Measuring day length confers a strong fitness improvement to photosynthetic organisms as it allows them to anticipate light phases and take the best decisions preceding diurnal transitions. In close association with signals from the circadian clock and the photoreceptors, photoperiodic sensing constitutes also a precise way to determine the passing of the seasons and to take annual decisions such as the best time to flower or the beginning of dormancy. Photoperiodic sensing in photosynthetic organisms is ancient and two major stages in its evolution could be identified, the cyanobacterial time sensing and the evolutionary tool kit that arose in green algae and developed into the photoperiodic system of modern plants. The most recent discoveries about the evolution of the perception of light, measurement of day length and relationship with the circadian clock along the evolution of the eukaryotic green lineage will be discussed in this review.

Background:The cellular consequences of inorganic pyrophosphate excess in a eukaryotic cell are unknown. Results: Saccharomyces cerevisiae cells depleted of inorganic pyrophosphatase Ipp1p on respiratory carbon sources undergo cell cycle arrest, but fermenting cells undergo NAD ϩ depletion-induced autophagy and die.

Cancer cells show a metabolic shift that makes them overproduce protons; this has the potential to disturb the cellular acid-base homeostasis. However, these cells show cytoplasmic alkalinisation, increased acid extrusion and endosome-dependent drug resistance. Vacuolar type ATPases (V-ATPases), together with other transporters, are responsible to a great extent for these symptoms. These multi-subunit proton pumps are involved in the control of cytosolic pH and the generation of proton gradients (positive inside) across endocellular membrane systems like Golgi, endosomes or lysosomes. In addition, in tumours, they have been shown to play an important role in the acidification of the intercellular medium. This importance makes them an attractive target to control tumour cell proliferation. In the present review we present the major characteristics of this kind of proton pumps and we provide some recent insights on their in vivo regulation. Also, we review some of the consequences that V-ATPase inhibition carries for the tumour cell, such as cell cycle arrest or cell death, and provide a brief summary of the studies related to cancer made recently with commercially available inhibitors. In the light of recent knowledge on the regulation of this proton pump, some new approaches to impair V-ATPase function are also suggested.

Summary Flowering time is a key process in plant development. Photoperiodic signals play a crucial role in the floral transition in Arabidopsis thaliana, and the protein CONSTANS (CO) has a central regulatory function that is tightly regulated at the transcriptional and post‐translational levels. The stability of CO protein depends on a light‐driven proteasome process that optimizes its accumulation in the evening to promote the production of the florigen FLOWERING LOCUS T (FT) and induce seasonal flowering. To further investigate the post‐translational regulation of CO protein we have dissected its interactome network employing in vivo and in vitro assays and molecular genetics approaches. The immunophilin FKBP12 has been identified in Arabidopsis as a CO interactor that regulates its accumulation and activity. FKBP12 and CO interact through the CCT domain, affecting the stability and function of CO. fkbp12 insertion mutants show a delay in flowering time, while FKBP12 overexpression accelerates flowering, and these phenotypes can be directly related to a change in accumulation of FT protein. The interaction is conserved between the Chlamydomonas algal orthologs CrCO–CrFKBP12, revealing an ancient regulatory step in photoperiod regulation of plant development.

No abstract

8-Dehydrosterols are present in a wide range of biologically relevant situations, from human rare diseases to amine fungicide-treated fungi and crops. However, the molecular bases of their toxicity are still obscure. We show here that 8-dehydrosterols, but not other sterols, affect yeast vacuole acidification through V-ATPases. Moreover, erg2Δ cells display reductions in proton pumping rates consistent with ion-transport uncoupling in vitro. Concomitantly, subunit Vph1p shows conformational changes in the presence of 8-dehydrosterols. Expression of a plant vacuolar H(+)-pumping pyrophosphatase as an alternative H(+)-pump relieves Vma(-)-like phenotypes in erg2Δ-derived mutant cells. As a consequence of these acidification defects, endo- and exo-cytic traffic deficiencies that can be alleviated with a H(+)-pumping pyrophosphatase are also observed. Despite their effect on membrane traffic, 8-dehydrosterols do not induce endoplasmic reticulum stress or assembly defects on the V-ATPase. Autophagy is a V-ATPase dependent process and erg2Δ mutants accumulate autophagic bodies under nitrogen starvation similar to Vma(-) mutants. In contrast to classical Atg(-) mutants, this defect is not accompanied by impairment of traffic through the CVT pathway, processing of Pho8Δ60p, GFP-Atg8p localisation or difficulties to survive under nitrogen starvation conditions, but it is concomitant to reduced vacuolar protease activity. All in all, erg2Δ cells are autophagy mutants albeit some of their phenotypic features differ from classical Atg(-) defective cells. These results may pave the way to understand the aetiology of sterol-related diseases, the cytotoxic effect of amine fungicides, and may explain the tolerance to these compounds observed in plants.

The length of the day (photoperiod) is a robust seasonal signal originated by earth orbital and translational movements, a resilient external cue to the global climate change, and a predictable hint to initiate or complete different developmental programs. In eukaryotic algae, the gene expression network that controls the cellular response to photoperiod also regulates other basic physiological functions such as starch synthesis or redox homeostasis. Land plants, evolving in a novel and demanding environment, imbued these external signals within the regulatory networks controlling organogenesis and developmental programs. Unlike algae that largely have to deal with cellular physical cues, within the course of evolution land plants had to transfer this external information from the receiving organs to the target tissues, and mobile signals such as hormones were recruited and incorporated in the regulomes. Control of senescence by photoperiod, as suggested in this perspective, would be an accurate way to feed seasonal information into a newly developed function (senescence) using an ancient route (photoperiodic signaling). This way, the plant would assure that two coordinated aspects of development such as flowering and organ senescence were sequentially controlled. As in the case of senescence, there is growing evidence to support the idea that harnessing the reliability of photoperiod regulation over other, more labile signaling pathways could be used as a robust breeding tool to enhance plants against the harmful effects of climate change.

Plants are sessile organisms that have acquired highly plastic developmental strategies to adapt to the environment. Among these processes, the floral transition is essential to ensure reproductive success and is finely regulated by several internal and external genetic networks. The photoperiodic pathway, which controls the plant response to day length, is one of the most important pathways controlling flowering. In Arabidopsis photoperiodic flowering, CONSTANS (CO) is the central gene activating the expression of the florigen FLOWERING LOCUS T (FT) in the leaves at the end of a long day. CO expression is strongly regulated by the circadian clock. However, to date, no evidence has been reported regarding a feedback loop from the photoperiod pathway back to the circadian clock. Using transcriptional networks, we have identified relevant network motifs regulating the interplay between the circadian clock and the photoperiod pathway. Gene expression, chromatin immunoprecipitation experiments and phenotypic analysis allowed us to elucidate the role of CO over the circadian clock. Plants with altered CO expression showed a different internal clock period, measured by daily rhythmic movements in the leaves. We show that CO is able to activate key genes related to the circadian clock, such as CCA1, LHY, PRR5 and GI, at the end of a long day by binding to specific sites on their promoters. Moreover, a significant number of PRR5 repressed target genes are upregulated by CO, and this could explain the phase transition promoted by CO. The CO-PRR5 complex interacts with the bZIP transcription factor HY5 and helps to localize the complex in the promoters of clock genes. Our results indicate that there may be a feedback loop in which CO communicates back to the circadian clock, feeding seasonal information to the circadian system.