Genetical control of flowering in tomato (Lycopersicon esculentum Mill.) : a case study of some key genes regulating flowering time and morphogenesis of reproductive structures

In the present work, we initiated a study of the genetic control of various aspects of the reproductive process in tomato, including the flowering time, the structure of the inflorescence and some floral traits. We investigated 5 mutants known to be affected in their flowering response: uniflora (uf), blind (bl), compound inflorescence (s), single flower truss (sft) and jointless (j). For most of these mutant plants, both the flowering time and the reproductive structure were altered. The recording of their flowering time phenotype suggested that UF, BL, SFT and to a lesser extent J and S are flowering promoters. Regarding the initiation of the reproductive structures, UF may participate in the identity of the inflorescence meristem; BL, J and SFT most likely control the maintenance of the inflorescence meristem and S appears to be a floral meristem identity gene. The uf:s, uf:j, uf:sp and uf:bl double mutants were produced, and instead of inflorescences, they all developed solitary flowers just like the parental uf plants. These results suggest that UF may be a key gene that acts upstream of BL, S, J and SP in specifying the structure of the inflorescence. All the investigated mutants (simple and double) exhibited a delayed flowering on the various sympodial segments suggesting in most cases an interaction between the additional affected genes and SELF PRUNING (SP). Indeed, SP controls the sympodial growth of tomato and belongs to the CETS genes family. In addition to SP, this family contains 5 other members in tomato (the functions of which are yet unknown). We analysed the expression of the tomato CETS genes in different organs of the sp, uf, bl, s, j mutants and the generated double mutants. Our results indicate that qualitatively, mutation of UF, S, J and BL did not significantly affect the expression of members of the CETS family. The apparent absence of striking interactions at the transcriptional level may not preclude possible protein-protein interactions between SP and any of the UF, S, J or BL product. At the flower level, we extended observations reported in the literature and indicating that different floral traits are linked to the Lycopersicon incompatibility S-locus. We showed that the floral organs size and the number of flowers per inflorescence are genetically linked to the S-locus suggesting that a complex of tightly linked genes affecting separate aspects of reproductive biology may be located on tomato chromosome 1.