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MOLECULAR MAPPING OF THE LAZY-2 GRAVITROPIC RESPONSE GENE OF TOMATO.   J. Well, A. Madlung, K. Krutovskii R. Meyer, TJ White, and T.L. Lomax. Dept. of Botany and Plant Pathology, Oregon State University, Corvallis OR 97331-2902

Shoots of the single gene lazy-2 (lz-2) mutant of tomato exhibit a reversed gravitropic response in the presence of red light. Our laboratory has previously shown this phenotype to be regulated by the red light photoreceptor, phytochrome (Gaiser, J.C. and Lomax, T.L. 1993.Plant Physiol. 102: 339-344). Isolation of the corresponding gene would provide a unique opportunity to elucidate the mechanism by which light and gravity interact to regulate plant architecture. We are attempting to isolate the Lz-2 gene using a map-based cloning strategy. Using a mapping population generated by crossing the lz-2 mutant in Lycopersicon esculentum (domestic tomato) with  L. pennellii (a wild tomato relative), we have localized the Lz-2 gene to the centromeric region of chromosome 5 in tomato (Behringer, F.J. and T.L. Lomax 1999. J. Heredity 90: 489-493). Proximity to the centromere complicates mapping due to reduced recombination, therefore we have generated a new backcross mapping population using L. pimpinellifolium, a more closely-related wild tomato species. Here, we report the results of screening that population with molecular markers that are closely liked with the Lz-2 gene. In a parallel approach to identifying the Lz-2 gene, we are also using transposon tagging with an Ac/Ds transposon insertion that is closely linked to the Lz-2 locus. Analysis of the tagged progeny for the lazy-2 mutant phenotype will be described. 

(Supported by NASA NAG2-1341 and a Howard Hughes Medical Institute Undergraduate Summer Research fellowship to J.W.)