Researchers identify a genetic mechanism that coordinates flower development and fruit formation, paving the way toward tomato varieties with more reliable winter harvests.

Every tomato begins with a flower. But before a fruit can grow, an intricate sequence of events must happen in perfect order. The flower's male and female organs must develop together, pollen must be released at exactly the right time, and fertilization must occur.

Many things can disrupt this delicate process, including genetic changes and environmental stress. Temperature extremes are a major challenge: cold can reduce pollen viability and prevent fertilization, while previous research has shown that heat can also interfere with fruit set.

Now, researchers have uncovered a genetic system that keeps this process synchronized. Their findings could eventually help scientists develop tomato varieties that produce fruit more reliably during challenging growing conditions, including colder seasons.

The study was led by Prof. Naomi Ori and doctoral researcher Nave Man Hebrew University, in collaboration with researchers from the Leibniz Institute of Plant Biochemistry in Germany and Israel's Agricultural Research Organization (Volcani Institute).

The team focused on a system involved in the plant's response to auxin, an important plant hormone that regulates growth and reproduction. Within this system, some factors promote the response while a tiny regulatory RNA called miR167 acts as a brake, helping keep the activity of key genes in balance.

Using CRISPR gene-editing technology, the researchers altered several of these genes to understand how they influence flower development and fruit production.

They discovered that two closely related genes, SlARF8A and SlARF8B, work together to coordinate the development of the flower's male and female reproductive organs. One of the genes also helps control when the flower's anthers open to release pollen—a critical step for successful fertilization.

By changing both the promoting and restraining sides of this genetic balancing system, the researchers uncovered one combination with an especially interesting result.

The gene-edited plants were able to begin developing fruit without fertilization, a natural process known as parthenocarpy, which produces seedless tomatoes. These plants began producing fruit earlier under all tested conditions. Under cold winter conditions, they were able to produce fruit when the other tomato plants produced little or none.

In winter greenhouse experiments, the gene-edited plants produced more than 18 times as many fruits as the regular plants early in the growing season. By harvest, they yielded six times more ripe tomatoes and ten times the total weight of ripe fruit.

While most tomatoes on the modified plants had already ripened and turned red by the end of the experiment, the majority of fruit on the unmodified plants remained green.

The gene-edited plants were also more compact, directing more of their energy toward producing fruit rather than stems and leaves.

"Our findings show how tomato plants use a carefully balanced genetic system to coordinate flower development, pollen release and the beginning of fruit growth," said Prof. Ori. "Understanding this system may eventually help us develop crops that produce fruit more reliably when temperatures make normal fertilization difficult."

The researchers say the findings could ultimately help extend tomato production into colder months and improve the stability of winter harvests.
Before the approach can be used commercially, further studies will be needed to determine how these genetic changes affect fruit size, flavor and overall quality, and whether they can be successfully introduced into agricultural varieties.

The discovery may be especially valuable for tomatoes grown for processing, where seedless fruit and reduced jelly content can be advantageous.
The research was supported by the German Research Foundation, the Israel Science Foundation, and the Israeli Ministry of Agriculture.