FtsZ of filamentous, heterocyst-forming cyanobacteria has a conserved N-Terminal peptide required for normal FtsZ polymerization and cell division

Filamentous cyanobacteria grow by intercalary cell division, which should involve distinct steps compared to those producing separate daughter cells. The N-terminal region of FtsZ is highly conserved in the clade of filamentous cyanobacteria capable of cell differentiation. A derivative of the model strain Anabaena sp. PCC 7120 expressing only an FtsZ lacking the amino acids 2-51 of the N-terminal peptide (1N-FtsZ) could not be segregated. Strain CSL110 expresses both 1N-FtsZ, from the endogenous ftsZ gene promoter, and the native FtsZ from a synthetic regulated promoter. Under conditions of 1N-FtsZ predominance, cells of strain CSL110 progressively enlarge, reflecting reduced cell division, and show instances of asymmetric cell division and aberrant Z-structures notably differing from the Z-ring formed by FtsZ in the wild type. In bacterial 2-hybrid assays FtsZ interacted with 1N-FtsZ. However, 1N-FtsZ-GFP appeared impaired for incorporation into Z-rings when expressed together with FtsZ. FtsZ, but not 1N-FtsZ, interacted with the essential protein SepF. Both FtsZ and 1N-FtsZ polymerize in vitro exhibiting comparable GTPase activities. However, filaments of FtsZ show a distinct curling forming toroids, whereas 1N-FtsZ form thick bundles of straight filaments. Thus, the N-terminal FtsZ sequence appears to contribute to a distinct FtsZ polymerization mode that is essential for cell division and division plane location in Anabaena.Agencia Estatal de Investigación BFU2013-44686-P BFU2016-77097-

Pre-service Teacher-Generated Analogies for Biology Concepts: Implications for Teacher Training

[Resumen] Las analogías son potentes recursos que favorecen el aprendizaje activo. Sin embargo, la investigación en didáctica de las ciencias ha mostrado que la mayoría de los docentes en activo emplea pocas analogías o analogías inconsistentes. Este hecho podría tener su origen durante la formación de maestros, aunque es una línea de investigación aún por explorar. En este trabajo se presenta un estudio exploratorio en el que se analizan las analogías diseñadas por 231 maestros en formación, para una serie de contenidos biológicos impartidos a lo largo de Educación Primaria. La mayoría de los participantes no son capaces de plantear análogos apropiados, sobre todo para los blancos más abstractos como célula, respuesta inmune o impulso nervioso. Asimismo, se detecta confusión de las analogías con los ejemplos y las experiencias prácticas. En base a estos resultados, se concluye que la formación inicial proporcionada a los participantes no es suficiente para implementar analogías como recurso didáctico en Biología.[Abstract] Analogies are an effective strategy for active learning. Nevertheless, research in science education shows that most teachers use analogies on an irregular or inconsistent basis, possibly owing to a lack of targeted training at the pre-service level. This article presents an exploratory study of this overlooked line of research, based on an analysis of the analogies proposed by 231 pre-service primary teachers for a selection of biology concepts taught at different stages of the primary school curriculum. The results showed that most of the participants were unable to formulate appropriate analogies, especially for more abstract concepts, such as cells, immune response or nerve impulse transmission. The study also observed a tendency to mix analogies with examples and practical experiences. The findings indicate that primary education students are insufficiently prepared by their teacher training to use analogies as a teaching and learning strategy for the biology curriculum.Este estudio ha sido financiado por el Proyecto EDU2016-77007-R (Ministerio de Ciencia e Innovación) y por la Ayuda a Grupos GR18004 (Junta de Extremadura)Junta de Extremadura; GR1800

Trans-oligomerization of duplicated aminoacyl-tRNA synthetases maintains genetic code fidelity under stress

Aminoacyl-tRNA synthetases (aaRSs) play a key role in deciphering the genetic message by producing charged tRNAs and are equipped with proofreading mechanisms to ensure correct pairing of tRNAs with their cognate amino acid. Duplicated aaRSs are very frequent in Nature, with 25,913 cases observed in 26,837 genomes. The oligomeric nature of many aaRSs raises the question of how the functioning and oligomerization of duplicated enzymes is organized. We characterized this issue in a model prokaryotic organism that expresses two different threonyl-tRNA synthetases, responsible for Thr-tRNAThr synthesis: one accurate and constitutively expressed (T1) and another (T2) with impaired proofreading activity that also generates mischarged Ser-tRNAThr. Low zinc promotes dissociation of dimeric T1 into monomers deprived of aminoacylation activity and simultaneous induction of T2, which is active for aminoacylation under low zinc. T2 either forms homodimers or heterodimerizes with T1 subunits that provide essential proofreading activity in trans. These findings evidence that in organisms with duplicated genes, cells can orchestrate the assemblage of aaRSs oligomers that meet the necessities of the cell in each situation. We propose that controlled oligomerization of duplicated aaRSs is an adaptive mechanism that can potentially be expanded to the plethora of organisms with duplicated oligomeric aaRSs.Ministerio de Economía y Competitividad BFU2010–19544, BFU2013–44686-

The plastid ancestor originated among one of the major cyanobacterial lineages

The primary endosymbiotic origin of chloroplasts is now well established but the identification of the present cyanobacteria most closely related to the plastid ancestor remains debated. We analyse the evolutionary trajectory of a subset of highly conserved cyanobacterial proteins (core) along the plastid lineage, those which were not lost after the endosymbiosis. We concatenate the sequences of 33 cyanobacterial core proteins that share a congruent evolutionary history, with their eukaryotic counterparts to reconstruct their phylogeny using sophisticated evolutionary models. We perform an independent reconstruction using concatenated 16S and 23S rRNA sequences. These complementary approaches converge to a plastid origin occurring during the divergence of one of the major cyanobacterial lineages that include N2-fixing filamentous cyanobacteria and species able to differentiate heterocysts