Two atypical ANGUSTIFOLIA without a plant-specific C-terminus regulate gametophore and sporophyte shapes in the moss Physcomitrium (Physcomitrella) patens

ANGUSTIFOLIA (AN) is a plant-specific subfamily of the CtBP/BARS/AN family, characterized by a plant-specific C-terminal domain of approximately 200 amino acids. Previously, we revealed that double knockout (DKO) lines of Physcomitrium (Physcomitrella) patens ANGUSTIFOLIA genes (PpAN1-1 and PpAN1-2) show defects in gametophore height and the lengths of the seta and foot region of sporophytes, by reduced cell elongation. In addition to two canonical ANs, the genome of P. patens has two atypical ANs without a coding region for a plant-specific C-terminus (PpAN2-1 and PpAN2-2); these were investigated in this study. Similar to PpAN1s, both promoters of the PpAN2 genes were highly active in the stems of haploid gametophores and in the middle-to-basal region of young diploid sporophytes that develop into the seta and foot. Analyses of PpAN2-1/2-2 DKO and PpAN quadruple knockout (QKO) lines implied that these four AN genes have partially redundant functions to regulate cell elongation in their expression regions. Transgenic strains harboring P. patens α-tubulin fused to green fluorescent protein, which were generated from a QKO line, showed that the orientation of the microtubules in the gametophore tips in the PpAN QKO lines was unchanged from the wild-type and PpAN1-1/1-2 DKO plants. In addition to both PpAN2-1 and PpAN2-2, short Arabidopsis AN without the C-terminus of 200 amino acids could rescue the Arabidopsis thaliana an-1 phenotypes, implying AN activity is dependent on the N-terminal regions.

Two ANGUSTIFOLIA genes regulate gametophore and sporophyte development in Physcomitrella patens

In Arabidopsis thaliana the ANGUSTIFOLIA (AN) gene regulates the width of leaves by controlling the diffuse growth of leaf cells in the medio-lateral direction. In the genome of the moss Physcomitrella patens, we found two normal ANs (PpAN1-1 and 1-2). Both PpAN1 genes complemented the A. thaliana an-1 mutant phenotypes. An analysis of spatiotemporal promoter activity of each PpAN1 gene, using transgenic lines that contained each PpAN1-promoter- uidA (GUS) gene, showed that both promoters are mainly active in the stems of haploid gametophores and in the middle to basal region of the young sporophyte that develops into the seta and foot. Analyses of the knockout lines for PpAN1-1 and PpAN1-2 genes suggested that these genes have partially redundant functions and regulate gametophore height by controlling diffuse cell growth in gametophore stems. In addition, the seta and foot were shorter and thicker in diploid sporophytes, suggesting that cell elongation was reduced in the longitudinal direction, whereas no defects were detected in tip-growing protonemata. These results indicate that both PpAN1 genes in P. patens function in diffuse growth of the haploid and diploid generations but not in tip growth. To visualize microtubule distribution in gametophore cells of P. patens, transformed lines expressing P. patens α-tubulin fused to sGFP were generated. Contrary to expectations, the orientation of microtubules in the tips of gametophores in the PpAN1-1/1-2 double-knockout lines was unchanged. The relationships among diffuse cell growth, cortical microtubules and AN proteins are discussed.

Moss Chloroplasts Are Surrounded by a Peptidoglycan Wall Containing D-Amino Acids

It is believed that the plastids in green plants lost peptidoglycan (i.e., a bacterial cell wall-containing d-amino acids) during their evolution from an endosymbiotic cyanobacterium. Although wall-like structures could not be detected in the plastids of green plants, the moss Physcomitrella patens has the genes required to generate peptidoglycan (Mur genes), and knocking out these genes causes defects in chloroplast division. Here, we generated P patens knockout lines (∆Pp-ddl) for a homolog of the bacterial peptidoglycan-synthetic gene encoding d-Ala:d-Ala ligase. ∆Pp-ddl had a macrochloroplast phenotype, similar to other Mur knockout lines. The addition of d-Ala-d-Ala (DA-DA) to the medium suppressed the appearance of giant chloroplasts in ∆Pp-ddl, but the addition of l-Ala-l-Ala (LA-LA), DA-LA, LA-DA, or d-Ala did not. Recently, a metabolic method for labeling bacterial peptidoglycan was established using ethynyl-DA-DA (EDA-DA) and click chemistry to attach an azide-modified fluorophore to the ethynyl group. The ∆Pp-ddl line complemented with EDA-DA showed that moss chloroplasts are completely surrounded by peptidoglycan. Our findings strongly suggest that the moss plastids have a peptidoglycan wall containing d-amino acids. By contrast, no plastid phenotypes were observed in the T-DNA tagged ddl mutant lines of Arabidopsis thaliana.

Characterization of the superoxide dismutase genes of the halophyte Suaeda maritima in Japan and Egypt

Suaeda maritima varieties native to Japan and Egypt were cultured under aseptic conditions. The varieties differed in genetic distance but exhibited similar expression profiles of superoxide dismutase isozyme genes. The expression characteristics of superoxide dismutase (SOD; EC 1.15.1.1) isozyme genes from halophytic Suaeda marit ima plants native to Japan and Egypt were analyzed using young plants grown under aseptic conditions. A phylogenetic tree based on internal transcribed spacer sequences suggested that Egyptian S. maritima is related to European and India S. maritima, while Japanese S. maritima belongs to a separate clade. An in-gel SOD activity staining assay revealed that leaves from both the Egyptian and Japanese varieties showed high levels of CuZn-SOD and Fe-SOD activity, but no Mn-SOD activity; conversely, stems from both varieties showed Mn-SOD activity as well as other SOD isozyme activities. In Japanese S. maritima leaves, SOD activity was increased by incubation in growth medium containing 400 mM NaCl, while Egyptian S. maritima leaves showed elevated SOD activity in the absence of high salt. Genes encoding Mn-SOD and Fe-SOD were isolated from both plant types. RT-PCR analysis revealed that all SOD isozyme-encoding genes were expressed at the same levels in leaves from both plant types grown in normal or high-salt medium. In contrast, the expression of genes encoding choline monooxygenase and betaine aldehyde dehydrogenase, which are involved in betacyanin biosynthesis, was increased in high-salt medium. In leaves of Japanese S. maritima plants, Fe deficiency without high salt exposure preferentially decreased Fe-SOD activity. On the other hand, Fe deficiency with high salt exposure decreased not only Fe-SOD activity but also CuZn-SOD activity, suggesting that Fe availability is involved in the up-regulation of SOD isozymes mediating salt tolerance.

Preferential expression of a bromoperoxidase in sporophytes of a red alga, Pyropia yezoensis

A 2,158 bp cDNA (PyBPO1) encoding a bromoperoxidase (BPO) of 625 amino acids was isolated from Pyropia yezoensis. Phylogenetic analysis using amino acid sequences of BPOs suggested that P. yezoensis and cyanobacteria were grouped in the same clade and separated from brown algae. Genomic Southern blot analysis suggested that PyBPO1 existed as a single copy per haploid genome. RT-PCR revealed that PyBPO1 was actively expressed in filamentous sporophytes but repressed in leafy gametophytes under normal growth conditions. High expression levels of PyBPO1 in sporophytes were observed when sporophytes were grown under gametophyte conditions, suggesting that preferential expression of PyBPO1 occurs during the sporophyte phase. BPO activity of cell-free extracts from sporophytes and gametophytes was examined by activity staining on native PAGE gel using o-dianisidine. One activity band was detected in sporophyte sample, but not in gametophyte sample. In addition, we found that bromide and iodide were effective substrate, but chloride was not. BPO activity was observed-likely in chloroplasts-when sporophyte cells were incubated with o-dianisidine and hydrogen peroxide. Cellular BPO staining showed the same halogen preference identified by in-gel BPO staining. Based on GS-MS analysis, bromoform was detected in medium containing sporophytes. Bromoform was not detected under dark culture conditions but was detected in the culture exposed to low light intensity (5 μmol m(-2) s(-1)) and increased under a moderate light intensity (30 μmol m(-2) s(-1)).

Bending of protonema cells in a plastid glycolate/glycerate transporter knockout line of Physcomitrella patens

Arabidopsis LrgB (synonym PLGG1) is a plastid glycolate/glycerate transporter associated with recycling of 2-phosphoglycolate generated via the oxygenase activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO). We isolated two homologous genes (PpLrgB1 and B2) from the moss Physcomitrella patens. Phylogenetic tree analysis showed that PpLrgB1 was monophyletic with LrgB proteins of land plants, whereas PpLrgB2 was divergent from the green plant lineage. Experiments with PpLrgB–GFP fusion proteins suggested that both PpLrgB1 and B2 proteins were located in chloroplasts. We generated PpLrgB single (∆B1 and ∆B2) and double (∆B1/∆B2)-knockout lines using gene targeting of P. patens. The ∆B1 plants showed decreases in growth and photosynthetic activity, and their protonema cells were bent and accumulated glycolate. However, because ∆B2 and ∆B1/∆B2 plants showed no obvious phenotypic change relative to the wild-type or ∆B1 plants, respectively, the function of PpLrgB2 remains unclear. Arabidopsis LrgB could complement the ∆B1 phenotype, suggesting that the function of PpLrgB1 is the same as that of AtLrgB. When ∆B1 was grown under high-CO₂ conditions, all novel phenotypes were suppressed. Moreover, protonema cells of wild-type plants exhibited a bending phenotype when cultured on media containing glycolate or glycerate, suggesting that accumulation of photorespiratory metabolites caused P. patens cells to bend.

Reverse Transcriptase-Like Sequences Related to Retrotransposon in a Red Alga,Porphyra yezoensis

Four DNA fragments encoding a reverse transcriptase (RT)-like gene related to that of long terminal repeat (LTR) retrotransposons were isolated from the red alga Porphyra yezoensis by genomic PCR. Southern blot analysis suggested that one clone exists as a single copy per genome. Its full-length cDNA (PyRE2A) contained RT/RNase H-like sequences, which are most closely related to those of the Volvox LTR retrotransposon, although two stop codons were present within the RT region. We did not find any sequence related to LTR retrotransposons other than RT/RNase H in RyRE2A. These results indicate that PyRE2A is a single RT/RNase H-like gene and a defective progenitor of LTR retrotransposons.

Treatment with antibiotics that interfere with peptidoglycan biosynthesis inhibits chloroplast division in the desmid Closterium

Charophytes is a green algal group closely related to land plants. We investigated the effects of antibiotics that interfere with peptidoglycan biosynthesis on chloroplast division in the desmid Closterium peracerosum–strigosum–littorale complex. To detect cells just after division, we used colchicine, which inhibits Closterium cell elongation after division. Although normal Closterium cells had two chloroplasts before and after cell division, cells treated with ampicillin, D-cycloserine, or fosfomycin had only one chloroplast after cell division, suggesting that the cells divided without chloroplast division. The antibiotics bacitracin and vancomycin showed no obvious effect. Electron microscopic observation showed that irregular-shaped chloroplasts existed in ampicillin-treated Closterium cells. Because antibiotic treatments resulted in the appearance of long cells with irregular chloroplasts and cell death, we counted cell types in the culture. The results suggested that cells with one chloroplast appeared first and then a huge chloroplast was generated that inhibited cell division, causing elongation followed by cell death.

Three dynamin-related protein 5B genes are related to plastid division in Physcomitrella patens

Dynamin family proteins in eukaryotic cells assemble into rings or spirals on the surface of membranes and pinch the membranes. We found 21 dynamin-related protein (DRP) genes in the Physcomitrella patens genome. Phylogenetic analysis indicated that three of them (PpDRP5B-1, PpDRP5B-2, and PpDRP5B-3) showed robust monophyly with Arabidopsis thaliana DRP5B and Cyanidioschyzon merolae CmDnm2, both of which are related to plastid division. Quantitative RT-PCR analysis showed that the amounts of DRP5B-3 transcripts were 14-fold and 8-fold higher than those of DRP5B-1 and DRP5B-2, respectively. We generated PpDRP5B knockout transformants for each of these genes. Subapical protonemata cells in wild-type plants had an average of 47 chloroplasts. The cells in the PpDRP5B-3 knockout transformant had slightly enlarged chloroplasts, with an average chloroplast number of 28, whereas the PpDRP5B-1 and 5B-2 knockout lines had no effect on chloroplast number in P. patens. To analyze function of each PpDRP5B gene, we generated double- and triple-knockout lines. Whereas there were 32 chloroplasts in a cell of the PpDRP5B-1/5B-2 double-knockout lines, the triple-knockout line had only a few macrochloroplasts. A transient expression assay with the triple-knockout line demonstrated that the PpDRP5B-3 gene could recover the normal chloroplast phenotype.

Isolation and characterization of the Larix gmelinii ANGUSTIFOLIA (LgAN) gene

ANGUSTIFOLIA (AN), a plant homolog of C-terminal binding protein, controls the polar elongation of leaf cells and the trichome-branching pattern in Arabidopsis thaliana. In the present study, degenerate PCR was used to isolate an ortholog of AN, referred to as LgAN, from larch (Larix gmelinii). The LgAN cDNA is predicted to encode a protein of 646 amino acids that shows striking sequence similarity to AN proteins from other plants. The predicted amino acid sequence has a conserved NAD-dependent 2-hydroxy acid dehydrogenase (D2-HDH) motif and a plant AN-specific LxCxE/D motif at its N-terminus, as well as a plant-specific long C-terminal region. The LgAN gene is a single-copy gene that is expressed in all larch tissues. Expression of the LgAN cDNA rescued the leaf width and trichome-branching pattern defects in the angustifolia-1 (an-1) mutant of Arabidopsis, showing that the LgAN gene has effects complementary to those of AN. These results suggest that the LgAN gene has the same function as the AN gene.

Two different clades of copia-like retrotransposons in the red alga, Porphyra yezoensis

A copia-like retrotransposon referred to as PyRE1G1 was isolated from the genome of the red alga Porphyra yezoensis. PyRE1G1 is 4807 bp in length, with 204 bp long terminal repeats (LTRs) at both ends. PyRE1G1 has an open reading frame of 1401 residues encoding gag, protease, integrase, reverse transcriptase (RT), and RNase H. From the order of gene arrangement of proteins, PyRE1G1 appears to be a copia-like retrotransposon. Genomic Southern blot analysis suggests that PyRE1G1 consists of a small gene family. From the phylogenetic tree of RT sequences, PyRE1G1 is grouped in the clade of usual copia elements and distinct from the previously isolated red algal copia-like gene PyRE10G in that the latter is closely related to a new clade of aquatic animal-specific copia-like retrotransposons.

An Arabidopsis homolog of the bacterial peptidoglycan synthesis enzyme MurE has an essential role in chloroplast development

Enzymes encoded by bacterial MurE genes catalyze the ATP-dependent formation of uridine diphosphate-N-acetylmuramic acid-tripeptide in bacterial peptidoglycan biosynthesis. The Arabidopsis thaliana genome contains one gene with homology to the bacterial MurE:AtMurE. Under normal conditions AtMurE is expressed in leaves and flowers, but not in roots or stems. Sequence-based predictions and analyses of GFP fusions of the N terminus of AtMurE, as well as the full-length protein, suggest that AtMurE localizes to plastids. We identified three T-DNA-tagged and one Ds-tagged mutant alleles of AtMurE in A. thaliana. All four alleles show a white phenotype, and A. thaliana antisense AtMurE lines showed a pale-green phenotype. These results suggest that AtMurE is involved in chloroplast biogenesis. Cells of the mutants were inhibited in thylakoid membrane development. RT-PCR analysis of the mutant lines suggested that the expression of genes that depend on a multisubunit plastid-encoded RNA polymerase was decreased. To analyze the functional relationships between the MurE genes of cyanobacteria, the moss Physcomitrella patens and higher plants, a complementation assay was carried out with a P. patens (Pp) MurE knock-out line, which exhibits a small number of macrochloroplasts per cell. Although the Anabaena MurE, fused with the N-terminal region of PpMurE, complemented the macrochloroplast phenotype in P. patens, transformation with AtMurE did not complement this phenotype. These results suggest that AtMurE is functionally divergent from the bacterial and moss MurE proteins.

NtPolI-like1 and NtPolI-like2, bacterial DNA polymerase I homologs isolated from BY-2 cultured tobacco cells, encode DNA polymerases engaged in DNA replication in both plastids and mitochondria

Two cDNAs encoding homologs of bacterial DNA polymerase I were isolated from cultured tobacco (Nicotiana tabacum) BY-2 cells, and the corresponding genes were named NtPolI-like1 and NtPolI-like2. High sequence similarity suggested that they are orthologous genes each derived from respective parental species of N. tabacum, an allotetraploid plant. Each of the NtPolI-like1/2 gene products had a putative transit peptide for plastid localization at the N-terminus, followed by a 3'-5' exonuclease domain in the internal region, and a DNA polymerase domain in the C-terminal region. Among family A DNA polymerases, NtPolI-like proteins formed, together with other plant DNA polymerase I homologs, a phylogenetic group distinct from mitochondrial DNA polymerase gamma in animals and fungi, as well as eukaryotic cell nuclear-localized repair enzymes. In contrast to computer predictions, experiments with green fluorescent protein (GFP) fusion protein and Western blotting analysis suggested dual targeting of the gene products to both plastids and mitochondria. The recombinant NtPolI-like2 protein exhibited DNA polymerase activity in vitro. Their biochemical character roughly coincided with those of the 116 kDa DNA polymerases found in the plastid and mitochondrial nuclei (nucleoids) isolated from BY-2 cells. Pre-treatment of the organelle nuclear extracts with anti-NtPolI-like antibody removed most of the DNA polymerase activity. Reverse transcription-PCR (RT-PCR) and Western blotting analyses demonstrated transient activation of NtPolI-like gene expression in the initial phase of cell proliferation, exactly when the 116 kDa DNA polymerases in the isolated organelle nuclei were activated and preferential synthesis of organelle DNAs occurred. Taken together, our results suggest that NtPolI-like1/2 genes encode DNA polymerases engaged in DNA replication in both plastids and mitochondria.

Differential responses of antioxidative enzymes and lipid peroxidation to salt stress in salt-tolerant Plantago maritima and salt-sensitive Plantago media

The changes in plant growth, relative water content (RWC), stomatal conductance, lipid peroxidation and antioxidant system in relation to the tolerance to salt stress were investigated in salt-tolerant Plantago maritima and salt-sensitive Plantago media. The 60 days old P. maritima and P. media seedlings were subjected to 0, 100 and 200 mM NaCl for 7 days. Reduction in shoot length was higher in P. media than in P. maritima after exposure to 200 mM NaCl, but 100 mM NaCl treatment did not show any effect on shoot length of P. maritima. Shoot dry weight decreased in P. media and did not change in P. maritima. Two hundred millimolar NaCl treatment had no effect on leaf RWC in P. maritima, but it was reduced in P. media. Salt stress caused reduction in stomatal conductance being more pronounced in P. media than in P. maritima. Activities of superoxide dismutase (SOD; EC 1.15.1.1), catalase (CAT; EC 1.11.1.6), glutathione reductase (GR; EC 1.6.4.2) decreased in P. media with increasing salinity. Ascorbate peroxidase (APX; EC 1.11.1.11) activity in leaves of P. media was increased and showed no change under 100 and 200 mM NaCl, respectively. However, activities of CAT, APX and GR increased under 200 mM NaCl while their activities did not change under 100 mM NaCl in P. maritima. SOD activity in leaves of P. maritima increased with increasing salinity. Concomitant with this, four SOD activity bands were identified in leaves of P. maritima, two bands only were observed in P. media. Peroxidase (POX; EC 1.11.1.7) activity increased under both salt concentrations in P. maritima, but only under 200 mM NaCl in P. media. Confirming this, five POX activity bands were identified in leaves of P. maritima, but only two bands were determined in P. media. Malondialdehyde levels in the leaves increased under salt stress in P. media but showed no change and decreased in P. maritima at 100 and 200 mM NaCl, respectively. These results suggest that the salt-tolerant P. maritima showed a better protection mechanism against oxidative damage caused by salt stress by its higher induced activities of antioxidant enzymes than the salt-sensitive P. media.

A 100%-complete sequence reveals unusually simple genomic features in the hot-spring red alga Cyanidioschyzon merolae

BACKGROUND

All previously reported eukaryotic nuclear genome sequences have been incomplete, especially in highly repeated units and chromosomal ends. Because repetitive DNA is important for many aspects of biology, complete chromosomal structures are fundamental for understanding eukaryotic cells. Our earlier, nearly complete genome sequence of the hot-spring red alga Cyanidioschyzon merolae revealed several unique features, including just three ribosomal DNA copies, very few introns, and a small total number of genes. However, because the exact structures of certain functionally important repeated elements remained ambiguous, that sequence was not complete. Obviously, those ambiguities needed to be resolved before the unique features of the C. merolae genome could be summarized, and the ambiguities could only be resolved by completing the sequence. Therefore, we aimed to complete all previous gaps and sequence all remaining chromosomal ends, and now report the first nuclear-genome sequence for any eukaryote that is 100% complete.

RESULTS

Our present complete sequence consists of 16546747 nucleotides covering 100% of the 20 linear chromosomes from telomere to telomere, representing the simple and unique chromosomal structures of the eukaryotic cell. We have unambiguously established that the C. merolae genome contains the smallest known histone-gene cluster, a unique telomeric repeat for all chromosomal ends, and an extremely low number of transposons.

CONCLUSION

By virtue of these attributes and others that we had discovered previously, C. merolae appears to have the simplest nuclear genome of the non-symbiotic eukaryotes. These unusually simple genomic features in the 100% complete genome sequence of C. merolae are extremely useful for further studies of eukaryotic cells.

Characterization of short interspersed elements (SINEs) in a red alga, Porphyra yezoensis

Short interspersed element (SINE)-like sequences referred to as PySN1 and PySN2 were identified in a red alga, Porphyra yezoensis. Both elements contained an internal promoter with motifs (A box and B box) recognized by RNA polymerase III, and target site duplications at both ends. Genomic Southern blot analysis revealed that both elements were widely and abundantly distributed on the genome. 3' and 5' RACE suggested that PySN1 was expressed as a chimera transcript with flanking SINE-unrelated sequences and possessed the poly-A tail at the same position near the 3' end of PySN1.

Genes for the peptidoglycan synthesis pathway are essential for chloroplast division in moss

The general consensus is that a cyanobacterium phagocytosed by a host cell evolved into the plastids of red and green algae, land plants, and glaucophytes. In contrast to the plastids of glaucophytes, which retain a cyanobacterial-type peptidoglycan layer, no wall-like structures have been detected in plastids from other sources. Although the genome of Arabidopsis thaliana contains five genes that are essential for peptidoglycan synthesis, MurE, MurG, two genes for D-Ala-D-Ala ligase (Ddl), and the gene for translocase I (MraY), their functions have not been determined. We report that the moss Physcomitrella patens has nine homologous genes related to peptidoglycan biosynthesis: MurA, B, C, D, E, and F, Ddl, genes for the penicillin-binding protein Pbp, and dd-carboxypeptidase (Dac). Corroborating a computer prediction, analysis of the GFP fusion proteins with the N terminus of PpMurE or of PpPbp suggests that these proteins are located in the chloroplasts. Gene disruption of the PpMurE gene in P. patens resulted in the appearance of macrochloroplasts both in protonema and in leaf cells. Moreover, gene knockout of the P. patens Pbp gene showed inhibition of chloroplast division in this moss; however, no Pbp gene was found in A. thaliana.

Cryptic polyadenylation of transcripts of an RNA virus gene introduced into tobacco plants

We constructed an expression vector for the coat protein (CP) gene and the 3' untranslated region (3' UTR) of RNA virus (sweet potato feathery mottle virus severe strain (SPFMV-S)) lacking a foreign terminator. Out of seven transgenic tobacco plants, expression of the transgene was observed in six plants. RT-PCR analysis revealed that the transcripts had a poly(A) tail, and in most of them, polyadenylation occurred on the 5' side of the 3' UTR. These results suggest that the viral sequence contains a cryptic polyadenylation signal that permits 3'-end processing of the transcripts.

Stable genetic transformation of Larix gmelinii L. by particle bombardment of zygotic embryos

We report a new protocol for the stable transformation of Larix gmelinii. Thirty mature zygotic embryos precultured for 3 days on solid medium supplemented with benzyladenine were bombarded with plasmids pUC-GHG (GUS, HPT, and GFP genes) or pBI221-HPT (HPT and GUS genes). After a 2-month culture on selection medium, hygromycin-resistant calli appeared on the surfaces of the necrotic embryos. The frequencies of embryos with resistant calli were 18.4% and 17.4% in the transformations with pUC-GHG and pBI221-HPT DNA, respectively. More than 20 adventitious shoots formed from each of the transgenic calli. Of 17 elongated shoots selected for culturing on a rooting medium, five shoots rooted after 2 months. Expression of the GFP and GUS genes was detected in the resistant tissues by microscopic observations and by a histological GUS activity assay, respectively. PCR and Southern analysis confirmed the stable insertion of the introduced DNA into the genome.

Isolation of mutant lines with decreased numbers of chloroplasts per cell from a tagged mutant library of the moss Physcomitrella patens

Eleven mutant lines exhibiting decreased numbers of chloroplasts per cell were isolated from 8 800 tagged mutant lines of Physcomitrella patens by microscopic observations. Chloronema subapical cells in wild-type plants had a mean of 48 chloroplasts, whereas chloroplast numbers in subapical cells in mutant lines 215 and 222 decreased to 75 % of that in the wild type. Seven mutant lines - 473, 122, 221, 129, 492, 207, and 138 - had about half as many chloroplasts as the wild type. Mutant line 11 had a few remarkably enlarged chloroplasts, and mutant line 347 had chloroplasts of various sizes. Whereas the cell volume was the same as in the wild type in mutant lines 222, 473, 221, 129, 492, and 207, the cell volume of the other mutants increased. The chloroplast number of leaf cells was the same as that of chloronema cells in each mutant line when gametophores could be formed. Treatment with ampicillin decreased the number of chloroplasts in all mutant lines. Southern hybridization using DNA in tags as probes showed that only one insertion occurred in mutant lines 473 and 221. To determine whether the tagged DNA inserted into the known genes for plastid division, we isolated the PpMinD1, PpMinD2, and PpMinE1 genes. Genomic polymerase chain reaction analysis showed that the PpFtsZ and PpMinD/E genes were not disrupted by the insertion of the tags in mutant lines 11 and 347, respectively.

Efficient plant regeneration from suspension cells of Allium cepa L

Plant regeneration from calli of three cultivars of Allium cepa (Senshuki, O.Pki and Shojovaka) was investigated. Callus was induced on four variations of BDS medium containing different concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D) and 6-benzyladenine (BAP). The regeneration frequency of calli of cvs. Senshuki and O.Pki subcultured on solid MS medium supplemented with BAP ranged from 50% to 80%; this frequency decreased to less than 30% after subculture in the dark in liquid BDS medium. By repeating the dark/light transitions of the culture protocol and by selecting for green cell clusters, we were able to increase the regeneration frequency to more than 80% in all three cultivars. These cell clusters maintained a high regeneration capacity in subsequent subcultures in the absence of light for 2 months. Most (97%) of the regenerated plantlets had a normal diploid karyotype (2 n=16) that was identical to that of the mother plants, although 3% of the regenerated plants of cv. Shojovaka had a tetraploid karyotype.

Chalcone synthase-like gene in the liverwort, Marchantia paleacea var. diptera

A chalcone synthase (CHS)-like gene, MpCHSLK1, was isolated from liverwort, Marchantia paleacea var. diptera. Phylogenetic analysis revealed that MpCHSLK1 is closely related to stilbene synthase of the whisk fern, Psilotum nudum. Southern blot analysis using an MpCHSLK1 probe revealed that the gene belongs to a small gene family. Northern blot analysis indicated that CHS-like genes were expressed in either the mother plants or photoautotrophic cells. In photoautotrophic cells, the CHS-like genes were expressed light-dependently, and this expression was completely inhibited by the photosynthetic electron transport inhibitor, DCMU.

Photosynthetic Electron Transport Differentially Regulates the Expression of Superoxide Dismutase Genes in Liverwort, Marchantia paleacea var. diptera

Liverwort, Marchantia paleacea var. diptera, contains Mn-superoxide dismutase (Mn-SOD) in mitochondria, Fe-SOD in chloroplast and CuZn-SOD in cytosol. An Mn-SOD gene (MpMnSOD) was isolated from the liverwort. Using this clone together with the liverwort Fe-SOD and CuZn-SOD genes as probes, the expression of three SOD genes was investigated. Under heterotrophic conditions, the transcript of three SOD genes was accumulated light independently. On the other hand, under photoautotrophic conditions, the transcript levels of Fe-SOD and Mn-SOD increased in the light while that of CuZn-SOD decreased. The reverse occurred in the dark. In contrast to the transcript level, the activity of the three SODs was barely affected by light. The transcription inhibitor, cordycepin, inhibited either the light-promoted accumulation of Fe-SOD and Mn-SOD transcript or the light-induced reduction of the CuZn-SOD transcript. Photosynthetic electron transport inhibitors, DCMU and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone, inhibited the photo-response in three SOD genes. These results suggest that the transcript abundance of three SOD genes in liverwort is regulated by photosynthetic electron transport but the mechanism regulating the transcript abundance of the CuZn-SOD gene is different from that of the Fe-SOD and Mn-SOD genes.

Hypermethylation of retrotransposons in the liverwort Marchantia paleacea var. diptera

Three DNA fragments encoding part of a reverse transcriptase similar to that of Ty1- copia retrotransposons were isolated from suspension-cultured cells of the liverwort Marchantia paleacea var. diptera. Digestion of total DNA with methylation-sensitive and -insensitive isoschizomers revealed that, like those of the subtelomeric region, CpG sequences in retrotransposon genes were hypermethylated. The methylation status and expression of these retrotransposons was less affected by 5-azadeoxycytidine treatment compared to the subtelomeric region, which was considerably demethylated.

Copper deficiency induced expression of Fe-superoxide dismutase gene in Matteuccia struthiopteris

Iron-superoxide dismutase (Fe-SOD) activity was not detected in extracts from the leaves of ferns, Equisetum arvense and Matteuccia struthiopteris. To know why ferns lack Fe-SOD activity, the Fe-SOD like gene (MsFeSOD1) was isolated from M. struthiopteris and its expression was investigated with a focus on the metals Fe and Cu using the prothalli of the fern. The expression of MsFeSOD1 mRNA was induced by a deficiency of Cu, but Fe-SOD activity was not detected. The recombinant protein of MsFeSOD1 produced in E. coli showed Fe-SOD activity. These findings suggest that the fern Fe-SOD like gene was transcriptionally regulated by Cu but an additional mechanism is involved in the formation of an active enzyme.

Effects of antibiotics that inhibit the bacterial peptidoglycan synthesis pathway on moss chloroplast division

Moss chloroplasts should prove useful for studying the cyanobacteria-derived system in chloroplasts. To determine the effects of antibiotics that inhibit bacterial peptidoglycan synthesis, the numbers of chloroplasts in treated Physcomitrella patens cells were counted. Ampicillin and D-cycloserine caused a rapid decrease in the number of chloroplasts per cell. Fosfomycin affected half of the cells, while vancomycin affected a few cells. Conversely, bacitracin had no effect. With the decrease in chloroplast number, macrochloroplasts appeared in antibiotic-treated cells. Removal of the antibiotics resulted in the recovery of chloroplast number, suggesting that the decrease in number was directly dependent on the antibiotic treatment. Microscopic observations showed that the decrease in the number of chloroplasts resulted from cell division without chloroplast division. These results suggest that enzymes derived from the bacterial peptidoglycan synthesis pathway are related to moss chloroplast division.

Two types of plastid ftsZ genes in the liverwort Marchantia polymorpha

Two types of ftsZ genes (MpftsZ1 and MpftsZ2) were isolated from the liverwort Marchantia polymorpha by degenerate reverse transcription PCR. The MpFtsZ1 and MpFtsZ2 proteins are predicted to localize in chloroplasts. Genomic Southern analysis suggested that each ftsZ gene is a single-copy nuclear gene. Northern analysis confirmed that both genes are active. A phylogenetic tree constructed with the deduced MpFtsZ amino acid sequences suggests that MpFtsZ1 and MpFtsZ2 can be classified into the plant chloroplastic FtsZ1 and FtsZ2 families, respectively. This result suggests that two ftsZ families exist universally in land plants. The determination of the intron structures of both MpftsZ genes supported this hypothesis. The transformation of a sense MpftsZ2 overexpression construct into M. polymorpha produced a large chloroplast phenotype in a transgenic plant. The mean number of chloroplasts was 38.2 (standard deviation, 21.4; n = 200) in epidermal cells of wild-type plants, whereas the mean number of chloroplasts was 7.4 (standard deviation, 4.4; n = 200) in the transgenic plant. Southern analysis showed that the cauliflower mosaic virus 35S promoter- MpftsZ2 construct was inserted in at least three positions. Northern analysis suggested that the high accumulation of MpftsZ2 mRNA blocked plastid division. Determination of the chlorophyll content and the chlorophyll fluorescence parameters suggested that the macrochloroplasts function like chloroplasts in wild-type plants under normal light conditions. However, the transgenic plant grew more slowly than did wild-type plants.

Photosynthetic electron transport regulates the stability of the transcript for the protochlorophyllide oxidoreductase gene in the liverwort, Marchantia paleacea var. diptera

The transfer of Marchantia paleacea var. diptera cells to darkness caused a reversible repression in the accumulation of transcript for a gene, por, encoding the NADPH: protochlorophyllide oxidoreductase (EC 1.3.1.33). The photosynthetic inhibitor DCMU and DBMIB repressed the accumulation in light. In the presence of transcription inhibitor cordycepin, not only incubation in the dark but also addition of DCMU or DBMIB in light stimulated the degradation of the por transcript. These findings suggest that photosynthetic electron transport is involved in regulating the stability of the por transcript.

Characterization of cDNA of the liverwort phytochrome gene, and phytochrome involvement in the light-dependent and light-independent protochlorophyllide oxidoreductase gene expression in Marchantia paleacea var. diptera

The cDNA of the phytochrome gene in the liverwort Marchantia paleacea var. diptera (MpdPHY1) was isolated. MpdPHY1 encoded a conventional phytochrome apoprotein. The MpdPHY1 transcript was accumulated in the dark and suppressed in the light. The degradation of the MpdPHY1 transcript by red light irradiation had red/far-red reversibility, suggesting that the liverwort phytochrome gene expression was regulated by a phytochrome. Northern blot analysis of the transcripts in cells irradiated by red/far-red light revealed that the liverwort phytochrome was involved in the expressions of chlB, chlL, chlN, or por, which encode subunits of light-independent and light-dependent protochlorophyllide oxidoreductase, respectively.

Isolation of a germin-like protein with manganese superoxide dismutase activity from cells of a moss, Barbula unguiculata

A novel extracellular Mn-superoxide dismutase (SOD) was isolated from a moss, Barbula unguiculata. The SOD was a glycoprotein; the apparent molecular mass of its native form was 120 kDa, as estimated by gel filtration chromatography, and that of its monomer was 22,072 Da, as estimated by time of flight mass spectroscopy. The protein had manganese with a stoichiometry of 0.80 Mn/monomer. The cDNA clone for a gene encoding the extracellular Mn-SOD was isolated. Sequence analysis showed that it has a strong similarity to germin (oxalate oxidase) and germin-like proteins (GLPs) of several plant species and possesses all the characteristic features of members of the germin family. The clone encoding this extracellular Mn-SOD was therefore designated B. unguiculata GLP (BuGLP). BuGLP had no oxalate oxidase activity. In addition, the cDNA for a gene encoding the moss mitochondrial Mn-SOD was isolated. Its amino acid sequence had little similarity to that of BuGLP, even though a close similarity was observed among the mitochondrial Mn-SODs of various organisms. BuGLP was the first germin-like protein that was really demonstrated to be a metalloprotein with Mn-SOD activity but no oxalate oxidase activity.

Involvement in denitrification of the napKEFDABC genes encoding the periplasmic nitrate reductase system in the denitrifying phototrophic bacterium Rhodobacter sphaeroides f. sp. denitrificans

Seven genes, napKEFDABC, encoding the periplasmic nitrate reductase system were cloned from the denitrifying phototrophic bacterium Rhodobacter sphaeroides f. sp. denitrificans IL106. Two transmembrane proteins, NapK and NapE, an iron-sulfur protein NapF, a soluble protein NapD, a catalytic subunit of nitrate reductase precursor NapA, a soluble c-type diheme cytochrome precursor NapB, and a membrane-anchored c-type tetraheme cytochrome NapC were deduced as the gene products. Every mutant in which each nap gene was disrupted by omega-cassette insertion lost nitrate reductase activity as well as the ability of cells to grow with nitrate under anaerobic-dark conditions. A transconjugant of the napD-disrupted mutant with a plasmid bearing the napKEFDABC genes recovered both nitrate reductase activity and nitrate-dependent anaerobic-dark growth of cells. Denitrification activity, which was not observed in the napD mutant, was also restored by the conjugation. These results indicate that the periplasmic nitrate reductase encoded by the napKEFDABC genes is the enzyme responsible for denitrification in this phototroph, although the presence of a membrane-bound nitrate reductase has been reported in the same strain.

Differential light regulation of the rbcS gene expression in two cell lines of the liverwort Marchantia paleacea var. diptera

A cDNA of the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) gene (rbcS) was isolated from cells of the liverwort Marchantia paleacea var. diptera. The rbcS was expressed light-independently in a green line, but light-dependently in a yellow line. The accumulation of the large subunit of RuBisCO was regulated cooperatively with that of the small subunit.

Alkyl peroxyl radical-scavenging activity of catechins

Alkyl peroxyl radical (ROO.) generated from the reaction between 20 mM t-butyl hydroperoxide (t-BuOOH) and 200 microM hematin could kill E. coli. The minimum concentrations of catechins sufficient to rescue the bacteria treated with ROO. were found to be 70 microM for (-)-epicatechingallate, 100 microM for (-)-epicatechin and 125 microM for (+)-catechin. These values were comparable with the value of alpha-tocopherol, a typical ROO. scavenger. On the other hand, L-ascorbate and beta-carotene revealed about one tenth the scavenging activity of catechins. No scavenging activity was found for superoxide dismutase even at 86 mM. These facts indicate that catechins have high ROO. scavenging activity.

Light-dependent expression of protochlorophyllide oxidoreductase gene in the liverwort, Marchantia paleacea var. diptera

A cDNA encoding the NADPH:protochlorophyllide oxidoreductase (EC 1.6.99.1) was isolated from suspension-cultured cells of the liverwort, Marchantia paleacea var. diptera. In contrast to the situation in most higher plants, the liverwort gene was expressed in a light-dependent manner.

Characterization of a cDNA encoding CuZn-superoxide dismutase from the liverwort Marchantia paleacea var. diptera

Suspension-cultured cells of the liverwort Marchantia paleacea var. diptera contain a cytosolic CuZn-superoxide dismutase (SOD) whose N-terminal amino acid sequence is similar to those of the isozymes found in chloroplasts of higher plants [Tanaka et al. (1996) Plant Cell Physiol. 37: 523]. A cDNA (MSODCc) encoding the cytosolic CuZn-SOD was isolated from cDNA library constructed from a liverwort cell suspension culture. The deduced amino acid sequence showed a higher degree of homology with the sequences of CuZn-SODs in chloroplasts than those in the cytosol of higher plants and an unique additional peptide in the C-terminal region, but no plastid transit sequence. Northern blotting using MSODCc as a probe and immunoblot analysis with antiserum against the enzyme revealed that the steady state level of transcript was not affected by copper, but both CuZn-SOD protein and its activity increased.

Purification of the cytosolic CuZn-superoxide dismutase (CuZn-SOD) of Marchantia paleacea var. diptera and its resemblance to CuZn-SOD from chloroplasts

Suspension-cultured cells of Marchantia paleacea var. diptera contain a single form of CuZn-superoxide dismutase (SOD; EC 1.15.1.1) which is localized in the cytosol. SOD activity was found in cells cultured under heterotrophic, photoheterotrophic and photoautotrophic conditions. The CuZn-SOD was purified to homogeneity from liverwort cells that had been cultured heterotrophically. Its molecular mass was 32.6 kDa, and it contained 17.5 dDa subunits, an indication that the enzyme is a homodimer. The enzyme had peaks of absorption at 252, 258 and 264 nm in the ultraviolet region, due to the presence of phenylalanine, and a peak at 680 nm in the visible region, which is characteristic of CuZn-SODs from chloroplasts. The amino acid sequence of the amino-terminal region of the enzyme exhibited a very high degree of homology to those of chloroplast CuZn-SODs. An antiserum raised against the CuZn-SOD from liverwort cross-reacted more strongly with the enzyme from spinach chloroplasts, than with the enzyme from spinach cytosol. These results indicate that the CuZn-SOD of liverwort resembles CuZn-SOD in chloroplasts even though the former is located in the cytosol.

Photosynthetic ability in dark-grown Reboulia hemisphaerica and Barbula unguiculata cells in suspension culture

Suspension cultured cells of the liverwort, Reboulia hemisphaerica and of the moss, Barbula unguiculata were independently subcultured in the medium containing 2% glucose in the dark or in the light for more than one year, and the photosynthetic activities of the final cultures were determined. Throughout the culture period light-grown cells of both species contained high amount of chlorophyll (4 to 34 μg mg(-1) dry weight) and showed a high photosynthetic activity (10 to 84 μmol O2 mg(-1) chlorophyll h(-1)). Dark-grown cells of R. hemisphaerica showed the same level of chlorophyll content and photosynthetic O2 evolving activity as light-grown cells. Although chlorophyll content in dark-grown B. unguiculata cells was ten-fold lower than that in light-grown cells, the photosynthetic activity of these dark-grown cells was higher than that of light-grown cells based on chlorophyll content.

Effect of cytokinin on morphological changes of suspension cultured cells of the moss, Barbula unguiculata

Suspension cultured cells of the moss, Barbula unguiculata, grow actively in both light and dark culture. Light-grown cells contain chlorophyll and exhibit an undifferentiated callus form. When cells are transferred to a dark condition, they develop into protonemata. Protonemata formation in the dark can be inhibited by the addition of 5 μM benzyladenine or 6-furfurylaminopurine but is not affected by the addition of 5 μM 2,4-dichlorophenoxyacetic acid or naphthalene acetic acid.