WOOSTER, Ohio -- Do you enjoy big, plump tomatoes? If so, you should give thanks to a gene that arose thousands of years ago as early farmers in South America began domesticating this popular fruit, according to Ohio State University crop scientists.
Esther van der Knaap, a geneticist with the university's College of Food, Agricultural, and Environmental Sciences, led an international research team that discovered and cloned a gene that regulates fruit size in tomato. This is only the second domestication gene involved in fruit size ever cloned in any vegetable or fruit crop.
The discovery was reported Sept. 30 in the Proceedings of the National Academy of Sciences.
"This work represents an important improvement in the understanding of the regulation of fruit size and how domestication played a role in the selection of this gene," said van der Knaap, who is based on the Wooster campus of the Ohio Agricultural Research and Development Center (OARDC), the research arm of the college.
The cloned gene, known as SlKLUH, impacts fruit size by increasing cell layers and delaying ripening. According to van der Knaap, this gene promotes extra cell divisions during the process of fruit development, immediately after fertilization. These extra cell divisions lead to enlarged fruit, while the delay in ripening is likely the result of an extension of the cell division stage.
A majority of the research was conducted by Ohio State postdoctoral researcher Manohar Chakrabarti and Ph.D. student Na Zhang, working in van der Knaap's lab. Other scientists based in the U.S., France and Spain collaborated as well.
The research team also identified a potential regulatory element in the promoter of SlKLUH that is hypothesized to control gene expression. The promoter is a region of DNA that is responsible for initiating the transcription of a gene.
"Our findings suggest that the allele giving rise to large fruit arose in the early domesticates of tomato and became progressively more abundant upon further selections," van der Knaap said.
Domestication of crop plants some 10,000 years ago had a significant effect on the development of humans and their societies. However, even today scientists know little about the molecular mechanisms involved in changes in fruit appearance — size, shape and other factors — as a result of domestication and selection by early farmers.
"Despite the importance of fruit mass in the evolution of fruit and vegetable plants, cloning of domestication genes of fruit and vegetable crops has lagged behind that of cereal crops," van der Knaap said. "For that reason, insights into the molecular mechanisms that led to the transition of the fruit from small to large remain mostly unknown."
The cloning of SlKLUH is expected to increase scientists' understanding of fruit development processes, not only in tomato but in other crop species as well.
"We show in this paper that the same gene may have been selected during domestication of chili pepper, leading to increased fruit size in this vegetable crop as well," van der Knaap said.
In 2008, van der Knaap reported the discovery of a gene that controls fruit shape in the journal Science.
This basic research also has important implications for vegetable and fruit production, as it could allow breeders to manipulate genes to create new varieties with desired size and shape characteristics.