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PubMed2000

The plastid ribosomal proteins. Identification of all the proteins in the 50 S subunit of an organelle ribosome (chloroplast).

We have completed identification of all the ribosomal proteins (RPs) in spinach plastid (chloroplast) ribosomal 50 S subunit via a proteomic approach using two-dimensional electrophoresis, electroblotting/protein sequencing, high performance liquid chromatography purification, polymerase chain reaction-based screening of cDNA library/nucleotide sequencing, and mass spectrometry (reversed-phase HPLC coupled to electrospray ionization mass spectrometry and electrospray ionization mass spectrometry). Spinach plastid 50 S subunit comprises 33 proteins, of which 31 are orthologues of Escherichia coli RPs and two are plastid-specific RPs (PSRP-5 and PSRP-6) having no homologues in other types of ribosomes. Orthologues of E. coli L25 and L30 are absent in spinach plastid ribosome. 25 of the plastid 50 S RPs are encoded in the nuclear genome and synthesized on cytosolic ribosomes, whereas eight of the plastid RPs are encoded in the plastid organelle genome and synthesized on plastid ribosomes. Sites for transit peptide cleavages in the cytosolic RP precursors and formyl Met processing in the plastid-synthesized RPs were established. Post-translational modifications were observed in several mature plastid RPs, including multiple forms of L10, L18, L31, and PSRP-5 and N-terminal/internal modifications in L2, L11 and L16. Comparison of the RPs in gradient-purified 70 S ribosome with those in the 30 and 50 S subunits revealed an additional protein, in approximately stoichiometric amount, specific to the 70 S ribosome. It was identified to be plastid ribosome recycling factor. Combining with our recent study of the proteins in plastid 30 S subunit (Yamaguchi, K., von Knoblauch, K., and Subramanian, A. R. (2000) J. Biol. Chem. 275, 28455-28465), we show that spinach plastid ribosome comprises 59 proteins (33 in 50 S subunit and 25 in 30 S subunit and ribosome recycling factor in 70 S), of which 53 are E. coli orthologues and 6 are plastid-specific proteins (PSRP-1 to PSRP-6). We propose the hypothesis that PSRPs were evolved to perform functions unique to plastid translation and its regulation, including protein targeting/translocation to thylakoid membrane via plastid 50 S subunit.

Amino Acid Sequence↗
PubMed2006

Rate variation as a function of gene origin in plastid-derived genes of peridinin-containing dinoflagellates.

Peridinin-pigmented dinoflagellates contain secondary plastids that seem to have undergone more nearly complete plastid genome reduction than other eukaryotes. Many typically plastid-encoded genes appear to have been transferred to the nucleus, with a few remaining genes found on minicircles. To understand better the evolution of the dinoflagellate plastid, four categories of plastid-associated genes in dinoflagellates were defined based on their history of transfer and evaluated for rate of sequence evolution, including minicircle genes (presumably plastid-encoded), genes probably transferred from the plastid to the nucleus (plastid-transferred), and genes that were likely acquired directly from the nucleus of the previous plastid host (nuclear-transferred). The fourth category, lateral-transferred genes, are plastid-associated genes that do not appear to have a cyanobacterial origin. The evolutionary rates of these gene categories were compared using relative rate tests and likelihood ratio tests. For comparison with other secondary plastid-containing organisms, rates were calculated for the homologous sequences from the haptophyte Emiliania huxleyi. The evolutionary rate of minicircle and plastid-transferred genes in the dinoflagellate was strikingly higher than that of nuclear-transferred and lateral-transferred genes and, also, substantially higher than that of all plastid-associated genes in the haptophyte. Plastid-transferred genes in the dinoflagellate had an accelerated rate of evolution that was variable but, in most cases, not as extreme as the minicircle genes. Furthermore, the nuclear-transferred and lateral-transferred genes showed rates of evolution that are similar to those of other taxa. Thus, nucleus-to-nucleus transferred genes have a more typical rate of sequence evolution, while those whose history was wholly or partially within the dinoflagellate plastid genome have a markedly accelerated rate of evolution.

Animals↗
PubMed2003

Plastid division: its origins and evolution.

Photosynthetic eukaryotes have evolved plastid division mechanisms since acquisition of plastids through endosymbiosis. The emerging evolutionary origin of the plastid division mechanism is remarkably complex. The constituents of the division apparatus of plastids may have complex origins. The one constituent is the plastid FtsZ ring taken over from the cyanobacteria-like ancestral endosymbionts. The second is the doublet of concentric plastid dividing rings (or triplet in red algae), possibly acquired by ancestral host eukaryotes following the primary endosymbiotic event. Placement of the division apparatus at the correct division site may involve a system analogous to the bacterial Min system. Plastid nucleoid partitioning may be mediated by binding to envelope or thylakoid membranes. Multiple copies of plastid DNA and symmetrical distribution of the nucleoids in the plastids may permit faithful transmission to daughter plastids via equal binary plastid divisions. Cyanelles retain peptidoglycan wall and cyanelle division occurs through septum formation such as bacterial cell division. Cyanelle division involves the cyanelle ring analogous to the inner stromal plastid-dividing (PD) ring. According to the prevailing hypothesis that primary endosymbiosis occurred only once, cyanelle division may represent an intermediate stage between cyanobacterial division and the well-known plastid division among extant plants. With the secondary plastids, which are surrounded by three or four membranes, the PD ring also participates in division of the inner two "true" plastid envelope membranes, and the third and the outermost membranes divide by unknown mechanisms.

Animals↗
PubMed2006

A tertiary plastid uses genes from two endosymbionts.

The origin and subsequent spread of plastids by endosymbiosis had a major environmental impact and altered the course of a great proportion of eukaryotic biodiversity. The ancestor of dinoflagellates contained a secondary plastid that was acquired in an ancient endosymbiotic event, where a eukaryotic cell engulfed a red alga. This is known as secondary endosymbiosis and has happened several times in eukaryotic evolution. Certain dinoflagellates, however, are unique in having replaced this secondary plastid in an additional (tertiary) round of endosymbiosis. Most plastid proteins are encoded in the nucleus of the host and are targeted to the organelle. When secondary or tertiary endosymbiosis takes place, it is thought that these genes move from nucleus to nucleus, so the plastid retains the same proteome. We have conducted large-scale expressed sequence tag (EST) surveys from Karlodinium micrum, a dinoflagellate with a tertiary haptophyte-derived plastid, and two haptophytes, Isochrysis galbana and Pavlova lutheri. We have identified all plastid-targeted proteins, analysed the phylogenetic origin of each protein, and compared their plastid-targeting transit peptides. Many plastid-targeted genes in the Karlodinium nucleus are indeed of haptophyte origin, but some genes were also retained from the original plastid (showing the two plastids likely co-existed in the same cell), in other cases multiple isoforms of different origins exist. We analysed plastid-targeting sequences and found the transit peptides in K.micrum are different from those found in either dinoflagellates or haptophytes, pointing to a plastid with an evolutionarily chimeric proteome, and a massive remodelling of protein trafficking during plastid replacement.

Algal Proteins↗
PubMed2005

The tobacco plastid accD gene is essential and is required for leaf development.

Angiosperm plastid genomes typically encode approximately 80 polypeptides, mainly specifying plastid-localized functions such as photosynthesis and gene expression. Plastid protein synthesis and expression of the plastid clpP1 gene are essential for development in tobacco, indicating the presence of one or more plastid genes whose influence extends beyond the plastid compartment. The plastid accD gene encodes the beta-carboxyl transferase subunit of acetyl-CoA carboxylase and is present in the plastids of most flowering plants, including non-photosynthetic parasitic plants. We replaced the wild-type accD gene with an aadA-disrupted mutant allele using homologous recombination. Persistent heteroplasmy in the presence of antibiotics indicated that the wild-type accD allele was essential. The phenotype of the accD knockout was revealed in plastid transformants grown in the absence of antibiotics. Leaves contained pale green sectors and lacked part or all of the leaf lamina due to arrested division or loss of cells. Abnormal structures were present in plastids found in mutant plants, indicating that accD might be required to maintain the plastid compartment. Loss of the plastid compartment would be expected to be lethal. These results provide genetic evidence showing the essential role of plastid ACCase in the pathway leading to the synthesis of products required for the extra-plastidic processes needed for leaf development.

Genes, Essential↗
PubMed2006

Plastid biogenesis, between light and shadows.

Plastids are cellular organelles which originated when a photosynthetic prokaryote was engulfed by the eukaryotic ancestor of green and red algae and land plants. Plastids have diversified in plants from their original function as chloroplasts to fulfil a variety of other roles in metabolite biosynthesis and in storage, or purely to facilitate their own transmission, according to the cell type that harbours them. Therefore cellular development and plastid biogenesis pathways must be closely intertwined. Cell biological, biochemical, and genetic approaches have generated a large body of knowledge on a variety of plastid biogenesis processes. A brief overview of the components and functions of the plastid genetic machinery, the plastid division apparatus, and protein import to and targeting inside the organelle is presented here. However, key areas in which our knowledge is still surprisingly limited remain, and these are also discussed. Chloroplast-defective mutants suggest that a substantial number of important plastid biogenesis proteins are still unknown. Very little is known about how different plastid types differentiate, or about what mechanisms co-ordinate cell growth with plastid growth and division, in order to achieve what is, in photosynthetic cells, a largely constant cellular plastid complement. Further, it seems likely that major, separate plastid and chloroplast 'master switches' exist, as indicated by the co-ordinated gene expression of plastid or chloroplast-specific proteins. Recent insights into each of these developing areas are reviewed. Ultimately, this information should allow us to gain a systems-level understanding of the plastid-related elements of the networks of plant cellular development.

Biological Evolution↗
PubMed2000

Plastid tubules of higher plants are tissue-specific and developmentally regulated.

Green fluorescent stroma filled tubules (stromules) emanating from the plastid surface were observed in transgenic plants containing plastid-localized green fluorescent protein (GFP). These transgenic tobacco plants were further investigated by epifluorescence and confocal laser scanning microscopy (CSLM) to identify developmental and/or cell type specific differences in the abundance and appearance of stromules and of plastids. Stromules are rarely seen on chlorophyll-containing plastids in cell types such as trichomes, guard cells or mesophyll cells of leaves. In contrast, they are abundant in tissues that contain chlorophyll-free plastids, such as petal and root. The morphology of plastids in roots and petals is highly dynamic, and plastids are often elongated and irregular. The shapes, size, and position of plastids vary in particular developmental zones of the root. Furthermore, suspension cells of tobacco exhibit stromules on virtually every plastid with two major forms of appearance. The majority of cells show a novel striking 'octopus- or millipede-like' structure with plastid bodies clustered around the nucleus and with long thin stromules of up to at least 40 (micro)m length stretching into distant areas of the cell. The remaining cells have plastid bodies distributed throughout the cell with short stromules. Photobleaching experiments indicated that GFP can flow through stromules and that the technique can be used to distinguish interconnected plastids from independent plastids.

Cell Differentiation↗
PubMed2001

Plastid division is driven by a complex mechanism that involves differential transition of the bacterial and eukaryotic division rings.

During plastid division, two structures have been detected at the division site in separate analyses. The plastid-dividing ring can be detected by transmission electron microscopy as two (or three) electron-dense rings: an outer ring on the cytosolic face of the outer envelope, occasionally a middle ring in the intermembrane space, and an inner ring on the stromal face of the inner envelope. The FtsZ ring, which plays a central role in bacterial division, also is involved in plastid division and is believed to have descended to plastids from cyanobacterial endosymbiosis. The relationship between the two structures is not known, although there is discussion regarding whether they are identical. Biochemical and immunocytochemical investigations, using synchronized chloroplasts of the red alga Cyanidioschyzon merolae, showed that the plastid FtsZ ring is distinct and separable from the plastid-dividing ring. The FtsZ ring localizes in stroma and faces the inner plastid-dividing ring at the far side from the inner envelope. The FtsZ ring and the inner and outer plastid-dividing rings form in that order before plastid division. The FtsZ ring disappears at the late stage of constriction before dissociation of the plastid-dividing ring, when the constriction is still in progress. Our results suggest that the FtsZ ring;-based system, which originated from a plastid ancestor, cyanobacteria, and the plastid-dividing ring;-based system, which probably originated from host eukaryotic cells, form a complex and are involved in plastid division by distinct modes.

Arabidopsis Proteins↗
PubMed2001

Multiple pathways for Cre/lox-mediated recombination in plastids.

Plastid transformation technology involves the insertion by homologous recombination and subsequent amplification of plastid transgenes to approximately 10 000 genome copies per leaf cell. Selection of transformed genomes is achieved using a selectable antibiotic resistance marker that has no subsequent role in the transformed line. We report here a feasibility study in the model plant tobacco, to test the heterologous Cre/lox recombination system for antibiotic marker gene removal from plastids. To study its efficiency, a green fluorescent protein reporter gene activation assay was utilized that allowed visual observation of marker excision after delivery of Cre to plastids. Using a combination of in vivo fluorescence activation and molecular assays, we show that transgene excision occurs completely from all plastid genomes early in plant development. Selectable marker-free transplastomic plants are obtained in the first seed generation, indicating a potential application of the Cre/lox system in plastid transformation technology. In addition to the predicted transgene excision event, two alternative pathways of Cre-mediated recombination were also observed. In one alternative pathway, the presence of Cre in plastids stimulated homologous recombination between a 117 bp transgene expression element and its cognate sequence in the plastid genome. The other alternative pathway uncovered a plastid genome 'hot spot' of recombination composed of multiple direct repeats of a 5 bp sequence motif, which recombined with lox independent of sequence homology. Both recombination pathways result in plastid genome deletions. However, the resultant plastid mutations are silent, and their study provides the first insights into tRNA accumulation and trans-splicing events in higher plant plastids.

Arabidopsis↗
PubMed2002

Molecular evidence for plastid robbery (Kleptoplastidy) in Dinophysis, a dinoflagellate causing diarrhetic shellfish poisoning.

The dinoflagellate genus Dinophysis contains species known to cause diarrhetic shellfish poisoning. Although most photosynthetic dinoflagellates have plastids with peridinin, photosynthetic Dinophysis species have cryptophyte-like plastids containing phycobilin rather than peridinin. We sequenced nuclear- and plastid-encoded SSU rDNA from three photosynthetic species of Dinophysis for phylogenetic analyses. In the tree of nuclear SSU rDNA, Dinophysis was a monophyletic group nested with peridinin-containing dinoflagellates. However, in the tree of plastid SSU rDNA, the Dinophysis plastid lineage was within the radiation of cryptophytes and was closely related to Geminigera cryophila. These analyses indicate that an ancestor of Dinophysis, which may have originally possessed peridinin-type plastid and lost it subsequently, adopted a new plastid from a cryptophyte. Unlike dinoflagellates with fully integrated plastids, the Dinophysis plastid SSU rDNA sequences were identical among the three species examined, while there were species-specific base substitutions in their nuclear SSU rDNA sequences. Queries of the DNA database showed that the plastid SSU rDNA sequence of Dinophysis is almost identical to that of an environmental DNA clone of a <10 pm sized plankter, possibly a cryptophyte and a likely source of the Dinophysis plastid. The present findings suggest that these Dinophysis species engulfed and temporarily retained plastids from a cryptophyte.

Animals↗
PubMed2005

The molecular biology of plastid division in higher plants.

Plastids are essential plant organelles vital for life on earth, responsible not only for photosynthesis but for many fundamental intermediary metabolic reactions. Plastids are not formed de novo but arise by binary fission from pre-existing plastids, and plastid division therefore represents an important process for the maintenance of appropriate plastid populations in plant cells. Plastid division comprises an elaborate pathway of co-ordinated events which include division machinery assembly at the division site, the constriction of envelope membranes, membrane fusion and, ultimately, the separation of the two new organelles. Because of their prokaryotic origin bacterial cell division has been successfully used as a paradigm for plastid division. This has resulted in the identification of the key plastid division components FtsZ, MinD, and MinE, as well as novel proteins with similarities to prokaryotic cell division proteins. Through a combination of approaches involving molecular genetics, cell biology, and biochemistry, it is now becoming clear that these proteins act in concert during plastid division, exhibiting both similarities and differences compared with their bacterial counterparts. Recent efforts in the cloning of the disrupted loci in several of the accumulation and replication of chloroplasts mutants has further revealed that the division of plastids is controlled by a combination of prokaryote-derived and host eukaryote-derived proteins residing not only in the plastid stroma but also in the cytoplasm. Based on the available data to date, a working model is presented showing the protein components involved in plastid division, their subcellular localization, and their protein interaction properties.

Cell Division↗
PubMed2005

Identification and characterization of a new conserved motif within the presequence of proteins targeted into complex diatom plastids.

Several groups of algae evolved by secondary endocytobiosis, which is defined as the uptake of a eukaryotic alga into a eukaryotic host cell and the subsequent transformation of the endosymbiont into an organelle. Due to this explicit evolutionary history such algae possess plastids that are surrounded by either three or four membranes. Protein targeting into plastids of these organisms depends on N-terminal bipartite presequences consisting of a signal and a transit peptide domain. This suggests that different protein targeting systems may have been combined during establishment of secondary endocytobiosis to enable the transport of proteins into the plastids. Here we demonstrate the presence of an apparently new type of transport into diatom plastids. We analyzed protein targeting into the plastids of diatoms and identified a conserved amino acid sequence motif within plastid preprotein targeting sequences. We expressed several diatom plastid presequence:GFP fusion proteins with or without modifications within that motif in the diatom Phaeodactylum tricornutum and found that a single conserved phenylalanine is crucial for protein transport into the diatom plastids in vivo, thus indicating the presence of a so far unknown new type of targeting signal. We also provide experimental data about the minimal requirements of a diatom plastid targeting presequence and demonstrate that the signal peptides of plastid preproteins and of endoplasmic reticulum-targeted preproteins in diatoms are functionally equivalent. Furthermore we show that treatment of the cells with Brefeldin A arrests protein transport into the diatom plastids suggesting that a vesicular transport step within the plastid membranes may occur.

Algal Proteins↗
PubMed1993

Chloroplast rps15 and the rpoB/C1/C2 gene cluster are strongly transcribed in ribosome-deficient plastids: evidence for a functioning non-chloroplast-encoded RNA polymerase.

Transcription of plastid genes and transcript accumulation were investigated in white leaves of the albostrians mutant of barley (Hordeum vulgare) and in heat-bleached leaves of rye (Secale cereale) as well as in normal green leaves of both species. Cells of white leaves of the mutant and cells of heat-bleached leaves bear undifferentiated plastids lacking ribosomes and, consequently, plastid translation products, among them the subunits of a putative chloroplast RNA polymerase encoded by the plastid genes rpoA, B, C1 and C2. The following results were obtained. (i) Plastid genes are transcribed despite the lack of chloroplast gene-encoded RNA polymerase subunits. The plastid origin of these transcripts was proven. This finding provides evidence for the existence of a plastid RNA polymerase encoded entirely by nuclear genes. (ii) Transcripts of the rpo genes and of rps15, but not of genes involved in photosynthesis and related processes (psbA, rbcL, atpI-H), were abundantly accumulated in ribosome-deficient plastids. In contrast, chloroplasts accumulated transcripts of photosynthetic, but not of the rpo genes. (iii) Differences in transcript accumulation between chloroplasts and ribosome-deficient plastids are due to different relative transcription rates and different transcript stability. (iv) The observed differences in transcription are not caused by an altered pattern of methylation of plastid DNA. Thus, the prokaryotic plastid genome of higher plants is transcribed by two RNA polymerases. The observed differences in transcription between chloroplasts and undifferentiated plastids might reflect different functions of the two enzymes.

Chloroplasts↗
PubMed2004

Stable transformation of petunia plastids.

Plastid transformation results in stably expressed foreign genes, which for most Angiosperms are largely excluded from sperm cells, thereby greatly reducing the risk of foreign gene spread through pollen. Prior to this work, fertile plastid transformants were restricted to tobacco, tomato and Lesquerella. Application of plastid engineering in the important floriculture industry requires the development of stable plastid transformation in a major ornamental plant species such as Petunia hybrida. Here we describe the successful isolation of fertile and stable plastid transformants in a commercial cultivar of P. hybrida (var. Pink Wave). Plastid targeting regions from tobacco were used to integrate aadA and gusA between the accD and rbcL genes of P. hybrida plastid DNA following particle bombardment of leaves. For three spectinomycin and streptomycin resistant lines, DNA blot analysis confirmed transgene integration into plastid DNA and homoplasmy. Maternal inheritance and homoplasmy resulted in 100% transmission of spectinomycin resistance to progeny after selfing. Plastid transformants expressed the gusA gene uniformly within leaves and to comparable levels in all three lines. Insertion of trait genes in place of gusA coding sequences enables immediate applications of our plastid transformation vector. Establishment of plastid transformation in P. hybrida facilitates a safe and reliable use of this important ornamental plant for research and plant biotechnology.

Drug Resistance↗
PubMed1996

The growing importance of the plastid-like DNAs of the Apicomplexa.

Organisms in the phylum Apicomplexa possess, in addition to their mitochondrial genome, an extrachromosomal DNA that possesses significant similarities with the extrachromosomal genomes of plastids. To date, the majority of data on these plastid-like DNAs have been obtained from the human malarial organism, Plasmodium falciparum. In common with plastid DNAs, the plastid-like DNA of P. falciparum possesses genes for DNA-dependent RNA polymerase subunits beta and beta 1 and for organellar-like large- and small-subunits ribosomal RNAs. Both the polymerase subunit and ribosomal RNA gene sequences share a number of features with those from plastid DNAs. In addition, the ribosomal RNA genes are organised in an inverted repeat arrangement, reminiscent of plastid DNAs. Additional molecular features shared between the 2 genomes are discussed. Plastid-like DNAs have also been identified in other Plasmodium species as well as Toxoplasma gondii, Eimeria tenella, Babesia bovis and a number of Sarcocystis species. A cryptic organelle often observed in apicomplexans has been proposed as the organelle that harbours the plastid-like DNAs, but conclusive evidence for this has not yet been obtained. Although approximately 1/2 of the plastid-like DNA of P. falciparum has been sequenced to date, no function has yet been ascribed to this DNA or its putative organelle. Phylogenetic inferences based on sequence data from this DNA have indicated an evolutionary origin from photosynthetic organisms, but the true provenance of the plastid-like DNAs remains to be determined. Because of the specific nature of the plastid-like DNAs, they may prove useful as effective targets for chemotherapeutics.

Animals↗
PubMed1999

Homeologous plastid DNA transformation in tobacco is mediated by multiple recombination events.

Efficient plastid transformation has been achieved in Nicotiana tabacum using cloned plastid DNA of Solanum nigrum carrying mutations conferring spectinomycin and streptomycin resistance. The use of the incompletely homologous (homeologous) Solanum plastid DNA as donor resulted in a Nicotiana plastid transformation frequency comparable with that of other experiments where completely homologous plastid DNA was introduced. Physical mapping and nucleotide sequence analysis of the targeted plastid DNA region in the transformants demonstrated efficient site-specific integration of the 7.8-kb Solanum plastid DNA and the exclusion of the vector DNA. The integration of the cloned Solanum plastid DNA into the Nicotiana plastid genome involved multiple recombination events as revealed by the presence of discontinuous tracts of Solanum-specific sequences that were interspersed between Nicotiana-specific markers. Marked position effects resulted in very frequent cointegration of the nonselected peripheral donor markers located adjacent to the vector DNA. Data presented here on the efficiency and features of homeologous plastid DNA recombination are consistent with the existence of an active RecA-mediated, but a diminished mismatch, recombination/repair system in higher-plant plastids.

Base Sequence↗
PubMed2005

Chlorophyll c-containing plastid relationships based on analyses of a multigene data set with all four chromalveolate lineages.

The chlorophyll c-containing algae comprise four major lineages: dinoflagellates, haptophytes, heterokonts, and cryptophytes. These four lineages have sometimes been grouped together based on their pigmentation, but cytological and rRNA data had suggested that they were not a monophyletic lineage. Some molecular data support monophyly of the plastids, while other plastid and host data suggest different relationships. It is uncontroversial that these groups have all acquired plastids from another eukaryote, probably from the red algal lineage, in a secondary endosymbiotic event, but the number and sequence of such event(s) remain controversial. Understanding chlorophyll c-containing plastid relationships is a first step towards determining the number of endosymbiotic events within the chromalveolates. We report here phylogenetic analyses using 10 plastid genes with representatives of all four chromalveolate lineages. This is the first organellar genome-scale analysis to include both haptophytes and dinoflagellates. Concatenated analyses support the monophyly of the chlorophyll c-containing plastids and suggest that cryptophyte plastids are the basal member of the chlorophyll c-containing plastid lineage. The gene psbA, which has at times been used for phylogenetic purposes, was found to differ from the other genes in its placement of the dinoflagellates and the haptophytes, and in its lack of support for monophyly of the green and red plastid lineages. Overall, the concatenated data are consistent with a single origin of chlorophyll c-containing plastids from red algae. However, these data cannot test several key hypothesis concerning chromalveolate host monophyly, and do not preclude the possibility of serial transfer of chlorophyll c-containing plastids among distantly related hosts.

Amino Acid Sequence↗
PubMed2004

Heterogeneous pollen in Chlorophytum comosum, a species with a unique mode of plastid inheritance intermediate between the maternal and biparental modes.

The majority of angiosperms display maternal plastid inheritance. The cytological mechanisms of this mode of inheritance have been well studied, but little is known about its genetic relationship to biparental inheritance. The angiosperm Chlorophytum comosum is unusual in that different pollen grains show traits of different modes of plastid inheritance. About 50% of these pollen grains exhibit the potential for biparental plastid inheritance, whereas the rest exhibit maternal plastid inheritance. There is no morphological difference between these two types of pollen. Pollen grains from different individuals of C. comosum all exhibited this variability. Closer examination revealed that plastid polarization occurs, with plastids being excluded from the generative cell during the first pollen mitosis. However, the exclusion is incomplete in 50% of the pollen grains, and the few plastids distributed to the generative cells divide actively after mitosis. Immunoelectron microscopy using an anti-DNA antibody demonstrated that the plastids contain a large amount of DNA. As there is a considerable discrepancy between the exclusion and duplication of plastids, resulting in plastids with opposite fates occurring simultaneously in C. comosum, we propose that the species is a transitional type with a mode of plastid inheritance that is genetically intermediate between the maternal and biparental modes.

Asparagaceae↗