The tomato MADS box gene no. 5 (TM5) is shown here to be expressed in meristematic domains fated to form the three inner whorls-petals, stamens, and gynoecia-of the tomato flower. TM5 is also expressed during organogenesis and in the respective mature organs of these three whorls. This is unlike the major organ identity genes of the MADS box family from Antirrhinum and Arabidopsis, which function in overlapping primordial territories consisting of only two floral whorls each. The developmental relevance of the unique expression pattern of this putative homeotic gene was examined in transgenic plants. In agreement with the expression patterns, antisense RNA of the TM5 gene conferred both early and late alterations of morphogenetic markers. Early defects consist of additional whorls or of a wrong number of organs per whorl. Late, organ-specific changes include evergreen, cauline, and unabscised petals; green, dialytic, and sterile anthers; and sterile carpels and defective styles on which glandular trichomes characteristic of sepals and petals are ectopically formed. However, a complete homeotic transformation of either organ was not observed. The early and late floral phenotypes of TM5 antisense plants suggest that TM5 mediates two unrelated secondary regulatory systems. One system is the early function of the floral meristem identity genes, and the other system is the function of the major floral organ identity genes.
To understand the details of the homeotic systems that govern flower development in tomato and to establish the ground rules for the judicious manipulation of this floral system, we have isolated the tomato AGAMOUS gene, designated TAGí, and examined its developmental role in antisense and sense transgenic plants. The AGAMOUS gene of Arabidopsis is necessary for the proper development of stamens and carpels and the prevention of indeterminate growth of the floral meristem. Early in flower development, TAGí RNA accumulates uniformly in the cells fated to differentiate into stamens and carpels and later becomes restricted to specific cell types within these organs. Transgenic plants that express TAGí antisense RNA display homeotic conversion of third whorl stamens into petaloid organs and the replacement of fourth whorl carpels with pseudocarpels bearing indeterminate floral meristems with nested perianth flowers. A complementary phenotype was observed in transgenic plants expressing the TAGl sense RNA in that first whorl sepals were converted into mature pericarpic leaves and sterile stamens replaced the second whorl petals.
To understand the details of the homeotic systems that govern flower development in tomato and to establish the ground rules for the judicious manipulation of this floral system, we have isolated the tomato AGAMOUS gene, designated TAG1, and examined its developmental role in antisense and sense transgenic plants. The AGAMOUS gene of Arabidopsis is necessary for the proper development of stamens and carpels and the prevention of indeterminate growth of the floral meristem. Early in flower development, TAG1 RNA accumulates uniformly in the cells fated to differentiate into stamens and carpels and later becomes restricted to specific cell types within these organs. Transgenic plants that express TAG1 antisense RNA display homeotic conversion of third whorl stamens into petaloid organs and the replacement of fourth whorl carpels with pseudocarpels bearing indeterminate floral meristems with nested perianth flowers. A complementary phenotype was observed in transgenic plants expressing the TAG1 sense RNA in that first whorl sepals were converted into mature pericarpic leaves and sterile stamens replaced the second whorl petals.
Divergent architecture of shoot models in flowering plants reflects the pattern of production of vegetative and reproductive organs from the apical meristem. The SELF-PRUNING (SP) gene of tomato is a member of a novel CETS family of regulatory genes (CEN, TFL1, and FT) that controls this process. We have identified and describe here several proteins that interact with SP (SIPs) and with its homologs from other species: a NIMA-like kinase (SPAK), a bZIP factor, a novel 10-kD protein, and 14-3-3 isoforms. SPAK, by analogy with Raf1, has two potential binding sites for 14-3-3 proteins, one of which is shared with SP. Surprisingly, overexpression of 14-3-3 proteins partially ameliorates the effect of the sp mutation. Analysis of the binding potential of chosen mutant SP variants, in relation to conformational features known to be conserved in this new family of regulatory proteins, suggests that associations with other proteins are required for the biological function of SP and that ligand binding and protein-protein association domains of SP may be separated. We suggest that CETS genes encode a family of modulator proteins with the potential to interact with a variety of signaling proteins in a manner analogous to that of 14-3-3 proteins.
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