Vernalization Pathway Research Articles

Multiple roles of Arabidopsis VRN1 in vernalization and flowering time control.

Arabidopsis VRN genes mediate vernalization, the process by which a long period of cold induces a mitotically stable state that leads to accelerated flowering during later development. VRN1 encodes a protein that binds DNA in vitro in a non-sequence-specific manner and functions in stable repression of the major target of the vernalization pathway, the floral repressor FLC. Overexpression of VRN1 reveals a vernalization-independent function for VRN1, mediated predominantly through the floral pathway integrator FT, and demonstrates that VRN1 requires vernalization-specific factors to target FLC.

Flowering on time: genes that regulate the floral transition. Workshop on the molecular basis of flowering time control.

The workshop was held at the John Innes Centre, Norwich, UK, July 11–14, 2001. http://www.jic.bbsrc.ac.uk/events/embo/. Workshop Administrator: Dee Rawsthorne, John Innes Centre, Norwich Research Park, Colney, Norwich NR4 7UH, Norfolk, UK (Tel: +44 1603 450527; Fax: +44 1603 450025; E‐mail: dee.rawsthorne@bbsrc.ac.uk). ![][1] Successful sexual reproduction in plants depends on the recognition of favourable environmental conditions and the integration of that information with endogenous developmental cues. Flowering in higher plants involves the transition of a vegetative meristem, producing leaves and stems, into a floral meristem, producing flowers. Most of our understanding of the regulation of the floral transition has been developed in the past 10 years using molecular genetic approaches in the model plant Arabidopsis thaliana , a rosette plant in which the initiation of flowering is followed by the elongation of the main stem. The two main environmental factors that promote flowering in Arabidopsis are long days (Figure 1) and exposure to low temperatures (vernalization). Genetic and physiological analysis of flowering time in Arabidopsis has led to the identification of a large number of flowering‐time genes (>80) that regulate flowering time in response to environmental and endogenous cues (reviewed by Simpson et al ., 1999). Regulation occurs through a complex network of genetic pathways, with two main pathways mediating environmental responses (the long‐day and vernalization pathways) and two pathways that function independently of environmental cues: the autonomous pathway, which promotes flowering under all conditions, and the gibberellin (GA) pathway, which is needed for flowering under non‐inductive short‐day conditions. These pathways converge in the induction of floral meristem identity genes and the floral transition (Figure 2). Many flowering‐time genes have been cloned recently, and the primary aim of the EMBO workshop in Norwich, and this report, was to highlight the most recent advances in our understanding of the molecular mechanisms regulating … [1]: /embed/graphic-1.gif

Memories of winter: vernalization and the competence to flower

ABSTRACTThe promotion of flowering in response to a prolonged exposure to cold temperatures (i.e. winter) is a useful adaptation for plant species that flower in the spring. This promotion is known as vernalization and results in a permanent memory of cold exposure. While the physiology of vernalization has been extensively studied in many species, the molecular mechanism of vernalization remains largely unknown. Recent studies, however, have revealed some of the molecular events that create the requirement for vernalization. In Arabidopsis, naturally occurring late‐flowering ecotypes and plants containing late‐flowering mutations in the autonomous floral‐promotion pathway are relatively late flowering unless cold treated. The vernalization requirement of these late‐flowering ecotypes and autonomous‐pathway mutants is largely created by an upregulation of the floral inhibitor FLOWERING LOCUS C (FLC). After cold treatment, as imbibed seeds or young seedlings, FLC transcript levels are downregulated and remain low for the remainder of the plant's life, but return to high levels in the next generation. Plants containing a constitutively expressed 35S:FLC construct remain late flowering after cold treatment, indicating that FLC levels must be downregulated for vernalization to be effective. Thus the epigenetic downregulation of FLC appears to be a major target of the vernalization pathway and provides a molecular marker of the vernalized state.

The AGAMOUS-LIKE 20 MADS domain protein integrates floral inductive pathways in Arabidopsis

The very late-flowering behavior of Arabidopsis winter-annual ecotypes is conferred mainly by two genes, FRIGIDA (FRI) and FLOWERING LOCUS C (FLC). A MADS-domain gene, AGAMOUS-LIKE 20 (AGL20), was identified as a dominant FRI suppressor in activation tagging mutagenesis. Overexpression of AGL20 suppresses not only the late flowering of plants that have functional FRI and FLC alleles but also the delayed phase transitions during the vegetative stages of plant development. Interestingly, AGL20 expression is positively regulated not only by the redundant vernalization and autonomous pathways of flowering but also by the photoperiod pathway. Our results indicate that AGL20 is an important integrator of three pathways controlling flowering in Arabidopsis.