Eukaryote-specific assembly factor DEAP2 mediates an early step of photosystem II assembly in Arabidopsis

The initial step of oxygenic photosynthesis is the thermodynamically challenging extraction of electrons from water and the release of molecular oxygen. This light-driven process, which is the basis for most life on Earth, is catalyzed by photosystem II (PSII) within the thylakoid membrane of photosynthetic organisms. The biogenesis of PSII requires a controlled step-wise assembly process of which the early steps are considered to be highly conserved between plants and their cyanobacterial progenitors. This assembly process involves auxiliary proteins, which are likewise conserved. In the present work, we used Arabidopsis (Arabidopsis thaliana) as a model to show that in plants, a eukaryote-exclusive assembly factor facilitates the early assembly step, during which the intrinsic antenna protein CP47 becomes associated with the PSII reaction center (RC) to form the RC47 intermediate. This factor, which we named DECREASED ELECTRON TRANSPORT AT PSII (DEAP2), works in concert with the conserved PHOTOSYNTHESIS AFFECTED MUTANT 68 (PAM68) assembly factor. The deap2 and pam68 mutants showed similar defects in PSII accumulation and assembly of the RC47 intermediate. The combined lack of both proteins resulted in a loss of functional PSII and the inability of plants to grow photoautotrophically on the soil. While overexpression of DEAP2 partially rescued the pam68 PSII accumulation phenotype, this effect was not reciprocal. DEAP2 accumulated at 20-fold higher levels than PAM68, together suggesting that both proteins have distinct functions. In summary, our results uncover eukaryotic adjustments to the PSII assembly process, which involve the addition of DEAP2 for the rapid progression from RC to RC47.publishedVersio

LCAA, a Novel Factor Required for Magnesium Protoporphyrin Monomethylester Cyclase Accumulation and Feedback Control of Aminolevulinic Acid Biosynthesis in Tobacco

Low Chlorophyll Accumulation A (LCAA) antisense plants were obtained from a screen for genes whose partial down-regulation results in a strong chlorophyll deficiency in tobacco (Nicotiana tabacum). The LCAA mutants are affected in a plastid-localized protein of unknown function, which is conserved in cyanobacteria and all photosynthetic eukaryotes. They suffer from drastically reduced light-harvesting complex (LHC) contents, while the accumulation of all other photosynthetic complexes per leaf area is less affected. As the disturbed accumulation of LHC proteins could be either attributable to a defect in LHC biogenesis itself or to a bottleneck in chlorophyll biosynthesis, chlorophyll synthesis rates and chlorophyll synthesis intermediates were measured. LCAA antisense plants accumulate magnesium (Mg) protoporphyrin monomethylester and contain reduced protochlorophyllide levels and a reduced content of CHL27, a subunit of the Mg protoporphyrin monomethylester cyclase. Bimolecular fluorescence complementation assays confirm a direct interaction between LCAA and CHL27. 5-Aminolevulinic acid synthesis rates are increased and correlate with an increased content of glutamyl-transfer RNA reductase. We suggest that LCAA encodes an additional subunit of the Mg protoporphyrin monomethylester cyclase, is required for the stability of CHL27, and contributes to feedback-control of 5-aminolevulinic acid biosynthesis, the rate-limiting step of chlorophyll biosynthesis

Nationwide multicenter study on the management of pulmonary neuroendocrine (carcinoid) tumors.

Background/ Aim: To analyze the management and outcome of patients with primary typical (TC) and atypical lung carcinoids (AC) in Switzerland. METHODS Retrospective analysis of patients selected from a neuroendocrine tumor (NET) registry. Patients were divided into TC and AC according to pathology reports, and surgical procedures were grouped as wedge/ segmentectomy, lobectomy/ bi-lobectomy and pneumectomy. Survival analysis was performed using the Kaplan-Meier method and log-rank test. RESULTS Over 7 years, 113 pulmonary carcinoids (61.9% females, mean age 59.4 years) were included from 19 hospitals, with pathology data on Ki67 and necrosis incomplete in 16 cases. Eighty-three TC and 14 AC underwent surgical resection with a primary tumor size of median 14.5 range 1-80 mm and diagnosis was established in 55.8% at surgery. Mean follow-up was 30.2 23.1 months. Lobectomy was performed in 54.2% and wedge resection in 17.7% of cases. Six patients received additional systemic therapy. There was a trend for larger primary lesion size and a significantly higher rate of N2-N3 status in AC. Mean survival tended to be increased in patients with TC compared to AC (86.1 versus 48.4 months, p=0.06) and mean disease-free-interval after surgical resection was 74.1 and 48.3 months for TC and AC, respectively (p=0.74). CONCLUSION AC of the lung have a more malignant behavior and a trend to a worse outcome. The results of this registry reinforce the need for standardized histological diagnosis and inter-disciplinary therapeutic decision-making to improve the quality of care of patients with TC and AC

Nationwide multicenter study on the management of pulmonary neuroendocrine (carcinoid) tumors

Background and aim: To analyze the management and outcome of patients with primary typical (TC) and atypical lung carcinoids (AC) in Switzerland. Methods: Retrospective analysis of patients selected from a neuroendocrine tumor (NET) registry. Patients were divided into TC and AC according to pathology reports, and surgical procedures were grouped as wedge/segmentectomy, lobectomy/bilobectomy and pneumectomy. Survival analysis was performed using the Kaplan–Meier method and log-rank test. Results: Over 7 years, 113 pulmonary carcinoids (61.9% females, mean age 59.4 years) were included from 19 hospitals, with pathology data on Ki67 and necrosis incomplete in 16 cases. Eighty-three TC and 14 AC underwent surgical resection with a primary tumor size of median 14.5 (range 1–80) mm and diagnosis was established in 55.8% at surgery. Mean follow-up was 30.2 ± 23.1 months. Lobectomy was performed in 54.2% and wedge resection in 17.7% of cases. Six patients received additional systemic therapy. There was a trend for larger primary lesion size and a significantly higher rate of N2–N3 status in AC. Mean survival tended to be increased in patients with TC compared to AC (86.1 vs 48.4 months, P = 0.06) and mean disease-free interval after surgical resection was 74.1 and 48.3 months for TC and AC, respectively (P = 0.74). Conclusion: AC of the lung has a more malignant behavior and a trend to a worse outcome. The results of this registry reinforce the need for standardized histological diagnosis and inter-disciplinary therapeutic decision making to improve the quality of care of patients with TC and AC

The thylakoid membrane protein CGL160 supports CF1CF0 ATP synthase accumulation in Arabidopsis thaliana.

The biogenesis of the major thylakoid protein complexes of the photosynthetic apparatus requires auxiliary proteins supporting individual assembly steps. Here, we identify a plant lineage specific gene, CGL160, whose homolog, atp1, co-occurs with ATP synthase subunits in an operon-like arrangement in many cyanobacteria. Arabidopsis thaliana T-DNA insertion mutants, which no longer accumulate the nucleus-encoded CGL160 protein, accumulate less than 25% of wild-type levels of the chloroplast ATP synthase. Severe cosmetic or growth phenotypes result under either short day or fluctuating light growth conditions, respectively, but this is ameliorated under long day constant light growth conditions where the growth, ATP synthase activity and photosynthetic electron transport of the mutants are less affected. Accumulation of other photosynthetic complexes is largely unaffected in cgl160 mutants, suggesting that CGL160 is a specific assembly or stability factor for the CF1CF0 complex. CGL160 is not found in the mature assembled complex but it does interact specifically with subunits of ATP synthase, predominantly those in the extrinsic CF1 sub-complex. We suggest therefore that it may facilitate the assembly of CF1 into the holocomplex

Expression of a carotenogenic gene allows faster biomass production by redesigning plant architecture and improving photosynthetic efficiency in tobacco

Summary Because carotenoids act as accessory pigments in photosynthesis, play a key photoprotective role, and are of major nutritional importance, carotenogenesis has been a target for crop improvement. Although carotenoids are important precursors of phytohormones, previous genetic manipulations reported little if any effects on biomass production and plant development, but resulted in specific modifications in carotenoid content. Unexpectedly, the expression of the carrot lycopene b-cyclase (DcLCYB1) in Nicotiana tabacum cv. Xanthi not only resulted in increased carotenoid accumulation, but also in altered plant architecture characterized by longer internodes, faster plant growth, early flowering and increased biomass. Here, we have challenged these transformants with a range of growth conditions to determine the robustness of their phenotype and analyze the underlying mechanisms. Transgenic DcLCYB1 lines showed increased transcript levels of key genes involved in carotenoid, chlorophyll, gibberellin (GA) and abscisic acid (ABA) biosynthesis, but also in photosynthesis-related genes. Accordingly, their carotenoid, chlorophyll, ABA and GA contents were increased. Hormone application and inhibitor experiments confirmed the key role of altered GA/ABA contents in the growth phenotype. Because the longer internodes reduce shading of mature leaves, induction of leaf senescence was delayed, and mature leaves maintained a high photosynthetic capacity. This increased total plant assimilation, as reflected in higher plant yields under both fully-controlled constant and fluctuating light, and in non-controlled conditions. Furthermore, our data is a warning that engineering of isoprenoid metabolism can cause complex changes in phytohormone homeostasis and therefore plant development, which have not been sufficiently considered in previous studies