Analysis of Flowering Time Control in Arabidopsis by Comparison of Double and Triple Mutants

Abstract

Three genetic pathways promote flowering of Arabidopsis under long photoperiods. These pathways are represented by the genes CO, FCA, and GA1, which act in the long-day, autonomous, and gibberellin pathways, respectively. To test whether these are the only pathways that promote flowering under long photoperiods, the co-2 fca-1 ga1-3 triple mutant was constructed. These plants never flowered under long-or short-day conditions, indicating that the three pathways impaired by these mutations are absolutely required for flowering under these conditions. The triple mutant background represents a "vegetative ground state" enabling the roles of single pathways to be described in the corresponding double mutants. The phenotypes of plants carrying all eight combinations of wild-type and mutant alleles at the three loci were compared under long-and short-day conditions. This analysis demonstrated that under long photoperiods the long-day pathway promoted flowering most effectively, whereas under short photoperiods the gibberellin pathway had the strongest effect. The autonomous pathway had a weak effect when acting alone under either photoperiod but appeared to play an important role in facilitating the promotion of flowering by the other two pathways. The vegetative phenotype of the triple mutant could be overcome by vernalization, suggesting that a fourth pathway promoted flowering under these conditions. These observations are discussed in light of current models describing the regulation of flowering time in Arabidopsis.

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

“…Based on the observation that the Landsberg erecta (Ler) allele of the GA biosynthesis mutant ga1-3 displays only a comparatively minor delay in flowering under long-day conditions, GA has for a long time been thought to be of minor importance for floral induction under long days. 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).…”

“…In long-day-grown wild-type plants, flowering is typically only moderately promoted by GA, because growth conditions in laboratory experiments are adjusted to guarantee a short generation time (Reeves and Coupland, 2001;Galvão et al, 2012). DELLA gene loss-of-function mutants with a constitutive GA response or spy mutants do not flower much faster than the wild type when grown under long days (Achard et al, 2003;Tseng et al, 2004).…”

Reciprocal control of flowering time by OsSOC1 in transgenic Arabidopsis and by FLC in transgenic rice

“…The activities of these, and a number of other genes, interact to bring about the vegetative to reproductive phase change. Arabidopsis triple mutants defective in the CO , FCA and GA1 genes fail to flower (Reeves and Coupland, 2001), but cold treatment can overcome the lack of flowering of the triple mutant, suggesting that the vernalization pathway can override blocks in the other pathways.…”

Nuclear factor Y-mediated H3K27me3 demethylation of the SOC1 locus orchestrates flowering responses of Arabidopsis

“…Molecular genetic analyses of GA and photoperiod pathways suggest that the photoperiod and GA pathways are coordinated to promote flowering under LDs 15,20,21 . The GA effect on flowering is genetically mediated by five DELLA proteins, GIBBERELLIC ACID INSENSITIVE (GAI), REPRESSOR OF ga1-3 (RGA), RGA-LIKE1 (RGL1), RGL2 and RGL3, which are key GA signalling repressors whose degradation is triggered by GA 22,23 .…”

“…The GA pathway also plays an important role in the promotion of flowering in Arabidopsis under both LDs and short days, although its effect under LDs is usually masked by the photoperiod pathway 19,20 . Molecular genetic analyses of GA and photoperiod pathways suggest that the photoperiod and GA pathways are coordinated to promote flowering under LDs 15,20,21 .…”