Itkin, M., Department of Plant Sciences, Weizmann Institute of Science, Rehovot 76100, Israel, Agricultural Research Organization, The Volcani Center, PO Box 6, Bet Dagan 50250, Israel
Rogachev, I., Department of Plant Sciences, Weizmann Institute of Science, Rehovot 76100, Israel
Alkan, N., Agricultural Research Organization, The Volcani Center, Bet Dagan 50250, Israel, Department of Plant Sciences, Weizmann Institute of Science, PO Box 26, Rehovot 76100, Israel
Rosenberg, T., Department of Plant Pathology and Microbiology, The Hebrew University of Jerusalem, Rehovot 76100, Israel
Malitsky, S., Department of Plant Sciences, Weizmann Institute of Science, Rehovot 76100, Israel
Masini, L., Plant Research International, Wageningen 6700 AA, Netherlands
Meir, S., Department of Plant Sciences, Weizmann Institute of Science, Rehovot 76100, Israel
Iijima, Y., Kazusa DNA Research Institute, Kisarazu 292-0818, Japan, Faculty of Applied Bioscience, Kanagawa Institute of Technology, 1030 Shimo-ogino, Atsugi, Kanagawa 243-0292, Japan
Aoki, K., Kazusa DNA Research Institute, Kisarazu 292-0818, Japan
de Vos, R., Plant Research International, Wageningen 6700 AA, Netherlands
Prusky, D., Agricultural Research Organization, The Volcani Center, Bet Dagan 50250, Israel
Burdman, S., Department of Plant Pathology and Microbiology, The Hebrew University of Jerusalem, Rehovot 76100, Israel
Beekwilder, J., Plant Research International, Wageningen 6700 AA, Netherlands
Aharoni, A., Department of Plant Sciences, Weizmann Institute of Science, Rehovot 76100, Israel

Steroidal alkaloids (SAs) are triterpene-derived specialized metabolites found in members of the Solanaceae family that provide plants with a chemical barrier against a broad range of pathogens. Their biosynthesis involves the action of glycosyltransferases to form steroidal glycoalkaloids (SGAs). To elucidate the metabolism of SGAs in the Solanaceae family, we examined the tomato (Solanum lycopersicum) GLYCOALKALOID METABOLISM1 (GAME1) gene. Our findings imply that GAME1 is a galactosyltransferase, largely performing glycosylation of the aglycone tomatidine, resulting in SGA production in green tissues. Downregulation of GAME1 resulted in an almost 50% reduction in a-tomatine levels (the major SGA in tomato) and a large increase in its precursors (i.e., tomatidenol and tomatidine). Surprisingly, GAME1-silenced plants displayed growth retardation and severe morphological phenotypes that we suggest occur as a result of altered membrane sterol levels caused by the accumulation of the aglycone tomatidine. Together, these findings highlight the role of GAME1 in the glycosylation of SAs and in reducing the toxicity of SA metabolites to the plant cell. © 2011 American Society of Plant Biologists.