Integration of photoperiod and cold temperature signals into flowering genetic pathways in Arabidopsis

Appropriate timing of flowering is critical for propagation and reproductive success in plants. Therefore, flowering time is coordinately regulated by endogenous developmental programs and external signals, such as changes in photoperiod and temperature. Flowering is delayed by a transient shift to cold temperatures that frequently occurs during early spring in the temperate zones. It is known that the delayed flowering by short-term cold stress is mediated primarily by the floral repressor FLOWERING LOCUS C (FLC). However, how the FLC-mediated cold signals are integrated into flowering genetic pathways is not fully understood. We have recently reported that the INDUCER OF CBF EXPRESSION 1 (ICE1), which is a master regulator of cold responses, FLC, and the floral integrator SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1) constitute an elaborated feedforward-feedback loop that integrates photoperiod and cold temperature signals to regulate seasonal flowering in Arabidopsis. Cold temperatures promote the binding of ICE1 to FLC promoter to induce its expression, resulting in delayed flowering. However, under floral inductive conditions, SOC1 induces flowering by blocking the ICE1 activity. We propose that the ICE1-FLC-SOC1 signaling network fine-tunes the timing of photoperiodic flowering during changing seasons.     

FLC调控植物成花的分子机制研究新进展

FLC是植物成花关键抑制因子, 主要通过结合到其下游2个关键的成花促进基因(FT和SOC1)启动子上而抑制二者的表达。此外, 还可以与其它调控因子结合调控开花。然而, 关于FLC在成花调控中的具体分子机制仍需深入研究。该文主要结合8条成花调控遗传途径, 梳理近年来与FLC相关的新进展, 并展望了未来的研究方向。     

FLC or not FLC: the other side of vernalization

Vernalization is the promotion of the competence for floweringby long periods of low temperatures such as those typicallyexperienced during winters. In Arabidopsis, the vernalizationresponse is, to a large extent, mediated by the repression ofthe floral repressor FLC, and the stable epigenetic silencingof FLC after cold treatments is essential for vernalization.In addition to FLC, other vernalization targets exist in Arabidopsis.In grasses, vernalization seems to be entirely independent ofFLC. Here, the current understanding of FLC-independent branchesof the vernalization pathway in Arabidopsis and vernalizationwithout FLC in grasses is discussed. This review focuses onthe role of AGL19, AGL24, and the MAF genes in Arabidopsis.Interestingly, vernalization acts through related molecularmachineries on distinct targets. In particular, protein complexessimilar to Drosophila Polycomb Repressive Complex 2 play a prominentrole in establishing an epigenetic cellular memory for cold-regulatedexpression states of AGL19 and FLC. Finally, the similar networktopology of the apparently independently evolved vernalizationpathways of grasses and Arabidopsis is discussed. Key words: AGL19, Arabidopsis, chromatin, epigenetics, FLC, flowering time, polycomb, PRC2, vernalization Received 19 December 2007; Revised 11 February 2008 Accepted 15 February 2008     

Overexpression of a Kunitz-type trypsin inhibitor (AtKTI1) causes early flowering in Arabidopsis

An early flowering mutant of Arabidopsis, elf32-D was isolated from activation tagging screening. The mutant flowered earlier than wild type under both long day and short day conditions. The mutant phenotype was caused by overexpression of a Kunitz-type trypsin inhibitor gene (AtKTI1). The expression of AtKTI1 was detected in leaves, flowers, siliques and roots. In the vegetative state, no change of flowering integrator gene expression was observed for AtKTI1 overexpressing plants. In contrast, at the reproductive stage, its overexpression resulted in the down-regulation of FLC, a strong floral repressor which integrates the autonomous and vernalization pathways and also the up-regulation of FT and AP1, which are downstream floral integrator genes. It is probable that the AtKTI1 overexpression inhibits components of the flowering signaling pathway upstream of FLC, eventually regulating expression of FLC, or causing perturbations in plant metabolism and thus indirectly affecting flowering.     

拟南芥开花时间调控的分子基础

在合适的时间开花对大多数植物的生存和成功繁衍极为重要。开花时间受错综复杂的环境因素和植物自身的遗传因子影响,由开花调控因子所构成的光周期、春化、温度、赤霉素、自主以及年龄等至少6条既相互独立又相互联系的遗传途径调控。该文综述了有关拟南芥(Arabidopsis thaliana)开花时间调控的分子机制的最新研究进展,并对今后的研究进行了展望。     

高等植物开花时程的调控与光受体Ⅰ.开花时程的基因与光受体调控

系统评述了高等植物开花时程的调控与植物光受体的联系.重点说明了控制开花时程的遗传途径以及光周期途径的有关基因的研究进展.影响高等植物开花的最重要的因子之一便是光周期,光周期对高等植物开花的调控是通过相关基因间的相互作用来实现的,这些基因包括参与花启动发育控制基因,昼夜节律时间钟调控基因及光受体信号转导基因.近5年左右的时间通过对拟南芥及其一系列突变体的研究为我们展示了这一热门领域的广阔的前景.