Age-regulated microRNA156 (miR156) and targets similarly control the competence to flower in diverse species. By contrast, the diterpene hormone gibberellin (GA) and the microRNA319-regulated TEOSINTE BRANCHED/CYCLOIDEA/PCF (TCP) transcription factors promote flowering in the facultative long-day Arabidopsis thaliana, but suppress it in the day-neutral tomato (Solanum lycopersicum).We combined genetic and molecular studies and described a new interplay between GA and two unrelated miRNA-associated pathways that modulates tomato transition to flowering.Tomato PROCERA/DELLA activity is required to promote flowering along with the miR156-targeted SQUAMOSA PROMOTER BINDING-LIKE (SPL/SBP) transcription factors by activating SINGLE FLOWER TRUSS (SFT) in the leaves and the MADS-Box gene APETALA1(AP1)/MC at the shoot apex. Conversely, miR319-targeted LANCEOLATE represses floral transition by increasing GA concentrations and inactivating SFT in the leaves and AP1/MC at the shoot apex. Importantly, the combination of high GA concentrations/responses with the loss of SPL/SPB function impaired canonical meristem maturation and flower initiation in tomato.Our results reveal a cooperative regulation of tomato floral induction and flower development, integrating age cues (miR156 module) with GA responses and miR319-controlled pathways. Importantly, this study contributes to elucidate the mechanisms underlying the effects of GA in controlling flowering time in a day-neutral species.

The microRNA156 (miR156)/SQUAMOSA PROMOTER-BINDING PROTEIN-LIKE (SPL/SBP) regulatory hub is highly conserved among phylogenetically distinct species, but how it interconnects multiple pathways to converge to common integrators controlling shoot architecture is still unclear. Here, we demonstrated that the miR156/SlSBP15 hub modulates tomato shoot branching (SB) by connecting phytohormones with important genetic pathways regulating both axillary bud (AB) development and outgrowth. We verified that plants overexpressing the miR156 (156-OE plants) display high SB, whereas plants overexpressing a miR156-resistant SlSBP15 alelle (rSBP15 plants) display arrested SB and are able to partially restore the wild-type (WT) phenotype in156-OE background. Although rSBP15 plants showed ABs smaller than MT, its activation is dependent on shoot apex-derived auxin transport inhibition. Additionally, hormonal measurements reveal that IAA and ABA concentrations were lower in 156-OE and higher in rSBP15-OE plants. SlSBP15 regulates AB development and outgrowth by inhibiting auxin transport and the activity of GOBLET (GOB), and by interacting with BRANCHED1b (SlBRC1b) at the protein level to control abscisic acid (ABA) levels within ABs. Our data provide a new mechanism by which the miR156/SPL/SBP hub regulates SB, and suggest that SlSBP15 has potential applications in improving tomato architecture.

Many developmental processes associated with fruit development take place at the floral meristem (FM). Age-regulated microRNA156 (miR156) and gibberellins (GA) interact to control flowering time, but their interplay in subsequent stages of reproductive development is poorly understood. Here, we show that GA and miR156 function in tomato FM and fruit patterning. High GA responses or overexpression of miR156 (156OE), which leads to low levels of miR156-targeted SQUAMOSA PROMOTER BINDING PROTEIN LIKE (SPL/SBP), resulted in enlarged FMs, defects in FM determinacy and fruits with increased locule number. Conversely, low GA responses reduced fruit indeterminacy and locule number, and overexpression of a miR156 resistant SlSBP15 allele (rSBP15) reduced cell number and size in the FM, as well as locule number. GA responses were partially required for the fruit defects observed in 156OE and rSBP15 plants. Transcriptome analysis and genetic interactions revealed shared and divergent functions of miR156-targeted SlSBPs, PROCERA/DELLA and the classical WUSCHEL/CLAVATA pathway, which has been previously associated with meristem size and determinacy. Our findings reveal that the miR156/SlSBP/GA regulatory module is deployed differently depending on developmental stage and create novel opportunities to genetically fine tune aspects of fruit development that have been important for tomato domestication.

The microRNA156 (miR156)/SQUAMOSA PROMOTER-BINDING PROTEIN-LIKE (SPL/SBP) regulatory hub is highly conserved among phylogenetically distinct species, but how it interconnects multiple pathways to converge to common integrators controlling shoot architecture is still unclear. Here, we demonstrated that the miR156/SlSBP15 node modulates tomato shoot branching (SB) by connecting multiple phytohormones with classical genetic pathways regulating both axillary bud (AB) development and outgrowth. MiR156-overexpressing plants (156-OE) displayed high SB, whereas plants overexpressing a miR156-resistant SlSBP15 allele (rSBP15) showed arrested SB. Importantly, the rSBP15 allele was able to partially restore the wild-type SB phenotype in 156-OE background. rSBP15 plants have tiny ABs, and their activation is dependent on shoot apex-derived auxin transport inhibition. Hormonal measurements revealed that Indole-3-acetic acid (IAA) and abscisic acid (ABA) concentrations were lower in 156-OE and higher in rSBP15 ABs, respectively. Genetic and molecular data indicated that SlSBP15 regulates AB development and outgrowth by inhibiting auxin transport and GOBLET (GOB) activity, and by interacting with tomato BRANCHED1b (SlBRC1b) to control ABA levels within ABs. Collectively, our data provide a new mechanism by which the miR156/SPL/SBP hub regulates SB, and suggest that modulating SlSBP15 activity might have potential applications in shaping tomato shoot architecture.