Fruit development

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Fruit development

Strawberries, apples, pears, bananas, but also cucumbers, tomatoes, peppers, and pumpkins, are all fruits. All protecting their seeds and distributing them. Because we, and animals are picking them, taking, and eating them. There are also countless seedless fruits. Bred specially for us. But we actually don’t know how this is possible.

The development of seed and fruit all starts at the moment of fertilization. In contrast to the single fertilization that takes place by people and the animals around us, flowering plants have a double fertilization. The first fertilisation is the well-known union of egg and the sperm cells, resulting in a developing embryo.

The second fertilization is the union of a second sperm cell with the two nuclei of the central cell, resulting in the development of the endosperm. Of the endosperm it was long thought that it purely functions as a nutrient reserve for the future seed. But recent research indicates it also has a role in the coordination of embryo, seed coat and fruit development. Afterall, it is useful if this all occurs more or less synchronized.

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Not the seed production, but endosperm development is essential for our fruits

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American researchers studied in strawberries how the endosperm initiates fruit development. They analysed why a mutant did not develop any fruit, even though it was double fertilised. Firstly, they compared the genes that were turned on or off in the mutant strawberry plants with those in normal strawberry plants. It turned out that in the mutant the genes for the production of the plant hormones auxin and gibberellic acid were turned off. Auxin or gibberellic acid application to the mutant strawberry could indeed start off fruit production.

The auxin needed, so notice the researchers subsequently, was not produces by the embryo but by the endosperm. Directly after fertilization, auxin production by the endosperm starts. The produced auxin in turn stimulates fruit development. When the auxin production does not start, fruit will not form. This did not only was the case for strawberries, but also in the model plant Arabidopsis, (tale cress), and probably also for other flowering plants.

Not the seed production, but endosperm development is essential for our fruits. This not only explains why the mutants hardly developed any fruit, but it can also explain how seedless fruits are possible. It is after all entirely possible to have a mutation that starts the production of auxin and gibberellic acid without fertilization.

Literature

Guo L., Luo X., Li M., Joldersma D., Plunkert M., Liu Z. (2022) Mechanism of fertilization-induced auxin synthesis in the endosperm for seed and fruit development. Nature Communications 13, 3985  https://doi.org/10.1038/s41467-022-31656-y