TM3 and STM3 Promote Flowering Together with FUL2 and MBP20, but Act Antagonistically in Inflorescence Branching in Tomato

Abstract

The moment at which a plant transitions to reproductive development is paramount to its life cycle and is strictly controlled by many genes. The transcription factor SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1) plays a central role in this process in Arabidopsis. However, the role of SOC1 in tomato (Solanum lycopersicum) has been sparsely studied. Here, we investigated the function of four tomato SOC1 homologs in the floral transition and inflorescence development. We thoroughly characterized the SOC1-like clade throughout the Solanaceae and selected four tomato homologs that are dynamically expressed upon the floral transition. We show that of these homologs, TOMATO MADS 3 (TM3) and SISTER OF TM3 (STM3) promote the primary and sympodial transition to flowering, while MADS-BOX PROTEIN 23 (MBP23) and MBP18 hardly contribute to flowering initiation in the indeterminate cultivar Moneyberg. Protein–protein interaction assays and whole-transcriptome analysis during reproductive meristem development revealed that TM3 and STM3 interact and share many targets with FRUITFULL (FUL) homologs, including cytokinin regulators. Furthermore, we observed that mutating TM3/STM3 affects inflorescence development, but counteracts the inflorescence-branching phenotype of ful2 mbp20. Collectively, this indicates that TM3/STM3 promote the floral transition together with FUL2/MBP20, while these transcription factors have opposite functions in inflorescence development.

New Advances in the Study of Regulation of Tomato Flowering-Related Genes Using Biotechnological Approaches

“…At the same time, FUL1 most likely exhibits secondary functions during flowering, which the authors could not clarify. TM3/STM3 presumably controls floral transition by interacting with FUL2/MBP20 in a protein complex and repressing cytokinin inhibitors but subsequently exhibits antagonistic functions in determining FM and IM identity [69]. MBP10 is expressed at weak to moderate levels, and its atypical short first intron lacks putative transcription factor binding sites, indicating possible pseudogenization [67].…”

A SEPALLATA MADS-Box Transcription Factor, SlMBP21, Functions as a Negative Regulator of Flower Number and Fruit Yields in Tomato

“…Overexpression of two SHORT VEGETATIVE PHASE (SVP) MADS-box genes OsMADS22 and OsMADS55 in rice results in increased flower numbers via the repression of meristem phase transition [45]. In tomato, four MADS-box genes, TM3, STM3, FUL2, and SlMBP20, are reported to regulate tomato inflorescence development; the ful2mbp20 mutants display the increased inflorescence branches with a large number of flowers [46,47]. STM3 is also reported to regulate flower number by regulating the inflorescence meristem via activating FRUITFULL1, and overexpression of STM3 results in highly branched inflorescences with a large flower number [48].…”