Flowering is a hot topic in Plant Biology and important progress has been made in Arabidopsis thaliana toward unraveling the genetic networks involved. The increasing complexity and the explosion of literature however require development of new tools for information management and update. We therefore created an evolutive and interactive database of flowering time genes, named FLOR-ID (Flowering-Interactive Database), which is freely accessible at http://www.flor-id.org. The hand-curated database contains information on 306 genes and links to 1595 publications gathering the work of >4500 authors. Gene/protein functions and interactions within the flowering pathways were inferred from the analysis of related publications, included in the database and translated into interactive manually drawn snapshots.

SUMMARYCytokinins are involved in many aspects of plant growth and development, and physiological evidence also indicates that they have a role in floral transition. In order to integrate these phytohormones into the current knowledge of genetically defined molecular pathways to flowering, we performed exogenous treatments of adult wild type and mutant Arabidopsis plants, and analysed the expression of candidate genes. We used a hydroponic system that enables synchronous growth and flowering of Arabidopsis, and allows the precise application of chemicals to the roots for defined periods of time. We show that the application of N 6 -benzylaminopurine (BAP) promotes flowering of plants grown in non-inductive short days. The response to cytokinin treatment does not require FLOWERING LOCUS T (FT), but activates its paralogue TWIN SISTER OF FT (TSF), as well as FD, which encodes a partner protein of TSF, and the downstream gene SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1). Treatment of selected mutants confirmed that TSF and SOC1 are necessary for the flowering response to BAP, whereas the activation cascade might partially act independently of FD. These experiments provide a mechanistic basis for the role of cytokinins in flowering, and demonstrate that the redundant genes FT and TSF are differently regulated by distinct floral-inducing signals.

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Perception of seasonal cues is critical for reproductive success in many plants. Exposure to winter cold is a cue that can confer competence to flower in the spring via a process known as vernalization. In certain grasses, exposure to short days is another winter cue that can lead to a vernalized state. In Brachypodium distachyon, we find that natural variation for the ability of short days to confer competence to flower is due to allelic variation of the FLOWERING LOCUS T (FT1) paralog FT-like9 (FTL9). An active FTL9 allele is required for the acquisition of floral competence, demonstrating a novel role for a member of the FT family of genes. Loss of the short-day vernalization response appears to have arisen once in B. distachyon and spread through diverse lineages indicating that this loss has adaptive value, perhaps by delaying spring flowering until the danger of cold damage to flowers has subsided.

A requirement for vernalization, the process by which prolonged cold exposure provides competence to flower, is an important adaptation to temperate climates that ensures flowering does not occur before the onset of winter. In temperate grasses, vernalization results in the up-regulation of VERNALIZATION1 (VRN1) to establish competence to flower; however, little is known about the mechanism underlying repression of VRN1 in the fall season, which is necessary to establish a vernalization requirement. Here, we report that a plant-specific gene containing a bromo-adjacent homology and transcriptional elongation factor S-II domain, which we named REPRESSOR OF VERNALIZATION1 (RVR1), represses VRN1 before vernalization in Brachypodium distachyon. That RVR1 is upstream of VRN1 is supported by the observations that VRN1 is precociously elevated in an rvr1 mutant, resulting in rapid flowering without cold exposure, and the rapid-flowering rvr1 phenotype is dependent on VRN1. The precocious VRN1 expression in rvr1 is associated with reduced levels of the repressive chromatin modification H3K27me3 at VRN1, which is similar to the reduced VRN1 H3K27me3 in vernalized plants. Furthermore, the transcriptome of vernalized wild-type plants overlaps with that of nonvernalized rvr1 plants, indicating loss of rvr1 is similar to the vernalized state at a molecular level. However, loss of rvr1 results in more differentially expressed genes than does vernalization, indicating that RVR1 may be involved in processes other than vernalization despite a lack of any obvious pleiotropy in the rvr1 mutant. This study provides an example of a role for this class of plant-specific genes.A common adaptation for optimal timing of flowering in temperate climates is the evolution of a vernalization requirement. Vernalization is the process by which plants become competent to flower after prolonged exposure to the cold temperatures of winter (1). Cold exposure alone, however, is typically not sufficient to induce flowering; rather, it often must be followed by an inductive photoperiod, such as the increasing day lengths of spring. The combination of a requirement for a prolonged period of cold followed by a requirement for increasing day lengths has the adaptive value of preventing flowering in the fall season before the onset of winter, which would likely compromise reproductive success (2).To date, information about the vernalization response in grasses has largely been derived from studies of existing allelic variation in wheat and barley (for reviews, see refs. 3-5). Wheat and barley varieties can be classified as either spring or winter types. Spring varieties do not require vernalization to flower rapidly in inductive long days (LD), whereas vernalization enables rapid flowering of winter varieties (5, 6). A current molecular model of vernalization in temperate grasses consists of a regulatory loop including the genes VERNALIZATION1 (VRN1), VERNALIZATION2 (VRN2), and VERNALIZATION3