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Insight From an ‘Inside-out Fruit’

Strawberries’ External Seeds Helped UMD Researcher ID Mechanism for Fruit and Seed Development in Flowering Plants

By Georgia Jiang

closeup of strawberries in boxes

Focusing on strawberries, UMD researchers discovered how fertilization—or pollination—triggers a flowering plant to start the fruit development process.

Raghavendra Mithare/Unsplash

As global temperatures rise and populations of bees and other pollinators dwindle, food crop production is increasingly becoming a puzzle for growers.

A new study by researchers at the University of Maryland puts some of the pieces together, providing insight into exactly how flowering plants develop fruits and seeds.

“Understanding this process is especially important because common food crops—such as peanuts, corn, rice and strawberries—are all fruits and seeds derived from flowers,” said Zhongchi Liu, the study’s senior author and a professor in the Department of Cell Biology and Molecular Genetics and affiliate professor in the Department of Plant Sciences and Landscape Architecture. “Knowing how plants 'decide' to turn part of their flowers into fruit and seed is crucial to agriculture and our food supply.”

Funded by the National Science Foundation, the study was published last month in the journal Nature Communications. Liu and her team aimed to discover how fertilization—or pollination—triggers a flowering plant to start the fruit development process. The team suspected that an internal communication system was responsible for signaling the plant to develop fruit, but the researchers were unsure how that system was being activated by fertilization or pollination.

To find out, the team simulated pollination and fruit development mechanisms using strawberry plants. Strawberries are particularly suited to fertilization modeling due to their unique structure and seed location.

“As an ‘inside-out’ fruit, strawberry seeds are much easier to manipulate and observe than the seeds of other fruits like tomatoes,” Liu said. “This made it easier for us to view the seeds and extract genetic information from them at multiple stages of plant development.”

Liu and her team identified AGL62, a gene universally found in all flowering plants, as the trigger to a plant’s production of fruit and seed.

AGL62 stimulates the production of an essential plant growth hormone called auxin. Once the gene activates, auxin is synthesized to prompt the creation of seedcoat, the outer protective layer of a seed; the endosperm, the part of a seed that provides food for a developing plant embryo; and fruit. Auxin’s role in regulating endosperm growth is especially significant for researchers as it impacts the size of the grain and enlargement of the fruit.

“Auxin levels can limit how big an endosperm can grow and how much nutrition endosperm can accumulate for a plant embryo,” Liu said. “More auxin can boost grain size and stimulate fruit enlargement. When there’s less auxin, endosperms are unable to feed plant embryos properly and we end up with lowered crop productivity—smaller or deformed fruits that aren’t commercially viable.”

Gerald Schoenknecht, a program director in NSF’s Division of Integrative Organismal Systems, added, “Strawberry fruits are textbook examples of how the plant hormone auxin produced in seeds controls fruit size. Discovering a gene that is required for auxin synthesis after fertilization may open avenues to achieve fruit development without fertilization.”

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