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Reproductive Biology of Diatoms (in Russ. Репродуктивная биология диатомовых водорослей)
Abstract
The monograph concerns items related to reproductive biology of diatoms including such sections as sex and principles of sex determination in diatoms, their life cycles, patterns of sexual reproduction, sex distribution and mating systems, factors inducing sexual reproduction, inheritance coupled with sex, reproductive boundaries and distribution of diatoms, phylogeny of diatoms in the light of reproductive characteristics, etc. The book is dedicated for specialists in algology, hydrobiolody, reproductive biology; for students and graduate students in the relevant areas of study. (in Russian)
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Род Entomoneis Ehrenberg, 1845 достаточно богат видами. Недооценённое разнообразие Entomoneis требует более глубокого морфологического и молекулярного исследования этого рода, а также изучения эколого-физиологических характеристик видов, в частности пределов толерантности к факторам среды. Учитывая распространение видов Entomoneis в водоёмах с различной солёностью, мы поставили задачу исследовать пределы толерантности и установить оптимальную солёность для вегетативного размножения и полового воспроизведения диатомовой водоросли Entomoneis sp. из Чёрного моря. В работе использованы оказавшиеся репродуктивно совместимыми клоновые культуры, которые были выделены из проб, отобранных у крымского и турецкого побережий Чёрного моря. Для клона Entomoneis sp. 7.0906-D получена нуклеотидная последовательность гена rbcL, которая представлена в базе данных GenBank под номером MT424817. Использованный в экспериментах вид хотя и напоминает по морфологическим критериям E. paludosa, но, по молекулярным данным, далеко отстоит от такового и по эколого-физиологическим характеристикам является морским видом. Согласно литературным материалам, E. paludosa, в отличие от изученного нами Entomoneis sp., обитает в солоноватых, слабосолёных и даже пресных водоёмах. Эксперименты по изучению пределов галотолерантности показали, что черноморские клоны Entomoneis sp. жизнеспособны в диапазоне, охватывающем как минимум 40 ‰ (от 8 до 48 ‰). Диапазон солёности среды, в котором Entomoneis sp. способен к половому воспроизведению, значительно ýже и находится в пределах от 18 до 36 ‰. Определены оптимальные значения солёности для вегетативного роста и для полового воспроизведения (27,4 и 26,4 ‰ соответственно), оказавшиеся в обоих случаях выше тех значений, при которых вид обитает в природе. У Entomoneis sp. по мере увеличения солёности среды отмечена тенденция к уменьшению размеров инициальных клеток, образующихся в результате полового
The focus of this study was to determine the mating type of Schizostauron trachyderma and examine the relationship between cell size (life cycle), lipid droplet size, and lipid content among diatoms with similar cell dimensions. To accomplish that, we have chosen monoclonal cultures of two closely related diatom species, namely S. trachyderma and S. rawaii . In a series of experiments, we successfully induced sexual reproduction within S. trachyderma strains to reconstruct the whole cell cycle involving cells of the maximum (initial cells) and minimum viable size for a given species. The mating-type and sexual reproduction stages were described and documented. A unique experimental setting involved initial cell isolation and their lipid droplet examination using flow cytometry and confocal microscopy after Nile Red staining. The results of the series of experiments indicate correlations between cell size, the number of neutral lipids per cell, and the size of lipid droplets, suggesting that cell capacity for lipid accumulation is dependent on their position in the life cycle.
Репродуктивное поведение диатомовых водорослей занимает умы исследователей немногим более 170 лет. За это сравнительно небольшое время установлен ряд общих закономерностей и правил, согласно которым происходит зависящее от размеров клеток прохождение жизненного цикла. Описан половой процесс у порядка 250 видов диатомовых. В работе обсуждаются предложенные в разное время варианты классификации типов полового процесса. Показано, что эволюция диатомовых тесно связана с эволюцией способов доставки гамет к месту сингамии. Изменение репродуктивного поведения рассматривается у диатомовых как один из основных эволюционных трендов. Выделены наиболее значимые в последние десятилетия направления исследований в области репродуктивной биологии диатомовых.
Benthic diatoms dominate primary production in marine subtidal and intertidal environments. Their extraordinary species diversity and ecological success is thought to be linked with their predominantly heterothallic sexual reproduction. Little is known about pheromone involvement during mating of pennate diatoms. Here we describe pheromone guided mating in the coastal raphid diatom Cylindrotheca closterium . We show that the two mating types (mt ⁺ and mt ⁻ ) have distinct functions. Similar to other benthic diatoms, mt ⁺ cells are searching for the mt ⁻ cells to pair. To enhance mating efficiency mt ⁻ exudes an attraction pheromone which we proved by establishing a novel capillary assay. Further, two more pheromones produced by mt ⁻ promote the sexual events. One arrests the cell cycle progression of mt ⁺ while the other induces gametogenesis of mt ⁺ . We suggest that C. closterium shares a functionally similar pheromone system with other pennate diatoms like S eminavis robusta and Pseudostaurosira trainorii which synchronize sexual events and mate attraction. Remarkably, we found no evidence of mt ⁺ producing pheromones, which differentiates C. closterium from other pennates and suggests a less complex pheromone system in C. closterium .
Specimens of a new species of blue diatoms from the genus Haslea Simonsen were discovered in geographically distant sampling sites, first in the Canary Archipelago, then North Carolina, Gulf of Naples, the Croatian South Adriatic Sea, and Turkish coast of the Eastern Mediterranean Sea. An exhaustive characterization of these specimens, using a combined morphological and genomic approach led to the conclusion that they belong to a single new to science cosmopolitan species, Haslea silbo sp. nov. A preliminary characterization of its blue pigment shows similarities to marennine produced by Haslea ostrearia, as evidenced by UV–visible spectrophotometry and Raman spectrometry. Life cycle stages including auxosporulation were also observed, providing data on the cardinal points of this species. For the two most geographically distant populations (North Carolina and East Mediterranean), complete mitochondrial and plastid genomes were sequenced. The mitogenomes of both strains share a rare atp6 pseudogene, but the number, nature, and positions of the group II introns inside its cox1 gene differ between the two populations. There are also two pairs of genes fused in single ORFs. The plastid genomes are characterized by large regions of recombination with plasmid DNA, which are in both cases located between the ycf35 and psbA genes, but whose content differs between the strains. The two sequenced strains hosts three plasmids coding for putative serine recombinase protein whose sequences are compared, and four out of six of these plasmids were highly conserved.
Diatoms belonging to the family Epithemiaceae have endosymbiont ‘spheroid bodies’, which have received attention as a model to provide new insights into the early stages of organelle evolution. Uniparental organelle inheritance, known in a wide range of sexually reproducing eukaryotes, is considered to be one of the key characteristics acquired during the evolution of an endosymbiont into an organelle. However, there has been no information about the inheritance of spheroid bodies. The aim of the present study was, therefore, to investigate the inheritance modes of the spheroid bodies and plastids in the isogamous diatom Epithemia gibba var. ventricosa, which we established to be heterothallic. We induced sexual reproduction of E. gibba var. ventricosa in culture, using sexually compatible mating strains that differed with respect to nucleotide polymorphisms in the spheroid body and the plastid genomes. The F1 strains were genotyped to reveal the parental origin of the spheroid bodies and plastids using parent-specific polymorphisms. The results suggested that inheritance of the spheroid bodies was uniparental (i.e. progeny have the spheroid body genome from either parent but not both) and random (i.e. with an unbiased ratio of parental origins), while that of the plastids was more complex, being predominantly uniparental but with a few biparental cases. This study is the first to report the inheritance pattern of the spheroid body and will contribute to better understand the evolutionary state of this organelle.
The cosmopolitan, species-rich diatom genus Pseudo-nitzschia represents a good system for the study of speciation, evolution and diversity. Understanding elements linked to population dynamics and life cycle regulation for these species is of particular importance in view of their ability to produce the toxin domoic acid and cause harmful blooms. Pseudo-nitzschia multistriata, one of the toxic species that represents a model for the study of life cycle related questions, is the only diatom for which a sex determination mechanism has been described. Populations in the Gulf of Naples (Mediterranean Sea), can share four different allelic variants (A, M, B, N) of the mating type determination region, and one of them (A) is responsible for the determination of the mating type + (MT+), defined by the MT+ restricted expression of the gene MRP3. Here, we analysed the sex determination genomic region in three new strains isolated from the Gulf of Mexico and compared it to the alleles previously described in the Mediterranean strains. We first show that these geographically distant strains of P. multistriata belong to different populations but can interbreed. Next, we show that the two populations share an overall similar structure of the genomic locus although differences can be seen in the polymorphic regions upstream of MRP3. In strain P4-C1, we amplified and sequenced an allele (M) identical to one of those previously characterized in the Mediterranean strains. In the other two strains, P4-C2 and P4-C5, we identified three new alleles, which we named A2, B2 and N2. P4-C2 and P4-C5 are heterozygous and share the common allele A2 linked to the monoallelic expression of the MT+ specific sex determining gene MRP3. Our results expand information on the global distribution of P. multistriata and on the level of conservation of the sex determination region in different populations. The definition of the extent of intra- and inter-specific conservation of this region would be a relevant addition to our understanding of Pseudo-nitzschia diversity and evolution.