Regulation of Inflorescence and Pedicel Development in Tomato.

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The shoot meristem of flowering plants is a multicellular organ that provides the capacity for indeterminate growth of the shoot. The research team will investigate how the cells in the shoot meristem and its derivative organs are coordinated during development by continuing our study of the jointless-1 mutation of tomato. In jointless-1 mutants, the inflorescences revert to vegetative growth after forming only one or two flowers and terminate with a vigorous, leafy shoot. jointless-1 mutants also form flower pedicels that completely lack an abscission zone. Thus, the JOINTLESS-1 gene of tomato is involved in two important developmental processes, the maintenance of the inflorescence meristem state and the formation of the pedicel abscission zone. By analyzing periclinal chimeras it was found that internal (L3) cells of the meristem control both inflorescence meristem determinacy and pedicel abscission zone formation. Cloning of JOINTLESS-1 revealed that it is a MADS box gene. The investigations of coordination of cells during the processes of maintaining the inflorescence meristem and development of pedicel abscission zones will be continued. 1. In situ hybridization will be performed using JOINTLESS-1 probes on wild-type and jointless-1 mutants and on the six periclinal chimeras to learn more about the nature of the cell coordination that occurs during inflorescence development and abscission zone formation. 2. Patterns of JOINTLESS-1 expression will be examined in various mutants that we have found to show genetic interactions with jointless-1 from double mutant analysis. Such studies will provide a clearer understanding of the interactions of these genes that result in different types of meristem activity. 3. Sets of periclinal chimeras will be constructed between wild-type plants and macrocalyx, another mutation that affects both abscission zone development and inflorescence meristem maintenance, and between macrocalyx and jointless-1. The hypothesis that macrocalyx is involved in the reception of the signal produced by L3 cells that are wild-type for the JOINTLESS -1 gene will be tested. 4. A lineage analysis will be identified for the developing pedicel to determine the patterns of cell divisions that give rise to the various regions of this organ (proximal pedicel, abscission zone, and distal pedicel) in wild-type and jointless-1 mutant plants. With these experiments more should be learned about the cellular and genetic interactions regulating abscission zone formation and inflorescence development to elucidate the relationship between these two developmentally interesting and agriculturally important processes.