Impacto de la pandemia por COVID-19 en la formación de los cirujanos torácicos en España / Impact of the COVID-19 pandemic on thoracic surgery training in Spain

Tras más de dos años desde su aparición, la pandemia por SARS-CoV-2 ha generado importantes cambios en la sanidad y su organización. El presente trabajo trata de dilucidar las implicaciones de estos en la formación especializada de la cirugía torácica y sus repercusiones en los profesionales. Para ello, desde la Sociedad Española de Cirugía Torácica (SECT) se distribuye una encuesta entre los residentes en activo y aquellos que han terminado su formación en los últimos tres años. Esta consta de 24 preguntas cerradas de respuesta múltiple sobre el impacto de la pandemia en sus servicios, su formación y su vivencia. La tasa de respuesta (TR) de la encuesta fue de 42% (52 de una población objetivo de 120). El efecto de la pandemia en el funcionamiento de los servicios de cirugía torácica fue considerado alto o extremo según 78,8% de los participantes. Las actividades académicas fueron completamente suspendidas en 42,3% de los casos, mientras que 57,7% de los participantes tuvieron que prestar atención asistencial a pacientes ingresados por COVID, de los cuales 25% fue a tiempo parcial y 32,7% a tiempo completo. De los encuestados, 80% consideró que los cambios sufridos durante la pandemia afectaron su formación como residente y 36,5% opinó que debería ofrecerse una prolongación del periodo de formación para quienes se hayan visto afectados. Así pues, observamos cómo la pandemia ha afectado profundamente de forma negativa la formación especializada en cirugía torácica en España. (AU)

In the more than 2 years since its emergence, the SARS-CoV-2 pandemic has prompted important changes in healthcare systems and their organization. The aim of this study is to determine the implications in specialized thoracic surgery training as well as the repercussions on thoracic surgery residents. With this objective, the Spanish Society of Thoracic Surgery has conducted a survey among all its trainees and those who had finished their residency during the last 3 years. It consisted of 24 multiple-answer closed questions about the impact of the pandemic on their services, their training, and their personal experience. The response rate was 42% (52 out of a target population of 120). The effect of the pandemic on thoracic surgery services was high or extreme according to 78.8% of the participants. Academic activities were completely cancelled in 42.3% of the cases, and 57.7% of the respondents were required to treat hospitalized COVID patients (25% part-time, and 32.7% full-time). More than 80% of the survey participants believed that changes during the pandemic negatively affected their training, and 36.5% would prefer to extend their training period. In sum, we observe how the pandemic has had deep negative effects on specialized training in thoracic surgery in Spain. (AU)

Impact of COVID-19 pandemic in thoracic surgery training in Spain.

In the more than 2 years since its emergence, the SARS-CoV-2 pandemic has prompted important changes in healthcare systems and their organization. The aim of this study is to determine the implications in specialized thoracic surgery training as well as the repercussions on thoracic surgery residents. With this objective, the Spanish Society of Thoracic Surgery has conducted a survey among all its trainees and those who had finished their residency during the last 3 years. It consisted of 24 multiple-answer closed questions about the impact of the pandemic on their services, their training, and their personal experience. The response rate was 42% (52 out of a target population of 120). The effect of the pandemic on thoracic surgery services was high or extreme according to 78.8% of the participants. Academic activities were completely cancelled in 42.3% of the cases, and 57.7% of the respondents were required to treat hospitalized COVID patients (25% part-time, and 32.7% full-time). More than 80% of the survey participants believed that changes during the pandemic negatively affected their training, and 36.5% would prefer to extend their training period. In sum, we observe how the pandemic has had deep negative effects on specialized training in thoracic surgery in Spain.

[Impact of the COVID-19 pandemic on thoracic surgery training in Spain]. / Impacto de la pandemia por COVID-19 en la formación de los cirujanos torácicos en España.

In the more than 2 years since its emergence, the SARS-CoV-2 pandemic has prompted important changes in healthcare systems and their organization. The aim of this study is to determine the implications in specialized thoracic surgery training as well as the repercussions on thoracic surgery residents. With this objective, the Spanish Society of Thoracic Surgery has conducted a survey among all its trainees and those who had finished their residency during the last 3 years. It consisted of 24 multiple-answer closed questions about the impact of the pandemic on their services, their training, and their personal experience. The response rate was 42% (52 out of a target population of 120). The effect of the pandemic on thoracic surgery services was high or extreme according to 78.8% of the participants. Academic activities were completely cancelled in 42.3% of the cases, and 57.7% of the respondents were required to treat hospitalized COVID patients (25% part-time, and 32.7% full-time). More than 80% of the survey participants believed that changes during the pandemic negatively affected their training, and 36.5% would prefer to extend their training period. In sum, we observe how the pandemic has had deep negative effects on specialized training in thoracic surgery in Spain.

Iron Deficiency Promotes the Lack of Photosynthetic Cytochrome c550 and Affects the Binding of the Luminal Extrinsic Subunits to Photosystem II in the Diatom Phaeodactylum tricornutum.

In the diatom Phaeodactylum tricornutum, iron limitation promotes a decrease in the content of photosystem II, as determined by measurements of oxygen-evolving activity, thermoluminescence, chlorophyll fluorescence analyses and protein quantification methods. Thermoluminescence experiments also indicate that iron limitation induces subtle changes in the energetics of the recombination reaction between reduced QB and the S2/S3 states of the water-splitting machinery. However, electron transfer from QA to QB, involving non-heme iron, seems not to be significantly inhibited. Moreover, iron deficiency promotes a severe decrease in the content of the extrinsic PsbV/cytochrome c550 subunit of photosystem II, which appears in eukaryotic algae from the red photosynthetic lineage (including diatoms) but is absent in green algae and plants. The decline in the content of cytochrome c550 under iron-limiting conditions is accompanied by a decrease in the binding of this protein to photosystem II, and also of the extrinsic PsbO subunit. We propose that the lack of cytochrome c550, induced by iron deficiency, specifically affects the binding of other extrinsic subunits of photosystem II, as previously described in cyanobacterial PsbV mutants.

Neuromorphic Signal Filter for Robot Sensoring.

Noise management associated with input signals in sensor devices arises as one of the main problems limiting robot control performance. This article introduces a novel neuromorphic filter model based on a leaky integrate and fire (LIF) neural model cell, which encodes the primary information from a noisy input signal and delivers an output signal with a significant noise reduction in practically real-time with energy-efficient consumption. A new approach for neural decoding based on the neuron-cell spiking frequency is introduced to recover the primary signal information. The simulations conducted on the neuromorphic filter demonstrate an outstanding performance of white noise rejecting while preserving the original noiseless signal with a low information loss. The proposed filter model is compatible with the CMOS technology design methodologies for implementing low consumption smart sensors with applications in various fields such as robotics and the automotive industry demanded by Industry 4.0.

The mitochondrial and chloroplast dual targeting of a multifunctional plant viral protein modulates chloroplast-to-nucleus communication, RNA silencing suppressor activity, encapsidation, pathogenesis and tissue tropism.

Plant defense against melon necrotic spot virus (MNSV) is triggered by the viral auxiliary replicase p29 that is targeted to mitochondrial membranes causing morphological alterations, oxidative burst and necrosis. Here we show that MNSV coat protein (CP) was also targeted to mitochondria and mitochondrial-derived replication complexes [viral replication factories or complex (VRC)], in close association with p29, in addition to chloroplasts. CP import resulted in the cleavage of the R/arm domain previously implicated in genome binding during encapsidation and RNA silencing suppression (RSS). We also show that CP organelle import inhibition enhanced RSS activity, CP accumulation and VRC biogenesis but resulted in inhibition of systemic spreading, indicating that MNSV whole-plant infection requires CP organelle import. We hypothesize that to alleviate the p29 impact on host physiology, MNSV could moderate its replication and p29 accumulation by regulating CP RSS activity through organelle targeting and, consequently, eluding early-triggered antiviral response. Cellular and molecular events also suggested that S/P domains, which correspond to processed CP in chloroplast stroma or mitochondrion matrix, could mitigate host response inhibiting p29-induced necrosis. S/P deletion mainly resulted in a precarious balance between defense and counter-defense responses, generating either cytopathic alterations and MNSV cell-to-cell movement restriction or some degree of local movement. In addition, local necrosis and defense responses were dampened when RSS activity but not S/P organelle targeting was affected. Based on a robust biochemical and cellular analysis, we established that the mitochondrial and chloroplast dual targeting of MNSV CP profoundly impacts the viral infection cycle.

Chaperone-mediated autophagy prevents collapse of the neuronal metastable proteome.

Components of the proteostasis network malfunction in aging, and reduced protein quality control in neurons has been proposed to promote neurodegeneration. Here, we investigate the role of chaperone-mediated autophagy (CMA), a selective autophagy shown to degrade neurodegeneration-related proteins, in neuronal proteostasis. Using mouse models with systemic and neuronal-specific CMA blockage, we demonstrate that loss of neuronal CMA leads to altered neuronal function, selective changes in the neuronal metastable proteome, and proteotoxicity, all reminiscent of brain aging. Imposing CMA loss on a mouse model of Alzheimer's disease (AD) has synergistic negative effects on the proteome at risk of aggregation, thus increasing neuronal disease vulnerability and accelerating disease progression. Conversely, chemical enhancement of CMA ameliorates pathology in two different AD experimental mouse models. We conclude that functional CMA is essential for neuronal proteostasis through the maintenance of a subset of the proteome with a higher risk of misfolding than the general proteome.

New Insights into the Evolution of the Electron Transfer from Cytochrome f to Photosystem I in the Green and Red Branches of Photosynthetic Eukaryotes.

In cyanobacteria and most green algae of the eukaryotic green lineage, the copper-protein plastocyanin (Pc) alternatively replaces the heme-protein cytochrome c6 (Cc6) as the soluble electron carrier from cytochrome f (Cf) to photosystem I (PSI). The functional and structural equivalence of 'green' Pc and Cc6 has been well established, representing an example of convergent evolution of two unrelated proteins. However, plants only produce Pc, despite having evolved from green algae. On the other hand, Cc6 is the only soluble donor available in most species of the red lineage of photosynthetic organisms, which includes, among others, red algae and diatoms. Interestingly, Pc genes have been identified in oceanic diatoms, probably acquired by horizontal gene transfer from green algae. However, the mechanisms that regulate the expression of a functional Pc in diatoms are still unclear. In the green eukaryotic lineage, the transfer of electrons from Cf to PSI has been characterized in depth. The conclusion is that in the green lineage, this process involves strong electrostatic interactions between partners, which ensure a high affinity and an efficient electron transfer (ET) at the cost of limiting the turnover of the process. In the red lineage, recent kinetic and structural modeling data suggest a different strategy, based on weaker electrostatic interactions between partners, with lower affinity and less efficient ET, but favoring instead the protein exchange and the turnover of the process. Finally, in diatoms the interaction of the acquired green-type Pc with both Cf and PSI may not yet be optimized.

Retrasplante pulmonar. Experiencia de un centro de referencia / Lung retransplant. Experience of a referral centre

ANTECEDENTES Y OBJETIVOS: El retrasplante pulmonar (RTP) es un tratamiento válido en pacientes con disfunción pulmonar, pero con una elevada morbimortalidad. Nuestro objetivo es analizar nuestra experiencia en RTP en supervivencia y función pulmonar. PACIENTES Y MÉTODOS: Estudio retrospectivo de pacientes con RTP (1990-2019). VARIABLES: receptores y procedimiento, mortalidad precoz, supervivencia y función pulmonar en pacientes CLAD. Variables cuantitativas (media±DE); cualitativas (%). Se utilizó el test t de Student o χ2. La supervivencia se estimó mediante Kaplan-Meier, comparándose con Log Rank. Se estableció como significativa p < 0,05. RESULTADOS: De 784 pacientes trasplantados, 25 pacientes (edad media 38,41 ± 16,3 años, 12 hombres y 13 mujeres) fueron RTP; CLAD (n = 19), infarto pulmonar (n = 2), complicaciones de vía aérea (n = 2), disfunción del injerto (n = 1), rechazo hiperagudo (n = 1). Tiempo medio hasta el retrasplante: 5,41 ± 3,87 años en CLAD y 21,2 ± 21,4 días en no CLAD. La mortalidad a 90 días fue del 52% y 36,8% en el segundo periodo (p = 0,007), siendo mayor en pacientes que precisaron ECMO preoperatorio (80 vs. 20%, p = 0,04). La supervivencia a 1 y 5 años fue del 53,9% y 37,7%, respectivamente (p = 0,016). La supervivencia del grupo CLAD fue mayor (p = 0,08). El ECMO pre RTP disminuyó la supervivencia (p = 0,032). FEV1 mejoró una media de 0,98 ± 0,13L (25,6 ± 18,8%) (p = 0,001). CONCLUSIONES: El RTP es un procedimiento de elevada mortalidad que obliga a una cuidadosa selección de los pacientes, con mejores resultados en aquellos con CLAD. La función pulmonar de los pacientes con CLAD mejoró significativamente

BACKGROUND: Lung retransplantation (LR) is a valid choice with a significant risk of perioperative morbidity and mortality in selected patients with graft dysfunction after lung transplantation. Our goal is to analyse our experience in LR in terms of survival and lung function. METHODS: Retrospective study of patients undergoing LR (1990-2019). VARIABLES: recipients and procedure, early mortality, survival and lung function in patients with CLAD. Quantitative variables (mean±SD); qualitative (%). Student's t test or χ2 was used. Survival was estimated using Kaplan-Meier, compared with Log Rank. A p < 0.05 was established as significant. RESULTS: Of 784 transplanted patients, 25 patients (mean age 38.41-16.3 years, 12 men and 13 women) were LR; (CLAD (n = 19), pulmonary infarction (n = 2), airway complications (n = 2), graft dysfunction (n = 1), hyperacute rejection (n = 1), mean time to retransplantation: 5.41 ± 3.87 years in CLAD and 21.2 ± 21.4 days in non-CLAD. The 90-day mortality was 52% and 36.8% in the second period (p = 0.007), being higher in patients who required preoperative ECMO (80 vs. 20%, p = 0.04). The 1- and 5-year survival was 53.9% and 37.7%, respectively (p = 0.016). Survival of the CLAD group was greater (p = 0.08). Pre LR ECMO decreased survival (p = 0.032). After LR, FEV1 improved an average of 0.98 ± 0.13L (25.6 ± 18.8%) (p = 0.001). CONCLUSIONS: LR is a high mortality procedure that requires careful selection of patients with better results in patients with CLAD. The lung function of patients with CLAD improved significantly

Lung retransplant. Experience of a referral centre. / Retrasplante pulmonar. Experiencia de un centro de referencia.

BACKGROUND: Lung retransplantation (LR) is a valid choice with a significant risk of perioperative morbidity and mortality in selected patients with graft dysfunction after lung transplantation. Our goal is to analyse our experience in LR in terms of survival and lung function. METHODS: Retrospective study of patients undergoing LR (1990-2019). VARIABLES: recipients and procedure, early mortality, survival and lung function in patients with CLAD. Quantitative variables (mean±SD); qualitative (%). Student's t test or χ2 was used. Survival was estimated using Kaplan-Meier, compared with Log Rank. A p < 0.05 was established as significant. RESULTS: Of 784 transplanted patients, 25 patients (mean age 38.41-16.3 years, 12 men and 13 women) were LR; (CLAD (n = 19), pulmonary infarction (n = 2), airway complications (n = 2), graft dysfunction (n = 1), hyperacute rejection (n = 1), mean time to retransplantation: 5.41 ± 3.87 years in CLAD and 21.2 ± 21.4 days in non-CLAD. The 90-day mortality was 52% and 36.8% in the second period (p = 0.007), being higher in patients who required preoperative ECMO (80 vs. 20%, p = 0.04). The 1- and 5-year survival was 53.9% and 37.7%, respectively (p = 0.016). Survival of the CLAD group was greater (p = 0.08). Pre LR ECMO decreased survival (p = 0.032). After LR, FEV1 improved an average of 0.98 ± 0.13L (25.6 ± 18.8%) (p = 0.001). CONCLUSIONS: LR is a high mortality procedure that requires careful selection of patients with better results in patients with CLAD. The lung function of patients with CLAD improved significantly.

The heterologous expression of a plastocyanin in the diatom Phaeodactylum tricornutum improves cell growth under iron-deficient conditions.

We have investigated if the heterologous expression of a functional green alga plastocyanin in the diatom Phaeodactylum tricornutum can improve photosynthetic activity and cell growth. Previous in vitro assays showed that a single-mutant of the plastocyanin from the green algae Chlamydomonas reinhardtii is effective in reducing P. tricornutum photosystem I. In this study, in vivo assays with P. tricornutum strains expressing this plastocyanin indicate that even the relatively low intracellular concentrations of holo-plastocyanin detected (≈4 µM) are enough to promote an increased growth (up to 60%) under iron-deficient conditions as compared with the WT strain, measured as higher cell densities, content in pigments and active photosystem I, global photosynthetic rates per cell, and even cell volume. In addition, the presence of plastocyanin as an additional photosynthetic electron carrier seems to decrease the over-reduction of the plastoquinone pool. Consequently, it promotes an improvement in the maximum quantum yield of both photosystem II and I, together with a decrease in the acceptor side photoinhibition of photosystem II-also associated to a reduced oxidative stress-a decrease in the peroxidation of membrane lipids in the choroplast, and a lower degree of limitation on the donor side of photosystem I. Thus the heterologous plastocyanin appears to act as a functional electron carrier, alternative to the native cytochrome c6 , under iron-limiting conditions.

Cannabinoid-induced motor dysfunction via autophagy inhibition.

The recreational and medical use of cannabis is largely increasing worldwide. Cannabis use, however, can cause adverse side effects, so conducting innovative studies aimed to understand and potentially reduce cannabis-evoked harms is important. Previous research conducted on cultured neural cells had supported that CNR1/CB1R (cannabinoid receptor 1), the main molecular target of cannabis, affects macroautophagy/autophagy. However, it was not known whether CNR1 controls autophagy in the brain in vivo, and, eventually, what the functional consequences of a potential CNR1-autophagy connection could be. We have now found that Δ9-tetrahydrocannabinol (THC), the major intoxicating constituent of cannabis, impairs autophagy in the mouse striatum. Administration of autophagy activators (specifically, the rapalog temsirolimus and the disaccharide trehalose) rescues THC-induced autophagy inhibition and motor dyscoordination. The combination of various genetic strategies in vivo supports the idea that CNR1 molecules located on neurons belonging to the direct (striatonigral) pathway are required for the autophagy- and motor-impairing activity of THC. By identifying autophagy as a mechanistic link between THC and motor performance, our findings may open a new conceptual view on how cannabis acts in the brain.

Inhibition of striatonigral autophagy as a link between cannabinoid intoxication and impairment of motor coordination.

The use of cannabis is rapidly expanding worldwide. Thus, innovative studies aimed to identify, understand and potentially reduce cannabis-evoked harms are warranted. Here, we found that Δ9-tetrahydrocannabinol, the psychoactive ingredient of cannabis, disrupts autophagy selectively in the striatum, a brain area that controls motor behavior, both in vitro and in vivo. Boosting autophagy, either pharmacologically (with temsirolimus) or by dietary intervention (with trehalose), rescued the Δ9-tetrahydrocannabinol-induced impairment of motor coordination in mice. The combination of conditional knockout mouse models and viral vector-mediated autophagy-modulating strategies in vivo showed that cannabinoid CB1 receptors located on neurons belonging to the direct (striatonigral) pathway are required for the motor-impairing activity of Δ9-tetrahydrocannabinol by inhibiting local autophagy. Taken together, these findings identify inhibition of autophagy as an unprecedented mechanistic link between cannabinoids and motor performance, and suggest that activators of autophagy might be considered as potential therapeutic tools to treat specific cannabinoid-evoked behavioral alterations.

Endophytic Colonization of Rice (Oryza sativa L.) by the Symbiotic Strain Nostoc punctiforme PCC 73102.

Cyanobacteria are phototrophic microorganisms able to establish nitrogen-fixing symbiotic associations with representatives of all four of the major phylogenetic divisions of terrestrial plants. Despite increasing knowledge on the beneficial effects of cyanobacteria in rice fields, the information about the interaction between these microorganisms and rice at the molecular and structural levels is still limited. We have used the model nitrogen-fixing cyanobacterium Nostoc punctiforme to promote a long-term stable endophytic association with rice. Inoculation with this strain of hydroponic cultures of rice produces a fast adherence of the cyanobacterium to rice roots. At longer times, cyanobacterial growth in the proximity of the roots increased until reaching a plateau. This latter phase coincides with the intracellular colonization of the root epidermis and exodermis. Structural analysis of the roots revealed that the cyanobacterium use an apoplastic route to colonize the plant cells. Moreover, plant roots inoculated with N. punctiforme show both the presence of heterocysts and nitrogenase activity, resulting in the promotion of plant growth under nitrogen deficiency, thus providing benefits for the plant.

A conserved motif in three viral movement proteins from different genera is required for host factor recruitment and cell-to-cell movement.

Due to their minimal genomes, plant viruses are forced to hijack specific cellular pathways to ensure host colonization, a condition that most frequently involves physical interaction between viral and host proteins. Among putative viral interactors are the movement proteins, responsible for plasmodesma gating and genome binding during viral transport. Two of them, DGBp1 and DGBp2, are required for alpha-, beta- and gammacarmovirus cell-to-cell movement, but the number of DGBp-host interactors identified at present is limited. By using two different approaches, yeast two-hybrid and bimolecular fluorescence complementation assays, we found three Arabidopsis factors, eIF3g1, RPP3A and WRKY36, interacting with DGBp1s from each genus mentioned above. eIF3g1 and RPP3A are mainly involved in protein translation initiation and elongation phases, respectively, while WRKY36 belongs to WRKY transcription factor family, important regulators of many defence responses. These host proteins are not expected to be associated with viral movement, but knocking out WRKY36 or silencing either RPP3A or eIF3g1 negatively affected Arabidopsis infection by Turnip crinkle virus. A highly conserved FNF motif at DGBp1 C-terminus was required for protein-protein interaction and cell-to-cell movement, suggesting an important biological role.

A sensitive and rapid RNA silencing suppressor activity assay based on alfalfa mosaic virus expression vector.

Plant viruses express RNA silencing suppressor (RSS) proteins to counteract plant defence mechanisms. Here, we describe a method to assess the RSS activity based on an alfalfa mosaic virus (AMV) RNA 3 expression vector and transgenic Nicotiana tabacum plants that express the P1 and P2 subunits of the AMV replicase (P12 plants). Inoculation of P12 plants with different AMV RNA 3 constructs expressing different HC-Pro mutants that differ in their RSS capabilities, revealed a perfect correlation between necrotic lesions on inoculated leaves and RSS activity. Protoplast analysis showed that the RSS activity correlated with the accumulation of the AMV RNAs. A direct comparison between three RSS activity assays and the AMV-P12 system revealed that the coat protein of carnation mottle virus displays RSS activity with the four assays and reduced the accumulation of the siRNAs.

Key checkpoints in the movement of plant viruses through the host.

Plant viruses cannot exploit any of the membrane fusion-based routes of entry described for animal viruses. In addition, one of the distinctive structures of plant cells, the cell wall, acts as the first barrier against the invasion of pathogens. To overcome the rigidity of the cell wall, plant viruses normally take advantage of the way of life of different biological vectors. Alternatively, the physical damage caused by environmental stresses can facilitate virus entry. Once inside the cell and taking advantage of the characteristic symplastic continuity of plant cells, viruses need to remodel and/or modify the restricted pore size of the plasmodesmata (channels that connect plant cells). In a successful interaction for the virus, it can reach the vascular tissue to systematically invade the plant. The connections between the different cell types in this path are not designed to allow the passage of molecules with the complexity of viruses. During this process, viruses face different cell barriers that must be overcome to reach the distal parts of the plant. In this review, we highlight the current knowledge about how plant RNA viruses enter plant cells, move between them to reach vascular cells and overcome the different physical and cellular barriers that the phloem imposes. Finally, we update the current research on cellular organelles as key regulator checkpoints in the long-distance movement of plant viruses.

The singular properties of photosynthetic cytochrome c550 from the diatom Phaeodactylum tricornutum suggest new alternative functions.

Cytochrome c550 is an extrinsic component in the luminal side of photosystem II (PSII) in cyanobacteria, as well as in eukaryotic algae from the red photosynthetic lineage including, among others, diatoms. We have established that cytochrome c550 from the diatom Phaeodactylum tricornutum can be obtained as a complete protein from the membrane fraction of the alga, although a C-terminal truncated form is purified from the soluble fractions of this diatom as well as from other eukaryotic algae. Eukaryotic cytochromes c550 show distinctive electrostatic features as compared with cyanobacterial cytochrome c550 . In addition, co-immunoseparation and mass spectrometry experiments, as well as immunoelectron microscopy analyses, indicate that although cytochrome c550 from P. tricornutum is mainly located in the thylakoid domain of the chloroplast - where it interacts with PSII - , it can also be found in the chloroplast pyrenoid, related with proteins linked to the CO2 concentrating mechanism and assimilation. These results thus suggest new alternative functions of this heme protein in eukaryotes.

Cytochrome c6 is the main respiratory and photosynthetic soluble electron donor in heterocysts of the cyanobacterium Anabaena sp. PCC 7120.

Cytochrome c6 is a soluble electron carrier, present in all known cyanobacteria, that has been replaced by plastocyanin in plants. Despite their high structural differences, both proteins have been reported to be isofunctional in cyanobacteria and green algae, acting as alternative electron carriers from the cytochrome b6-f complex to photosystem I or terminal oxidases. We have investigated the subcellular localization of both cytochrome c6 and plastocyanin in the heterocyst-forming cyanobacterium Anabaena sp. PCC 7120 grown in the presence of combined nitrogen and under diazotrophic conditions. Our studies conclude that cytochrome c6 is expressed at significant levels in heterocysts, even in the presence of copper, condition in which it is strongly repressed in vegetative cells. However, the copper-dependent regulation of plastocyanin is not altered in heterocysts. In addition, in heterocysts, cytochrome c6 has shown to be the main soluble electron carrier to cytochrome c oxidase-2 in respiration. A cytochrome c6 deletion mutant is unable to grow under diazotrophic conditions in the presence of copper, suggesting that cytochrome c6 plays an essential role in the physiology of heterocysts that cannot be covered by plastocyanin.