Males evolved from the dominant isogametic mating type.
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Algal Proteins↗
Biomedical subjects
Tsuneyoshi Kuroiwa
Publications and source records attributed to Tsuneyoshi Kuroiwa.
Isolated chloroplast division machinery can actively constrict after stretching.
Chloroplast division involves plastid-dividing, dynamin, and FtsZ (PDF) rings. We isolated intact supertwisted (or spiral) and circular PDF machineries from chloroplasts of the red alga Cyanidioschyzon merolae. After individual intact PDF machineries were stretched to four times their original lengths with optical tweezers, they spontaneously returned to their original sizes. Dynamin-released PDF machineries did not retain the spiral structure and could not be stretched. Thus, dynamin may generate the motive force for contraction by filament sliding in dividing chloroplasts, in addition to pinching-off the membranes.
Actin Cytoskeleton↗
Species preferentiality of the pollen tube attractant derived from the synergid cell of Torenia fournieri.
The synergid cell of Torenia fournieri attracts pollen tubes by a diffusible but yet unknown chemical attractant. Here we investigated the species difference of the attractant using five closely related species in two genera, namely T. fournieri, Torenia baillonii, Torenia concolor, Lindernia (Vandellia) crustacea, and Lindernia micrantha. These five species have an exserted embryo sac, and ablation experiments confirmed that their synergid cells attracted the pollen tube. When ovules of T. fournieri and one of the other species were cultivated together with pollen tubes of each species, pollen tubes were significantly more attracted to synergid cells of the corresponding species. The attraction was not affected by the close proximity of embryo sacs of different species. This suggests that the attractant is a species-preferential molecule that is likely synthesized in the synergid cell. The calcium ion, long considered a potential attractant, could not serve as the sole attractant in these species, because elevation of the calcium ion concentration did not affect the observed attraction. In vivo crossing experiments also showed that the attraction of the pollen tube to the embryo sac was impaired when pollen tubes of different species arrived around the embryo sac, suggesting that the species preferentiality of the attractant may serve as a reproductive barrier in the final step of directional control of the pollen tube.
Biological Factors↗
Structure, function and evolution of the mitochondrial division apparatus.
Mitochondria are derived from free-living alpha-proteobacteria that were engulfed by eukaryotic host cells through the process of endosymbiosis, and therefore have their own DNA which is organized using basic proteins to form organelle nuclei (nucleoids). Mitochondria divide and are split amongst the daughter cells during cell proliferation. Their division can be separated into two main events: division of the mitochondrial nuclei and division of the matrix (the so-called mitochondrial division, or mitochondriokinesis). In this review, we first focus on the cytogenetical relationships between mitochondrial nuclear division and mitochondriokinesis. Mitochondriokinesis occurs after mitochondrial nuclear division, similar to bacterial cytokinesis. We then describe the fine structure and dynamics of the mitochondrial division ring (MD ring) as a basic morphological background for mitochondriokinesis. Electron microscopy studies first identified a small electron-dense MD ring in the cytoplasm at the constriction sites of dividing mitochondria in the slime mold Physarum polycephalum, and then two large MD rings (with outer cytoplasmic and inner matrix sides) in the red alga Cyanidioschyzon merolae. Now MD rings have been found in all eukaryotes. In the third section, we describe the relationships between the MD ring and the FtsZ ring descended from ancestral bacteria. Other than the GTPase, FtsZ, mitochondria have lost most of the proteins required for bacterial cytokinesis as a consequence of endosymbiosis. The FtsZ protein forms an electron transparent ring (FtsZ or Z ring) in the matrix inside the inner MD ring. For the fourth section, we describe the dynamic association between the outer MD ring with a ring composed of the eukaryote-specific GTPase dynamin. Recent studies have revealed that eukaryote-specific GTPase dynamins form an electron transparent ring between the outer membrane and the MD ring. Thus, mitochondriokinesis is thought to be controlled by a mitochondrial division (MD) apparatus including a dynamic trio, namely the FtsZ, MD and dynamin rings, which consist of a chimera of rings from bacteria and eukaryotes in primitive organisms. Since the genes for the MD ring and dynamin rings are not found in the prokaryotic genome, the host genomes may make these rings to actively control mitochondrial division. In the fifth part, we focus on the dynamic changes in the formation and disassembly of the FtsZ, MD and dynamin rings. FtsZ rings are digested during a later period of mitochondrial division and then finally the MD and dynamin ring apparatuses pinched off the daughter mitochondria, supporting the idea that the host genomes are responsible for the ultimate control of mitochondrial division. We discuss the evolution, from the original vesicle division (VD) apparatuses to VD apparatuses including classical dynamin rings and MD apparatuses. It is likely that the MD apparatuses involving the dynamic trio evolved into the plastid division (PD) apparatus in Bikonta, while in Opisthokonta, the MD apparatus was simplified during evolution and may have branched into the mitochondrial fusion apparatus. Finally, we describe the possibility of intact isolation of large MD/PD apparatuses, the identification of all their proteins and their related genes using C. merolae genome information and TOF-MS analyses. These results will assist in elucidating the universal mechanism and evolution of MD, PD and VD apparatuses.
Animals↗
Active digestion of sperm mitochondrial DNA in single living sperm revealed by optical tweezers.
In almost all eukaryotes, mitochondrial (mt) genes are transmitted to progeny mainly from the maternal parent. The most popular explanation for this phenomenon is simple dilution of paternal mtDNA, because the paternal gametes (sperm) are much smaller than maternal gametes (egg) and contribute a limited amount of mitochondria to the progeny. Recently, this simple explanation has been challenged in several reports that describe the active digestion of sperm mtDNA, down-regulation of mtDNA replication in sperm, and proteolysis of mitochondria triggered by ubiquitination. In this investigation, we visualized mt nucleoids in living sperm by using highly sensitive SYBR green I vital staining. The ability to visualize mt nucleoids allowed us to clarify that the elimination of sperm mtDNA upon fertilization is achieved through two steps: (i) gradual decrease of mt nucleoid numbers during spermatogenesis and (ii) rapid digestion of sperm mtDNA just after fertilization. One notable point is that the digestion of mtDNA is achieved before the complete destruction of mitochondrial structures, which may be necessary to avoid the diffusion and transmission of potentially deleterious sperm mtDNA to the progeny.
Animals↗
GENERATIVE CELL SPECIFIC 1 is essential for angiosperm fertilization.
The double fertilization process in angiosperms is based on the delivery of a pair of sperm cells by the pollen tube (the male gametophyte), which elongates towards an embryo sac (the female gametophyte) enclosing an egg and a central cell. Several studies have described the mechanisms of gametophyte interaction, and also the fertilization process - from pollination to pollen tube acceptance. However, the mechanisms of gamete interaction are not fully understood. Cytological studies have shown that male gametes possess distinct cell-surface structures and genes specific to male gametes have been detected in cDNA libraries. Thus, studies of isolated gametes may offer clues to understanding the sperm-egg interaction. In this study, we identified a novel protein, designated GCS1 (GENERATIVE CELL SPECIFIC 1), using generative cells isolated from Lilium longiflorum pollen. GCS1 possesses a carboxy-terminal transmembrane domain, and homologues are present in various species, including non-angiosperms. Immunological assays indicate that GCS1 is accumulated during late gametogenesis and is localized on the plasma membrane of generative cells. In addition, Arabidopsis thaliana GCS1 mutant gametes fail to fuse, resulting in male sterility and suggesting that GCS1 is a critical fertilization factor in angiosperms.
Amino Acid Sequence↗
Cell cycle-regulated, microtubule-independent organelle division in Cyanidioschyzon merolae.
Mitochondrial and chloroplast division controls the number and morphology of organelles, but how cells regulate organelle division remains to be clarified. Here, we show that each step of mitochondrial and chloroplast division is closely associated with the cell cycle in Cyanidioschyzon merolae. Electron microscopy revealed direct associations between the spindle pole bodies and mitochondria, suggesting that mitochondrial distribution is physically coupled with mitosis. Interconnected organelles were fractionated under microtubule-stabilizing condition. Immunoblotting analysis revealed that the protein levels required for organelle division increased before microtubule changes upon cell division, indicating that regulation of protein expression for organelle division is distinct from that of cytokinesis. At the mitochondrial division site, dynamin stuck to one of the divided mitochondria and was spatially associated with the tip of a microtubule stretching from the other one. Inhibition of microtubule organization, proteasome activity or DNA synthesis, respectively, induced arrested cells with divided but shrunk mitochondria, with divided and segregated mitochondria, or with incomplete mitochondrial division restrained at the final severance, and repetitive chloroplast division. The results indicated that mitochondrial morphology and segregation but not division depend on microtubules and implied that the division processes of the two organelles are regulated at distinct checkpoints.
Algal Proteins↗
Cyanidioschyzon merolae genome. A tool for facilitating comparable studies on organelle biogenesis in photosynthetic eukaryotes.
The ultrasmall unicellular red alga Cyanidioschyzon merolae lives in the extreme environment of acidic hot springs and is thought to retain primitive features of cellular and genome organization. We determined the 16.5-Mb nuclear genome sequence of C. merolae 10D as the first complete algal genome. BLASTs and annotation results showed that C. merolae has a mixed gene repertoire of plants and animals, also implying a relationship with prokaryotes, although its photosynthetic components were comparable to other phototrophs. The unicellular green alga Chlamydomonas reinhardtii has been used as a model system for molecular biology research on, for example, photosynthesis, motility, and sexual reproduction. Though both algae are unicellular, the genome size, number of organelles, and surface structures are remarkably different. Here, we report the characteristics of double membrane- and single membrane-bound organelles and their related genes in C. merolae and conduct comparative analyses of predicted protein sequences encoded by the genomes of C. merolae and C. reinhardtii. We examine the predicted proteins of both algae by reciprocal BLASTP analysis, KOG assignment, and gene annotation. The results suggest that most core biological functions are carried out by orthologous proteins that occur in comparable numbers. Although the fundamental gene organizations resembled each other, the genes for organization of chromatin, cytoskeletal components, and flagellar movement remarkably increased in C. reinhardtii. Molecular phylogenetic analyses suggested that the tubulin is close to plant tubulin rather than that of animals and fungi. These results reflect the increase in genome size, the acquisition of complicated cellular structures, and kinematic devices in C. reinhardtii.
Algal Proteins↗
[Mechanism of mitochondrial and plastid divisions: memory of 3 genome sequences of Cyanidioschyzon merolae as an origin of enkaryote].
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Arabidopsis Proteins↗
[Chloroplast division machinery and its evolution].
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Arabidopsis Proteins↗
[Mechanism of origin and evolution of eukaryote on basis of genome analysis of a red alga Cyanidioschyzon merolae].
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Cytokinesis↗
The minimal eukaryotic ribosomal DNA units in the primitive red alga Cyanidioschyzon merolae.
Cyanidioschyzon merolae is a small unicellular red alga that is considered to belong to one of the most deeply branched taxa in the plant kingdom. Its genome size is estimated to be 16.5 Mbp, one of the smallest among free-living eukaryotes. In the nucleus containing this small genome, one nucleolus is clearly observed, but the molecular basis for the intranuclear structure including ribosomal DNA organization is still unclear. We constructed a bacterial artificial chromosome library for C. merolae 10D composed of two subsets with different insert size distributions. The two subsets have average insert sizes of 97 and 48 kb, representing 10.0- and 6.9-fold genome-equivalent coverage of the haploid genome, respectively. For application to whole-genome shotgun sequencing, the termini of each clone were sequenced as sequence-tagged connectors and mapped on the contigs assigned to chromosomes. Screening for rRNA genes by conventional colony hybridization with high-density filter blots and subsequent sequencing revealed that the C. merolae genome contained the smallest number of ribosomal DNA units among all the eukaryotes examined to date. They consist of only 3 single units of rRNA genes distributed on separate chromosomal loci, representing an implication for concerted evolution. Based on these results, the origin and evolution of the nucleolus are discussed.
Base Sequence↗
Genome sequence of the ultrasmall unicellular red alga Cyanidioschyzon merolae 10D.
Small, compact genomes of ultrasmall unicellular algae provide information on the basic and essential genes that support the lives of photosynthetic eukaryotes, including higher plants. Here we report the 16,520,305-base-pair sequence of the 20 chromosomes of the unicellular red alga Cyanidioschyzon merolae 10D as the first complete algal genome. We identified 5,331 genes in total, of which at least 86.3% were expressed. Unique characteristics of this genomic structure include: a lack of introns in all but 26 genes; only three copies of ribosomal DNA units that maintain the nucleolus; and two dynamin genes that are involved only in the division of mitochondria and plastids. The conserved mosaic origin of Calvin cycle enzymes in this red alga and in green plants supports the hypothesis of the existence of single primary plastid endosymbiosis. The lack of a myosin gene, in addition to the unexpressed actin gene, suggests a simpler system of cytokinesis. These results indicate that the C. merolae genome provides a model system with a simple gene composition for studying the origin, evolution and fundamental mechanisms of eukaryotic cells.
Actins↗
Two types of FtsZ proteins in mitochondria and red-lineage chloroplasts: the duplication of FtsZ is implicated in endosymbiosis.
The ancestors of plastids and mitochondria were once free-living bacteria that became organelles as a result of endosymbiosis. According to this theory, a key bacterial division protein, FtsZ, plays a role in plastid division in algae and plants as well as in mitochondrial division in lower eukaryotes. Recent studies have shown that organelle division is a process that combines features derived from the bacterial division system with features contributed by host eukaryotic cells. Two nonredundant versions of FtsZ, FtsZ1 and FtsZ2, have been identified in green-lineage plastids, whereas most bacteria have a single ftsZ gene. To examine whether there is also more than one type of FtsZ in red-lineage chloroplasts (red algal chloroplasts and chloroplasts that originated from the secondary endosymbiosis of red algae) and in mitochondria, we obtained FtsZ sequences from the complete sequence of the primitive red alga Cyanidioschyzon merolae and the draft sequence of the stramenopile (heterokont) Thalassiosira pseudonana. Phylogenetic analyses that included known FtsZ proteins identified two types of chloroplast FtsZ in red algae (FtsZA and FtsZB) and stramenopiles (FtsZA and FtsZC). These analyses also showed that FtsZB emerged after the red and green lineages diverged, while FtsZC arose by the duplication of an ftsZA gene that in turn descended from a red alga engulfed by the ancestor of stramenopiles. A comparison of the predicted proteins showed that like bacterial FtsZ and green-lineage FtsZ2, FtsZA has a short conserved C-termmal sequence (the C-terminal core domain), whereas FtsZB and FtsZC, like the green-lineage FtsZ1, lack this sequence. In addition, the Cyanidioschyzon and Dictyostelium genomes encode two types of mitochondrial FtsZ proteins, one of which lacks the C-terminal variable domain. These results suggest that the acquisition of an additional FtsZ protein with a modified C terminus was common to the primary and secondary endosymbioses that produced plastids and that this also occurred during the establishment of mitochondria, presumably to regulate the multiplication of these organelles.
Algal Proteins↗
Cyanobacterial genes transmitted to the nucleus before divergence of red algae in the Chromista.
The plastids of red algae, green plants, and glaucophytes may have originated directly from a cyanobacterium-like prokaryote via primary endosymbiosis. In contrast, the plastids of other lineages of eukaryotic phototrophs appear to be the result of secondary or tertiary endosymbiotic events involving a phototrophic eukaryote and a eukaryotic host cell. Although phylogenetic analyses of multiple plastid genes from a wide range of eukaryotic lineages have been carried out, the phylogenetic positions of the secondary plastids of the Chromista (Heterokontophyta, Haptophyta and Cryptophyta) are ambiguous in a range of different analyses. This ambiguity may be the result of unusual substitutions or bias in the plastid genes established by the secondary endosymbiosis. In this study, we carried out phylogenetic analyses of five nuclear genes of cyanobacterial origin (6-phosphogluconate dehydrogenase [gnd], oxygen-evolving-enhancer [psbO], phosphoglycerate kinase [pgk], delta-aminolevulinic acid dehydratase [aladh], and ATP synthase gamma [atpC] genes), using the genome sequence data from the primitive red alga Cyanidioschyzon merolae 10D. The sequence data robustly resolved the origin of the cyanobacterial genes in the nuclei of the Chromista (Heterokontophyta and Haptophyta) and Dinophyta, before the divergence of the extant red algae (including Porphyra [Rhodophyceae] and Cyanidioschyzon [Cyadidiophyceae]). Although it is likely that gnd genes in the Chromista were transmitted from the cyanobacterium-like ancestor of plastids in the primary endosymbiosis, other genes might have been transferred from nuclei of a red algal ancestor in the secondary endosymbiosis. Therefore, the results indicate that the Chromista might have originated from the ancient secondary endosymbiosis before the divergence of extant red algae.
Base Sequence↗
Organelle nuclei in higher plants: structure, composition, function, and evolution.
Plant cells have two distinct types of energy-converting organelles: plastids and mitochondria. These organelles have their own DNAs and are regarded as descendants of endosymbiotic prokaryotes. The organelle DNAs associate with various proteins to form compact DNA-protein complexes, which are referred to as organelle nuclei or nucleoids. Various functions of organelle genomes, such as DNA replication and transcription, are performed within these compact structures. Fluorescence microscopy using the DNA-specific fluorochrome 4',6-diamidino-2-phenylindole has played a pivotal role in establishing the concept of "organelle nuclei." This fluorochrome has also facilitated the isolation of morphologically intact organelle nuclei, which is indispensable for understanding their structure and composition. Moreover, development of an in vitro transcription?DNA synthesis system using isolated organelle nuclei has provided us with a means of measuring and analyzing the function of organelle nuclei. In addition to these morphological and biochemical approaches, genomics has also had a great impact on our ability to investigate the components of organelle nuclei. These analyses have revealed that organelle nuclei are not a vestige of the bacterial counterpart, but rather are a complex system established through extensive interaction between organelle and cell nuclear genomes during evolution. Extensive diversion or exchange during evolution is predicted to have occurred for several important structural proteins, such as major DNA-compacting proteins, and functional proteins, such as RNA and DNA polymerases, resulting in complex mechanisms to control the function of organelle genomes. Thus, organelle nuclei represent the most dynamic front of interaction between the three genomes (cell nuclear, plastid, and mitochondrial) constituting eukaryotic plant cells.
Cell Nucleus↗
Improvement of culture conditions and evidence for nuclear transformation by homologous recombination in a red alga, Cyanidioschyzon merolae 10D.
Although the nuclear genome sequence of Cyanidioschyzon merolae 10D, a unicellular red alga, was recently determined, DNA transformation technology that is important as a model plant system has never been available thus far. In this study, improved culture conditions resulted in a faster growth rate of C. merolae in liquid medium (doubling time = 9.2 h), and colony formation on gellan gum plates. Using these conditions, spontaneous mutants (5-fluoroortic acid resistant) deficient in the UMP synthase gene were isolated. The lesions were then restored by introducing the wild-type UMP synthase gene into the cells suggesting DNA transformation by homologous recombination.
Amino Acid Sequence↗
Triple immunofluorescent labeling of FtsZ, dynamin, and EF-Tu reveals a loose association between the inner and outer membrane mitochondrial division machinery in the red alga Cyanidioschyzon merolae.
In the mitochondria of primitive eukaryotes, FtsZ and dynamin are part of the machinery involved in division of the inner and outer membranes, respectively. These genes also commonly function in the same manner during chloroplast division. In this study, a relationship between the localization of the inner and outer division machinery was directly shown for the first time. Triple immunofluorescent labeling was performed in the red alga Cyanidioschyzon merolae by a device using narrow bandpass filter sets and bright photostable dyes. FtsZ (CmFtsZ1) and dynamin (CmDnm1) localizations were examined simultaneously throughout the mitochondrial division cycle with an alternative mitochondrial marker protein, the mitochondrial translation elongation factor EF-Tu, whose localization was also shown to be identical to the mitochondrial matrix. FtsZ and dynamin did not necessarily co-localize when both were recruited to the mitochondrial constriction site, indicating that inner and outer dividing machineries are not in tight association during the late stage of division.
Bacterial Proteins↗