BackgroundCah3 is the only carbonic anhydrase (CA) isoform located in the thylakoid lumen of Chlamydomonas reinhardtii. Previous studies demonstrated its association with the donor side of the photosystem II (PSII) where it is required for the optimal function of the water oxidizing complex. However this enzyme has also been frequently proposed to perform a critical function in inorganic carbon acquisition and CO2 fixation and all mutants lacking Cah3 exhibit very poor growth after transfer to low CO2 conditions.Results/ConclusionsIn the present work we demonstrate that after transfer to low CO2, Cah3 is phosphorylated and that phosphorylation is correlated to changes in its localization and its increase in activity. When C. reinhardtii wild-type cells were acclimated to limiting CO2 conditions, the Cah3 activity increased about 5–6 fold. Under these conditions, there were no detectable changes in the level of the Cah3 polypeptide. The increase in activity was specifically inhibited in the presence of Staurosporine, a protein kinase inhibitor, suggesting that the Cah3 protein was post-translationally regulated via phosphorylation. Immunoprecipitation and in vitro dephosphorylation experiments confirm this hypothesis. In vivo phosphorylation analysis of thylakoid polypeptides indicates that there was a 3-fold increase in the phosphorylation signal of the Cah3 polypeptide within the first two hours after transfer to low CO2 conditions. The increase in the phosphorylation signal was correlated with changes in the intracellular localization of the Cah3 protein. Under high CO2 conditions, the Cah3 protein was only associated with the donor side of PSII in the stroma thylakoids. In contrast, in cells grown at limiting CO2 the protein was partly concentrated in the thylakoids crossing the pyrenoid, which did not contain PSII and were surrounded by Rubisco molecules.SignificanceThis is the first report of a CA being post-translationally regulated and describing phosphorylation events in the thylakoid lumen.

Cumulative evidence indicates that activation of cyclin D-dependent kinase 4/6 (cdk4/6) represents a major trigger of cell cycle reentry and apoptosis in vertebrate neurons. We show here the existence of another mechanism triggering cell cycle reentry in differentiating chick retinal neurons (DCRNs), based on phosphorylation of E2F4 by p38 MAPK . We demonstrate that the activation of p75 NTR by nerve growth factor (NGF) induces nuclear p38 MAPK kinase activity, which leads to Thr phosphorylation and subsequent recruitment of E2F4 to the E2F-responsive cdc2 promoter. Inhibition of p38MAPK , but not of cdk4/6, specifically prevents NGF-dependent cell cycle reentry and apoptosis in DCRNs. Moreover, a constitutively active form of chick E2F4 (Thr261Glu/Thr263Glu) stimulates G 1 /S transition and apoptosis, even after inhibition of p38 MAPK activity. In contrast, a dominant-negative E2F4 form (Thr261Ala/Thr263Ala) prevents NGF-induced cell cycle reactivation and cell death in DCRNs. These results indicate that NGF-induced cell cycle reentry in neurons depends on the activation of a novel, cdk4/6-independent pathway that may participate in neurodegeneration. Neurons have classically been considered as permanently postmitotic cells, but cumulative evidence has challenged this dogma. Several studies have demonstrated that under experimental or pathological conditions, neurons can reactivate the cell cycle, a phenomenon often linked with apoptosis (30). Nevertheless, the molecular mechanism triggering cell cycle reentry in neurons is far from been completely understood. Previous studies have pointed out to the upregulation of cyclin D and the activation of cyclin-dependent kinase 4/6 (cdk4/6) as a trigger for cell cycle reentry and apoptosis in neurons (24,45,60). In this regard, inhibition of cdk4/6 has been shown to protect neurons against apoptosis (61), likely by preventing E2F1 activity in these cells (40). Furthermore, activation of cdk4 in cortical neurons has been shown to induce hyperphosphorylation of the retinoblastoma protein (Rb) family member p130, followed by the release of E2F4 (45), derepression of B-and C-Myb (44), and induction of proapoptotic factor Bim (6). Nevertheless, cell cycle-dependent neuronal death could also be triggered by cyclin D-independent mechanisms. Thus, cell cycle-associated events linked with neurodegeneration in Alzheimer's disease (AD) can be dissociated from classical cell cycle initiation by cyclin D-cdk4/6. While 8% of AD hippocampal neurons have been shown to express nuclear cyclin B in vivo (9), only 0.6% of these neurons express detectable levels of cyclin D (9), mainly present in the cytoplasmic compartment (53). Therefore, cyclin D seems not to participate in cell cycle reactivation in AD.We have demonstrated that cell cycle reentry takes place in differentiating retinal ganglion cells (RGCs) during normal chick retina development (17, 51), a model system that may resemble AD-associated neurodegeneration (19). Cell cycle reentry in differentiating chick retinal neurons (D...

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Aim Mediterranean Chile is part of the five recognized mediterranean‐type climates in the world and harbours a very rich floral diversity. Climate change has been reported as a significant threat to its biodiversity. We used the flora of Mediterranean Chile to analyse how biodiversity patterns, as measured by phylogenetic diversity, genus and species richness will respond to climate change scenarios and identify the areas that will harbour the greatest evolutionary potential and biodiversity richness. We also evaluated how these spatial patterns are depicted within the current network of protected areas. Location Chilean Mediterranean climate‐type Region, South America. Methods Biodiversity metrics were evaluated for current and future climatic scenarios. Species distribution models were done using Maxent for 1.727 species and 571 genera. Relationships between species/genera gain, loss and turnover were evaluated. For Mediterranean endemic species, loss and gain were also related to life‐form. Finally, variation in species gain, loss and turnover was evaluated in future climate change scenarios within and outside Mediterranean Chile state protected areas. Results We found a general decrease in species richness in the entire Region towards future climate change scenarios. Phylogenetic diversity is predicted to be higher than expected by richness in the north–south of the area and lower than expected by richness in the Andes Mountain. The highest average species and genus loss is predicted to occur outside the protected areas; meanwhile, species and genus gain is higher within them. Main conclusions Future biodiversity patterns are reported here for the first time in the Chilean Mediterranean Region. Our findings enhance the importance of the current protected areas to harbour this future variation, despite their reduced number and size along the region.

The establishment of species boundaries has been a difficult task for biologists since the beginning of classifications. Within South American Allioideae (= Alliaceae), the delimitation of genera and species has long been a major challenge. Consequently, species‐level nomenclature in these groups has been difficult to elucidate. Ipheion and Tristagma are two closely related South American genera for which the delimitation and circumscription of several species continue to be unclear. Tristagma sessile, a species inhabiting the Andes and the Coast Range in Chile, and Ipheion recurvifolium, a species native to Uruguay only found close to sea level, have been considered as one species with an intracontinental disjunct distribution. The divergent habitats and distributions of these taxa have stirred the question of whether they are a single species. The present study aims to elucidate the evolutionary relationships and status of the Chilean and Pampean taxa. We also analysed the name Tristagma leichtlinii, which has long been a source of confusion. Based on their phylogenetic relationships, geographical distributions, flowering periods, and DNA content, we conclude that the two taxa are different species and assignable to separate genera. We propose that the morphological similarity of Ipheion recurvifolium and Tristagma sessile, amply corroborated in this study, might be the sum of shared synapomorphies (between Ipheion and Tristagma) and convergent features. We update the biogeographic history of the two genera and propose that similar pollinators might underpin the convergence in floral traits. We outline the differences among genera and species, present a taxonomic review with a new lectotype and consider the conservation status of the studied species.