To explore these processes in the tomato plant, Chetelat and Li set out to locate the chromosomal regions harboring genes that control fertilization and can cause a plant’s flower to reject pollen from other species. The researchers identified a gene expressed in pollen known as a “Cullin1” gene, which interacts genetically with a gene at or near the S-locus to block cross-species pollination.

They found that a mutant (inactive) form of the Cullin1 protein is present in cultivated tomato, as well as in related red- and orange-fruited wild tomato species, all of which are capable of being fertilized by their own pollen. However in the green-fruited tomato species, most of which block self-pollination, the Cullin1 protein is functional.

In short, their findings suggest that the Cullin1 protein is part of a biochemical gatekeeper: An active form of the protein is required for pollen to fertilize plants of another species, if that species is capable of rejecting its own pollen.

While these findings are from a study of tomato hybrids, the researchers suspect that they will be relevant to other members of the Solanaceae family, which also includes potatoes, chili peppers and eggplant.

Chetelat and Li are members of the multicenter Interspecific Reproductive Barriers in Tomato research group. This consortium of six laboratories throughout the United States is investigating how tomato plants block cross-species pollination, in order to provide the scientific community with tools for better understanding reproductive biology. More information about the research group is available at http://irbtomato.org.

More information about the Charles M. Rick Tomato Genetics Resource Center is available at http://tgrc.ucdavis.edu.

Funding for this study was provided by the National Science Foundation’s Plant Genome Program.