Precisely how tomatoes became large, fat and juicy is a story with chapters covering thousands of years, say scientists who have mapped the complete genomes of both the Heinz variety -- famous in ketchup -- and its tiny Peruvian kin.
Plant geneticist Zach Lippman of Cold Spring Harbor Laboratory with members of the Tomato Genomics Consortium found that tomatoes have 35,000 genes crammed onto only 12 chromosomes.
Humans, seemingly far more complex than a tomato, were initially thought to have about the same number -- 35,000 genes spread over 46 chromosomes. But scientists a few years ago reduced that estimate to a mere 25,000 genes in the entire human genetic dowry.
The goal was to find how the Heinz variety compared genetically to its nearest and oldest wild ancestor. "Comparing the wild tomato genome with the Heinz genome allowed us to explore how the domesticated variety has changed since our ancestors began to select and breed these plants thousands of years ago," Lippman said.
And what's intriguing, he added Monday, is that tomatoes have undergone very little genetic change, even after domestication pumped up their size from a small fruit to the common Heinz 1706 variety, an ingredient in salads and other recipes worldwide.
"We found that there are also approximately 35,000 genes in the wild tomato, too," Lippman said of a tiny, penny-sized Peruvian fruit that has remained largely unchanged genetically over the past 10,000 years.
The diminutive fruit is the closest cousin to the tomato's evolutionary ancestor, which originated in South America millions of years ago. The modern-day variety, known as a currant tomato, is routinely sold on eBay, he said.
The tomato consortium, a global cooperative of plant scientists in 14 countries, has been trying to coax heretofore unknown genetic information from tomatoes for years. What they've learned will help commercial and backyard growers ultimately breed better tomatoes, according to the consortium's research analysis, reported in the current edition of the journal Nature.
Scores of the genes pinpointed in the new genomic investigation contribute the basic DNA that gives tomatoes some of their most appealing traits: taste, texture and size.