Genetic Mechanism to Increase Tomato Production Explained

Zach Lippman (Cold Spring Harbor Laboratory)

Biologists at Cold Spring Harbor Laboratory in New York discovered a genetic process underlying a breeding practice that helps improve yields of tomatoes. The Cold Spring Harbor team led by plant biology professor Zach Lippman, with a colleague from Monash University in Australia, published its findings yesterday in the journal PLoS Genetics.

The team’s research looked at commercial tomato varieties, the kinds used to make tomato juice or canned pasta sauce. These commercial tomatoes grow on plants that more resemble bushes than the familiar vine-style garden plants. While the compact size and structure of tomato bushes work well with mechanical harvesters, their fruit stop growing sooner, which makes the yields smaller. The goal for growers, then, is to increase the yields of these tomato bushes, while maintaining their compact size and shape.

A widely recognized principle among farmers, especially among tomato growers, is that cross-breeding genetically distinct plants generates more robust offspring, but the genetic process underlying this practice continues to be a subject of debate. Lippman and colleagues sought to better understand this process of heterosis, or hybrid vigor, as applied to commercial tomato varieties.

Lippman earlier identified a mutation in the tomato gene resulting from hybrid vigor affecting production of a hormone called florigen that regulates the quantity of flowers on tomato plants. The mutation, in one of two copies of the gene encoding florigen, results in dramatically more tomato fruit on a plant. Thus the current Cold Spring Harbor team sought to explain the way this process works.

The researchers conducted tests of commercial plants grown in controlled greenhouses, where they extracted and analyzed DNA from the plants to identify their particular genomic sequences. The analysis shows the mutation leads to small adjustments in florigen levels that cause the young tomato plants to delay and reduce the production of flowers. These reductions in florigen and smaller quantity of flowers make it possible for tomato plants to increase their number of fruit.

Identifying this process, especially the relationship between florigen levels and tomato yields, says Lippman in a Cold Spring Harbor statement, suggests “that it may be possible to tweak florigen levels to increase yields even further.” The researchers conducted an early test of the concept with Arabidopsis, a model plant related to crops like broccoli and cauliflower, and found similar one-copy mutations could change the flowering of the plant, but not necessarily its yields. These results, say the team, suggest fine-tuning florigen levels may need to be considered one species at a time.

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