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Thursday, October 28, 2021

Mismatched genes

According to the California Tomato Growers Association, the average American eats almost 80 pounds of tomatoes annually. California generates almost half of the world’s processed tomatoes, while China produces nearly 30.9 million metric tons, or 25 percent of global tomato production.

But tomato lovers might not know that commercially-grown tomatoes could be tastier, more disease resistant and more abundant and accessible with the transfer of a specific gene or genes from a wild species of tomato.

The trick is in getting the genes to mix.

Roger Chetelat, director and curator of UC Davis’ Charles M. Rick Tomato Genetics Resource Center, and Wentao Li, a postdoctoral researcher in the department of plant sciences, recently identified a tomato-pollen gene that plays a role in blocking cross-species fertilization. This discovery may be evidence that there are mechanisms that underlie the rejection of a plant’s own pollen as well as foreign pollen from another species.

Similar to the dangers of closely related humans reproducing, inbreeding between closely related or identical species of plants, like tomatoes, which might carry both a similar disadvantageous gene, can lead to the expression of harmful mutations in offspring. Such mutations often cause infertility and inability to cope with harsh or changing environmental conditions.

Breeding with unrelated species can be equally dangerous for the plant.

“Species generally in nature avoid hybridization because it breaks down the species themselves,” said Chetelat. “Genes between species often expresses deleterious [harmful] traits.”

The identified gene by Chetelat and Li is related to both the prevention of self-fertilization and the prevention of hybridization, including crosses between wild-type and cultivated-type tomato species.

Through identifying this gene, plant scientists are one step closer to understanding and manipulating the reproductive barriers that might help them access desired traits found in wild tomatoes.

“In many species, especially true in tomatoes, variation from wild relatives is often useful to breeders,” said Jeffrey Ross-Ibarra, UC Davis assistant professor of plant sciences. “Wild relatives are often resistant to things, and we want to bring those useful genes into the cultivated plant.”

In the wild, the rejection of foreign pollen stops constant hybridization. But modern plant scientists wish they could go around the reject gene to create a heartier plant.

“Figuring out the genetic basis of why you can’t cross the two plants is a big step forward,” Ross-Ibarra said.

Dina St. Clair, UC Davis professor of vegetable crops, commented on the greater significance of this discovery.

“So why would people care about this, why should they care about this? We have more and more people on the earth, and we have more people to feed and we need to feed more people with less water and fertilizers,” St. Clair said.

For many plant scientists, genetics is a matter of combating world hunger.

“If we can tap into wild species to help us better utilize valuable genes for many important traits including pest tolerance, drought tolerance and to build better crop plants that yield more food with less inputs, we are collectively contributing to the population,” St. Clair said.

CAMMIE ROLLE can be reached at science@theaggie.org.

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