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Origins of the Massive Beefsteak Tomato Discovered by Scientists

First Posted: May 26, 2015 08:06 AM EDT

As summer approaches, tomatoes ripen on the vine. One of the most popular breeds of these tomatoes are beefsteak tomatoes and now, scientists may have discovered their origins. They've identified a set of genes that control stem cell production in the tomato, and mutations in these genes explain how the mammoth beefsteak tomato was first created.

In its original, wild form, the tomato plant produces tiny, berry-sized fruits. Obviously, tomatoes have come a long way since then. In fact, the first tomatoes brought to Europe from Mexico by the conquistador, Hernan Cortez, were the huge beefsteaks. Only now, though, have researchers found out how these massive tomatoes first came to be.

Apparently, it has to do with the number of stem cells in the plant's growing tip, called the meristem. More specifically, the researchers traced an abnormal proliferation of stem cells to naturally occurring mutations that arose hundreds of years ago in a gene called CLAVATA3. Selection for this rare mutant by plant cultivators is the reason we have beefsteak tomatoes today.

CLAVATA genes actually inhibit stem cell production. Several genes in the CLAVATA family encode for receptor proteins that sit on the surface of plant cells, the equivalent of locks, as well as a series of proteins that dock at these receptors, which are the equivalent of key. When a CLAVATA key is made and fits in a CLAVATA lock, a signal is sent inside the cell that tells WUSCHEL to slow down and prevents it from making too many stem cells.

When CLAVATA genes are mutated, though, the plant makes too many stem cells in the meristem. The researchers also found never-before-studied mutant tomato plants, three of which contained faulty genes encoding enzymes that add sugar molecules to proteins. The enzymes, called arabinosyltransfersases (ATs), add sugar molecules called arabinoses to CLAVATA3-one of the CLAVATA keys. These sugars are required to fit a CLAVATA lock.

The findings reveal that there is a continuum of growth possibilities in the tomato plant. By adjusting the number of sugars on CLAVATA keys and through other mutations affecting components of the pathway, it's possible to fine-tune growth in ways that may allow breeders to customize fruit size.

The findings are published in the journal Nature Genetics.

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