The nature of floral signals in Arabidopsis. II. Roles for FLOWERING LOCUS T (FT) and gibberellin

Abstract

Signals produced in leaves are transported to the shoot apex where they cause flowering. Protein of the gene FLOWERING LOCUS T (FT) is probably a long day (LD) signal in Arabidopsis. In the companion paper, rapid LD increases in FT expression associated with flowering driven photosynthetically in red light were documented. In a far red (FR)-rich LD, along with FT there was a potential role for gibberellin (GA). Here, with the GA biosynthesis dwarf mutant ga1-3, GA4-treated plants flowered after 26 d in short days (SD) but untreated plants were still vegetative after 6 months. Not only was FT expression low in SD but applied GA bypassed some of the block to flowering in ft-1. On transfer to LD, ga1-3 only flowered when treated simultaneously with GA, and FT expression increased rapidly (<19.5 h) and dramatically (15-fold). In contrast, in the wild type in LD there was little requirement for GA for FT increase and flowering so its endogenous GA content was near to saturating. Despite this permissive role for endogenous GA in Columbia, RNA interference (RNAi) silencing of the GA biosynthesis gene, GA 20-OXIDASE2, revealed an additional, direct role for GA in LD. Flowering took twice as long after silencing the LD-regulated gene, GA 20-OXIDASE2. Such independent LD input by FT and GA reflects their non-sympatric expression (FT in the leaf blade and GA 20-OXIDASE2 in the petiole). Overall, FT acts as the main LD floral signal in Columbia and GA acts on flowering both via and independently of FT.

TEMPRANILLO genes link photoperiod and gibberellin pathways to control flowering in Arabidopsis

“…As previously suggested, the GA pathway is also active in LD 27 but its action is masked by the photoperiod pathway; however, it becomes evident in co and ft mutants or in SD. It has already been shown that the GA pathway seems to be controlled by photoperiod 28,29 , and we propose that the GA signalling pathway might be controlled by day length via direct binding of TEM to two related genes involved in the production of bioactive GA 4 .…”

Cross-Repressive Interactions between SOC1 and the GATAs GNC and GNL/CGA1 in the Control of Greening, Cold Tolerance, and Flowering Time in Arabidopsis

“…GAs have been implicated in a variety of growth responses in plants, including the control of flowering time (Hisamatsu and King, 2008;Itoh et al, 2008;Schwechheimer, 2011). GAs are perceived by the GIBBERELLIC ACID-INSENSITIVE DWARF1 GA receptors, which in turn bind to and induce the degradation of DELLA repressors such as GIBBERELLIC ACID INSENSITIVE (GAI) and REPRESSOR OF ga1-3 (RGA) from Arabidopsis (Ueguchi-Tanaka et al, 2005;Griffiths et al, 2006;Willige et al, 2007).…”

“…In contrast, ga1-3 mutants failed to flower even after 5 to 6 months in short-day conditions, and this has given rise to the long-standing hypothesis that, in Arabidopsis, GA is essential for flowering only under short days (Wilson et al, 1992;Reeves and Coupland, 2001). Several recent studies, however, report a strong flowering time delay also under long days in ga1 mutants and other Arabidopsis GA pathway mutants when examined in the Columbia ecotype (Willige et al, 2007;Hisamatsu and King, 2008;Galvão et al, 2012;Porri et al, 2012).…”

Effects of Light Quality on Vegetative Growth and Flower Initiation in Phalaenopsis

“…In Arabidopsis, the relationship between gibberellin and Flowering Locus T (FT) has been evaluated. It was suggested that FT protein acts as a fl oral signal and that gibberellin promote fl owering through an independent pathway or by increasing the relative expression level of FT mRNA (Hisamatsu and King, 2008). In Miltoniopsis orchids, gibberellin application of 2.5 mM hasten the initiation of inflorescence during the first flowering season and it also increased the number of infl orescence per plant (Matsumoto and Brower, 2006).…”