A fusion protein of polyphosphate kinase 1 (PPK1) and a Nudix hydrolase is involved in inorganic polyphosphate accumulation in the unicellular red alga Cyanidioschyzon merolae.

Inorganic polyphosphate (polyP) is a linear polymer of phosphate that plays various roles in cells, including in phosphate and metal homeostasis. Homologs of the vacuolar transporter chaperone 4 (VTC4), catalyzing polyP synthesis in many eukaryotes, are absent in red algae, which are among the earliest divergent plant lineages. We identified homologs of polyphosphate kinase 1 (PPK1), a conserved polyP synthase in bacteria, in 42 eukaryotic genomes, including 31 species detected in this study and 12 species of red algae.

Complete mitochondrial and chloroplast DNA sequences of the freshwater green microalga Medakamo hakoo.

We report the complete organellar genome sequences of an ultrasmall green alga, Medakamo hakoo strain M-hakoo 311, which has the smallest known nuclear genome in freshwater green algae. Medakamo hakoo has 90.8-kb chloroplast and 36.

Genomic analysis of an ultrasmall freshwater green alga, Medakamo hakoo.

Ultrasmall algae have attracted the attention of biologists investigating the basic mechanisms underlying living systems. Their potential as effective organisms for producing useful substances is also of interest in bioindustry. Although genomic information is indispensable for elucidating metabolism and promoting molecular breeding, many ultrasmall algae remain genetically uncharacterized.

Existence of giant mitochondria-containing sheet structures lacking cristae and matrix in the etiolated cotyledon of Arabidopsis thaliana.

Mitochondria are essential organelles involved in the production and supply of energy in eukaryotic cells. Recently, the use of serial section scanning electron microscopy (SEM) has allowed accurate three-dimensional (3D) reconstructed images of even complex organelle structures. Using this method, ultrathin sections of etiolated cotyledons were observed 4 days after germination of Arabidopsis thaliana in the dark, and giant mitochondria were found.

ESCRT Machinery Mediates Cytokinetic Abscission in the Unicellular Red Alga .

In many eukaryotes, cytokinesis proceeds in two successive steps: first, ingression of the cleavage furrow and second, abscission of the intercellular bridge. In animal cells, the actomyosin contractile ring is involved in the first step, while the endosomal sorting complex required for transport (ESCRT), which participates in various membrane fusion/fission events, mediates the second step. Intriguingly, in archaea, ESCRT is involved in cytokinesis, raising the hypothesis that the function of ESCRT in eukaryotic cytokinesis descended from the archaeal ancestor.

aurora kinase phosphorylates evolutionarily conserved sites on its target to regulate mitochondrial division.

The mitochondrion is an organelle that was derived from an endosymbiosis. Although regulation of mitochondrial growth by the host cell is necessary for the maintenance of mitochondria, it is unclear how this regulatory mechanism was acquired. To address this, we studied the primitive unicellular red alga , which has the simplest eukaryotic genome and a single mitochondrion.

Dynamics of the nucleoside diphosphate kinase protein DYNAMO2 correlates with the changes in the global GTP level during the cell cycle of Cyanidioschyzon merolae.

GTP is an essential source of energy that supports a large array of cellular mechanochemical structures ranging from protein synthesis machinery to cytoskeletal apparatus for maintaining the cell cycle. However, GTP regulation during the cell cycle has been difficult to investigate because of heterogenous levels of GTP in asynchronous cell cycles and genetic redundancy of the GTP-generating enzymes. Here, in the unicellular red algae Cyanidioschyzon merolae, we demonstrated that the ATP-GTP-converting enzyme DYNAMO2 is an essential regulator of global GTP levels during the cell cycle.

The sole LSm complex in associates with pre-mRNA splicing and mRNA degradation factors.

Proteins of the Sm and Sm-like (LSm) families, referred to collectively as (L)Sm proteins, are found in all three domains of life and are known to promote a variety of RNA processes such as base-pair formation, unwinding, RNA degradation, and RNA stabilization. In eukaryotes, (L)Sm proteins have been studied, inter alia, for their role in pre-mRNA splicing. In many organisms, the LSm proteins form two distinct complexes, one consisting of LSm1-7 that is involved in mRNA degradation in the cytoplasm, and the other consisting of LSm2-8 that binds spliceosomal U6 snRNA in the nucleus.

Surfing the vegetal pole in a small population: extracellular vertical transmission of an 'intracellular' deep-sea clam symbiont.

Symbiont transmission is a key event for understanding the processes underlying symbiotic associations and their evolution. However, our understanding of the mechanisms of symbiont transmission remains still fragmentary. The deep-sea clam Calyptogena okutanii harbours obligate sulfur-oxidizing intracellular symbiotic bacteria in the gill epithelial cells.

Identification of highly-disrupted tRNA genes in nuclear genome of the red alga, Cyanidioschyzon merolae 10D.

The limited locations of tRNA introns are crucial for eukaryal tRNA-splicing endonuclease recognition. However, our analysis of the nuclear genome of an early-diverged red alga, Cyanidioschyzon merolae, demonstrated the first evidence of nuclear-encoded tRNA genes that contain ectopic and/or multiple introns. Some genes exhibited both intronic and permuted structures in which the 3'-half of the tRNA coding sequence lies upstream of the 5'-half, and an intron is inserted into either half.

Single-membrane-bounded peroxisome division revealed by isolation of dynamin-based machinery.

Peroxisomes (microbodies) are ubiquitous single-membrane-bounded organelles and fulfill essential roles in the cellular metabolism. They are found in virtually all eukaryotic cells and basically multiply by division. However, the mechanochemical machinery involved in peroxisome division remains elusive.

The kinesin-like protein TOP promotes Aurora localisation and induces mitochondrial, chloroplast and nuclear division.

The cell cycle usually refers to the mitotic cycle, but the cell-division cycle in the plant kingdom consists of not only nuclear but also mitochondrial and chloroplast division cycle. However, an integrated control system that initiates division of the three organelles has not been found. We report that a novel C-terminal kinesin-like protein, three-organelle division-inducing protein (TOP), controls nuclear, mitochondrial and chloroplast divisions in the red alga Cyanidioschyzon merolae.

Golgi inheritance in the primitive red alga, Cyanidioschyzon merolae.

The Golgi body has important roles in modifying, sorting, and transport of proteins and lipids. Eukaryotic cells have evolved in various ways to inherit the Golgi body from mother to daughter cells, which allows the cells to function properly immediately after mitosis. Here we used Cyanidioschyzon merolae, one of the most suitable systems for studies of organelle dynamics, to investigate the inheritance of the Golgi.

The plastid-dividing machinery: formation, constriction and fission.

Plastids divide by constriction of the plastid-dividing (PD) machinery, which encircles the division site. The PD machinery consists of the stromal inner machinery which includes the inner PD and filamenting temperature-sensitive mutant Z (FtsZ) rings and the cytosolic outer machinery which includes the outer PD and dynamin rings. The major constituent of the PD machinery is the outer PD ring, which consists of a bundle of polyglucan filaments.

The soybean F3'H protein is localized to the tonoplast in the seed coat hilum.

We previously isolated a soybean (Glycine max (L.) Merr.) flavonoid 3'-hydroxylase (F3'H) gene (sf3'h1) corresponding to the T locus, which controls pubescence and seed coat color, from two near-isogenic lines (NILs), To7B (TT) and To7G (tt).

Mitotic inheritance of endoplasmic reticulum in the primitive red alga Cyanidioschyzon merolae.

Endoplasmic reticulum (ER) is a major site for secretory protein folding and lipid synthesis. Since ER cannot be synthesized de novo, it must be inherited during the cell cycle. Studying ER inheritance can however be difficult because the ER of typical plant and animal cells is morphologically complex.

The cell cycle, including the mitotic cycle and organelle division cycles, as revealed by cytological observations.

It is generally believed that the cell cycle consists essentially of the mitotic cycle, which involves mitosis and cytokinesis. These processes are becoming increasingly well understood at the molecular level. However, successful cell reproduction requires duplication and segregation (inheritance) of all of the cellular contents, including not only the cell-nuclear genome but also intracellular organelles.

Chloroplasts divide by contraction of a bundle of nanofilaments consisting of polyglucan.

In chloroplast division, the plastid-dividing (PD) ring is a main structure of the PD machinery and is a universal structure in the plant kingdom. However, the components and formation of the PD ring have been enigmatic. By proteomic analysis of PD machineries isolated from Cyanidioschyzon merolae, we identified the glycosyltransferase protein plastid-dividing ring 1 (PDR1), which constructs the PD ring and is widely conserved from red alga to land plants.

The coiled-coil protein VIG1 is essential for tethering vacuoles to mitochondria during vacuole inheritance of Cyanidioschyzon merolae.

Vacuoles/lysosomes function in endocytosis and in storage and digestion of metabolites. These organelles are inherited by the daughter cells in eukaryotes. However, the mechanisms of this inheritance are poorly understood because the cells contain multiple vacuoles that behave randomly.