regulators, and additive effects on parthenocarpy. The combination of biochemical interaction and whole-plant phenotypes linked molecular signalling to whether an unfertilized ovary begins growing into a fruit.^[ref]

Parthenocarpy is fruit development without fertilization. Because no fertilized ovule is needed to initiate the fruit, it can produce a seedless fruit. It is distinct from apomixis, which produces an embryo or seed without the usual sexual process: a seedless fruit and an asexually formed seed solve different biological problems.

In tomato, increased auxin or gibberellin signalling can trigger parthenocarpy. Experiments with single and combined mutations affecting the two signalling systems separated the growth programme of the ovary from the usual requirement for fertilization. This makes parthenocarpy a useful test of how reproductive development is initiated.^[ref]