The tomato FT ortholog triggers systemic signals that regulate growth and flowering and substitute for diverse environmental stimuli

Abstract

Several indications implied that the Arabidopsis FT ( FLOW-ERING LOCUS T) gene provides a possible functional link between the systemic pathways and the cell-autonomous pathways to flowering. FT is a major integrator of the genetic pathways to flowering in short and long days (4, 5); it encodes a signaling factor (6, 7) and is not expressed in the SAM proper (8) but can be detected, upon induction, in shoot apices (SAPs) containing young leaves (9). Flowering is delayed in mutant ft plants (10, 11), and when FT is overexpressed, flowering occurs earlier with a determinate inflorescence (12, 13). FT is regulated by the flowering-time gene CONSTANS in both long-and short-day plants (14,15), and grafting experiments in Arabidopsis have shown that systemic induction of flowering by CONSTANS is most likely mediated by FT (16,17). It was recently shown that a small fraction of heat-shock-induced FT RNA, originating in a single leaf, is found in the SAPs, suggesting that the FT mRNA itself may represent a major component of florigen (18).We chose tomato, a photoperiod-insensitive plant, to test the premise that orthologs of the Arabidopsis FT gene can initiate a conserved, long-distance, flower-promoting pathway in diverse flowering systems. The generality of the florigen hypothesis was supported by interspecies grafting experiments (2). Grafting results are independent of the validity of promoters, the resolution of in situ hybridization patterns, inferences derived from the activation of upstream genes, or interpretations of clonal analysis. The perennial habit; the compound shoots, which permit the analysis of multiple vegetative͞floral transition events in one plant (19); and the ease of grafting render tomato as a useful experimental platform for investigating the nature of florigen. We expanded the analysis in tomato with parallel experiments in long-day Arabidopsis and short-day tobacco.The primary shoot of tomato is terminated by an inflorescence, after which the apparent main axis consists of an upright array of reiterated axillary branches called sympodial units (SUs). Each SU arises from the most proximal axillary bud of the preceding unit and consists of three vegetative nodes and a terminal inflorescence (Fig. 1A). The distinction between the primary and compound sections of sympodial plants provides two basic criteria for flowering time: the number of leaves to the first inflorescence in the primary shoot and the number of leaves between inflorescences in the compound part. Here, we identify the tomato FT ortholog as SINGLE FLOWER TRUSS (SFT), a gene regulating primary shoot flowering time, sympodial habit, and flower morphology. All aspects of the sft phenotype were complemented by graft-transmissible SFT signals, suggesting that all are the consequence of a common flowering-time defect. Significantly, graft-transmissible SFT signals substituted for light dose and two inductive photoperiodic stimuli in different species as well. ResultsThe Tomato Ortholog of FT Is Disrupted in Late-Flowering sft Mutants....

Flowering-time genes modulate meristem determinacy and growth form in Arabidopsis thaliana

“…These results suggest that FT-besides triggering flowering-also regulates the fate of meristems and consequently affects growth, especially under short days. That FT also regulates growth processes other than flowering has also been shown in tomato 23 .…”

A reverse genetics approach identifies novel mutants in light responses and anthocyanin metabolism in petunia

“…Photoperiodicflowering induction in model plants occurs via internal and external coincidence model (Song et al 2010), where the coincidence between the levels of CO mRNA and the illuminated or dark period of the day activates the transcription of FLOWERING LOCUS T (FT ) or its orthologs, which, in turn, are involved in the control of meristem-identity genes, shifting from vegetative to reproductive development (Turck et al 2008;Song et al 2010). In day-neutral tomato, the FT ortholog, SINGLE FLOWER TRUSS (SFT ), has been demonstrated to trigger the systemic signal responsible for pleiotropic regulation of growth and flowering (Lifschitz et al 2006). In potato, the ectopic expression of a rice FT gene elucidated the role of CO in controlling the photoperiodic processes flowering and tuberization (Navarro et al 2011).…”

Mejoramiento genético acelerado de angiospermas perennes vía inducción floral por sobre-expresión del gen FT

“…El gen FT está muy conservado entre las angiospermas; participa en la transición a la floración en plantas neutrales a la extensión del día como tomate (Lifschitz et al, 2006) y banana (Chaurasia et al, 2017), así como en plantas que requieren de vernalización (Yan et al, 2006), por lo que se le considera como un integrador de rutas de señalización.…”