Gene splicing aims to increase starch production in tomatoes.

Three Ohio researchers are designing and growing a beefier tomato for the processing industry. Their project could save processors in the U.S. $75 million annually. The technology also has implications for worldwide food and fuel production, they believe. The researchers are using recombinant gene technology to boost starch production in the tomato as well as decrease a natural loss of starch that occurs as plants mature. Right now, they are trying to grow plants and plan trials in about a year.

Tomatoes grown for the processing market usually contain 95% water. If that could be reduced by just 5% or 6%, manufacturers of ketchup, tomato paste and soup could save processing costs. Plant biologists have tried to increase the solids content by using traditional plant-breeding methods, but the yield of the tomato plants has always decreased.

The Ohio scientists will increase starch production by amplifying the activity of one gene. They will decrease the breakdown of starch by depressing the activity of another gene. They expect to confirm the genetic alterations in starter plants and eventually transplant them into soil.

The amount of starch in a tomato fruit totals 20% in the early stages of maturation, but the accumulation is fleeting. As the fruit ripens, the starch mobilizes and is converted to sugars. Previous studies show that plants that produce more starch in the unripe stages have a higher solids content in the ripe stages. The researchers will insert a modified enzyme (Escherichia coli ADP glucose pyrophosphorylase) into the plant genes to try and boost production of starch.

The researchers will decrease starch loss by altering another gene in the plant. Scientists have identified the protein involved. Inhibiting its activity stops the breakdown of starch. They have mapped the DNA sequence of the glucose translocator gene, which controls starch degradation, in spinach. For this project, investigators will use a mutant of the plant Arabidopsis that is thought to be missing this translocator and so is unable to break down starch.

The mutant form of the plant contains 500% more starch than is present in the non-mutant plant. Researchers will identify the same translocator gene in the tomato and replace it with the mutated gene. They use bacteria that normally infects plants. They cut the bacteria's DNA and put their gene of interest in that spot, then put it back together and introduce it back into the bacteria. The bacteria infect the plant, and the plant and all of its progeny will carry that altered gene.

The translocator protein is like a door that allows glucose to move out of the amyloplast. Scientists want to shut that door, and this mutation does that. It might work for tomatoes and any other plant that stores starch.

Further information. Jerome Servaites, University of Dayton, Department of Biology, 300 College Park, Dayton, OH 45469; phone: [phone]; fax: [phone]; email: [e-mail].