Move on up, it’s time for change—mobile signals controlling photoperiod-dependent flowering

Abstract

Plants do not bloom randomly-but how do they know when and where to make flowers? Here, we review molecular mechanisms that integrate spatial and temporal information in day-length-dependent flowering. Primarily through genetic analyses in two species, Arabidopsis thaliana and rice, we today understand the essentials of two central issues in plant biology: how the appropriate photoperiod generates an inductive stimulus based on an external coincidence mechanism, and the nature of the mobile flowering signal, florigen, which relays photoperiod-dependent information from the leaf to the growing tip of the plant, the shoot apex.We all love springtime, not least because flowers are everywhere. But how do plants know it is the right time to bloom? Just like us, plants can recognize the seasons. Among different indicators such as temperature and light, the increase in day length is the most robust telltale sign that spring is upon us, at least for those of us who do not live in the tropics. The ability to recognize and respond to changes in day length is known as photoperiodism and is common to both plants and animals. In this review, we will focus on events downstream from the circadian clock that relay the photoperiodic signal from the site of perception, the leaves, to the shoot apex, where flowers are formed. Recent advances in this area have finally provided a molecular underpinning for two long-standing tenets of plant biology, the external coincidence model and the florigen hypothesis. The discovery of photoperiodic control of floweringOne of the first to recognize the importance of day length in flowering was the English botanist Arthur Henfrey (1852), who suggested that summer day length, which changes with latitude, is an important factor in determining where plants could grow. Some 50 years later, the French scientist Tournois (1912) found that both Humulus (hop) and Cannabis (hemp) flower precociously when kept in winter in a greenhouse supplemented with artificial light, in agreement with Henfrey's postulate. The German Klebs made similar observations with Sempervivum (house leek). Importantly, he realized that it was unlikely to be light quantity (as a nutritive factor, as he called it) but rather light duration (acting as a catalytic factor) that was critical in this process (summarized in Klebs 1913).Despite Tournois' and Klebs' contributions, the discovery of day length as a crucial factor in flowering control is generally accredited to Wightman Garner and Harry Allard, scientists at the US Department of Agriculture. Allard (1920, 1923) were working on two practical problems. One was the question of why certain strains of soybeans often would initiate flowers more or less simultaneously, typically during the height of summer, even if farmers had spread out the sowing dates. The other related to a tobacco variety that had spontaneously arisen in the field. This strain, appropriately called "Maryland Mammoth," would grow very tall, yielding nearly 100 leaves, whereas normal tobacco plants switch to ma...

Phototropins But Not Cryptochromes Mediate the Blue Light-Specific Promotion of Stomatal Conductance, While Both Enhance Photosynthesis and Transpiration under Full Sunlight

“…In Arabidopsis plants exposed to long days, cry (mainly cry2) promotes the expression of FT in vascular tissues (Endo et al, 2007;Kobayashi and Weigel, 2007), and the FT protein then migrates to the apex to induce the transition to flowering (Corbesier et al, 2007). Therefore, a role of FT in the cry-mediated effects on stomatal opening cannot be ruled out.…”

DTH8 Suppresses Flowering in Rice, Influencing Plant Height and Yield Potential Simultaneously

“…Photoperiod determines flowering time as the most important environment signal in plants. Arabidopsis (Arabidopsis thaliana), the model for long-day (LD) species, has been used to reveal how plants control flowering time induced by photoperiod (Corbesier et al, 2007;Kobayashi and Weigel, 2008). A series of genes about phytochrome, clock, and flowering have been found and a signal network has been built up.…”

Higher plants use LOV to perceive blue light

“…FKF1 promotes the expression of CO a central element of day-length-regulated flowering [34,36,38]. The regulation of CO occurs both at the transcriptional and post-translational level involving multiple photoreceptors from distinct families [34,36,42,43].…”

“…This review will not cover our knowledge of circadian biology and of the regulation of flowering by the photoperiod (for recent reviews please consult [34][35][36]), but briefly describe the mode of action of this novel class of blue light photoreceptors.…”

“…The regulation of CO occurs both at the transcriptional and post-translational level involving multiple photoreceptors from distinct families [34,36,42,43]. CO transcription is regulated by day length while the protein is unstable in the dark and stabilized during the day [34,36]. FKF1 regulates the stability of Cycling Dof Factor 1 (CDF1), which directly represses CO expression [44].…”