Non-invasive quantitative detection and applications of non-toxic, S65T-type green fluorescent protein in living plants

Expression of rice heat stress transcription factor OsHsfA2e enhances tolerance to environmental stresses in transgenic Arabidopsis

Plant growth and crop yields are limited by high-temperature stresses. In this study, we attempted to isolate the rice genes responsible for high-temperature stress tolerance using a transformed Arabidopsis population expressing a full-length cDNA library of rice. From approximately 20,000 lines of transgenic Arabidopsis, we isolated a thermotolerant line, R04333, that could survive transient heat stress at the cotyledon stage. The rice cDNA inserted in R04333 encodes OsHsfA2e, a member of the heat stress transcription factors. The thermotolerant phenotype was observed in newly constructed transgenic Arabidopsis plants expressing OsHsfA2e. Among 5 A2-type HSF genes encoded in the rice genome, four genes, including OsHsfA2e, are induced by high temperatures in rice seedlings. The OsHsfA2e protein was localized to the nuclear region and exhibited transcription activation activity in the C-terminal region. Microarray analysis demonstrated that under unstressed conditions transgenic Arabidopsis overexpressing OsHsfA2e highly expressed certain stress-associated genes, including several classes of heat-shock proteins. The thermotolerant phenotype was observed not only in the cotyledons but also in rosette leaves, inflorescence stems and seeds. In addition, transgenic Arabidopsis exhibited tolerance to high-salinity stress. These observations suggest that the OsHsfA2e may be useful in molecular breeding designed to improve the environmental stress tolerance of crops.

The N-terminal presequence from F1-ATPase β-subunit of Nicotiana plumbaginifolia efficiently targets green fluorescent fusion protein to the mitochondria in diverse commercial crops

Approximately 10-15% of plant nuclear genes appear to encode mitochondrial proteins that are directed to mitochondria by specific targeting signals. Reports on the heterologous function of these targeting signals are generally limited to one or a few species, with an emphasis on model plants such as tobacco and Arabidopsis. Given their sequence diversity and their insufficient testing in commercially important crops (including monocotyledonous crops), the extent to which these signals can be relied on for biotechnological purposes across species remains to be established. This study provides the experimental verification of a mitochondrial signal that is functional across diverse crop species, including five monocots (sugarcane, wheat, corn, sorghum and onion) and seven dicots (cucumber, cauliflower, tomato, capsicum, pumpkin, coriander and sunflower). In all 12 crops, transient assays following microprojectile bombardment showed that the N-terminal mitochondrial presequence from F₁-ATPase β-subunit (ATPase-β) of Nicotiana plumbaginifolia Viv. targeted green fluorescent fusion protein to the mitochondria. The transient assay results in sugarcane were confirmed in stably transformed root cells. The ATPase-β signal should be a useful metabolic engineering tool for directing recombinant proteins to the mitochondrial matrix in diverse plant species of commercial interest.

Polyubiquitin promoter-based binary vectors for overexpression and gene silencing in Lotus japonicus

In this study, we compared the transcriptional activities between Cauliflower mosaic virus (CaMV)35S promoter and polyubiquitin (Ljubq1) promoter from Lotus japonicus using beta-glucuronidase (gus) reporter gene in transgenic plants of L. japonicus. The promoter analysis demonstrated that the Ljubq1 promoter possessed higher activity than the CaMV35S promoter in leaves, stems, roots, nodules, and pollen. Finally, we created GATEWAY conversion technology-compatible binary vectors for over-expression and RNA interference under the Ljubq1 promoter. These materials could provide alternative choice for studies in L. japonicus.

The Arabidopsis Phosphatidylinositol Phosphate 5-Kinase PIP5K3 is a key regulator of root hair tip growth

Phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] functions as a site-specific signal on membranes to promote cytoskeletal reorganization and membrane trafficking. Localization of PtdIns(4,5)P2 to apices of growing root hairs and pollen tubes suggests that it plays an important role in tip growth. However, its regulation and mode of action remain unclear. We found that Arabidopsis thaliana PIP5K3 (for Phosphatidylinositol Phosphate 5-Kinase 3) encodes a phosphatidylinositol 4-phosphate 5-kinase, a key enzyme producing PtdIns(4,5)P2, that is preferentially expressed in growing root hairs. T-DNA insertion mutations that substantially reduced the expression of PIP5K3 caused significantly shorter root hairs than in the wild type. By contrast, overexpression caused longer root hairs and multiple protruding sites on a single trichoblast. A yellow fluorescent protein (YFP) fusion of PIP5K3, driven by the PIP5K3 promoter, complemented the short-root-hair phenotype. PIP5K3-YFP localized to the plasma membrane and cytoplasmic space of elongating root hair apices, to growing root hair bulges, and, notably, to sites about to form root hair bulges. The signal was greatest in rapidly growing root hairs and quickly disappeared when elongation ceased. These results provide evidence that PIP5K3 is involved in localizing PtdIns(4,5)P2 to the elongating root hair apex and is a key regulator of the machinery that initiates and promotes root hair tip growth.

The ensemble of hetero-proteins in inorganic nanochannels

The assembly and proper alignment of two heterofluorescent proteins (sGFP and DsRed) in the mesoporous channels of ethanol-treated FSM6.2 (a folded-sheet mesoporous material with a pore diameter of 6.2 nm) was confirmed using a fluorescence resonance energy transfer (FRET) technique. The sGFP-DsRed-FSM6.2 conjugate showed a large decrease in the emission of donor (sGFP) fluorescence, indicating that the conjugate functions as an energy transfer system through the combination of the two heteroproteins, due to the successful encapsulation of the sGFP-DsRed pairs in the mesopores. Fluorescence spectral analysis demonstrated that the proteins were highly dispersed and homogeneously encapsulated in the mesopores of FSM6.2, even at high concentration, although they spontaneously aggregated and showed a red shift in solution at the concentration corresponding to that in the conjugate. Furthermore, an increase in the amount of sGFP and DsRed adsorbed to the pores of FSM6.2 led to a decrease in the distance between these proteins, resulting in enhancement of FRET efficiency.

Leaf positioning of Arabidopsis in response to blue light

Appropriate leaf positioning is essential for optimizing photosynthesis and plant growth. However, it has not been elucidated how green leaves reach and maintain their position for capturing light. We show here the regulation of leaf positioning under blue light stimuli. When 1-week-old Arabidopsis seedlings grown under white light were transferred to red light (25 micromol m(-2) s(-1)) for 5 d, new petioles that appeared were almost horizontal and their leaves were curled and slanted downward. However, when a weak blue light from above (0.1 micromol m(-2) s(-1)) was superimposed on red light, the new petioles grew obliquely upward and the leaves were flat and horizontal. The leaf positioning required both phototropin1 (phot1) and nonphototropic hypocotyl 3 (NPH3), and resulted in enhanced plant growth. In an nph3 mutant, neither optimal leaf positioning nor leaf flattening by blue light was found, and blue light-induced growth enhancement was drastically reduced. When blue light was increased from 0.1 to 5 micromol m(-2) s(-1), normal leaf positioning and leaf flattening were induced in both phot1 and nph3 mutants, suggesting that phot2 signaling became functional and that the signaling was independent of phot1 and NPH3 in these responses. When plants were irradiated with blue light (0.1 micromol m(-2) s(-1)) from the side and red light from above, the new leaves became oriented toward the source of blue light. When we transferred these plants to both blue light and red light from above, the leaf surface changed its orientation to the new blue light source within a few hours, whereas the petioles initially were unchanged but then gradually rotated, suggesting the plasticity of leaf positioning in response to blue light. We showed the tissue expression of NPH3 and its plasma membrane localization via the coiled-coil domain and the C-terminal region. We conclude that NPH3-mediated phototropin signaling optimizes the efficiency of light perception by inducing both optimal leaf positioning and leaf flattening, and enhances plant growth.

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.

Functional analysis of N-terminal domains of Arabidopsis chlorophyllide a oxygenase

Higher plants acclimate to various light environments by changing the antenna size of a light-harvesting photosystem. The antenna size of a photosystem is partly determined by the amount of chlorophyll b in the light-harvesting complexes. Chlorophyllide a oxygenase (CAO) converts chlorophyll a to chlorophyll b in a two-step oxygenation reaction. In our previous study, we demonstrated that the cellular level of the CAO protein controls accumulation of chlorophyll b. We found that the amino acids sequences of CAO in higher plants consist of three domains (A, B, and C domains). The C domain exhibits a catalytic function, and we demonstrated that the combination of the A and B domains regulates the cellular level of CAO. However, the individual function of each of A and B domain has not been determined yet. Therefore, in the present study we constructed a series of deleted CAO sequences that were fused with green fluorescent protein and overexpressed in a chlorophyll b-less mutant of Arabidopsis thaliana, ch1-1, to further dissect functions of A and B domains. Subsequent comparative analyses of the transgenic plants overexpressing B domain containing proteins and those lacking the B domain determined that there was no significant difference in CAO protein levels. These results indicate that the B domain is not involved in the regulation of the CAO protein levels. Taken together, we concluded that the A domain alone is involved in the regulatory mechanism of the CAO protein levels.

RING-H2 type ubiquitin ligase EL5 is involved in root development through the maintenance of cell viability in rice

Rice EL5 is an ATL family gene characterized by a transmembrane domain at the N-terminal and a RING-H2 finger domain (RFD), which exhibits ubiquitin ligase (E3) activity. To elucidate the physiological roles of EL5, we analyzed transgenic rice plants overexpressing mutant EL5 proteins that are impaired in E3 activity to various degrees. Plants expressing EL5C153A and EL5W165A, which encode an inactive E3, showed a rootless phenotype accompanied by cell death in root primordia, and those expressing EL5V162A, with moderately impaired E3 activity, formed short crown roots with necrotic lateral roots. The dominant-negative phenotype was specifically observed in root meristems where EL5 is expressed, and not recovered by exogenous auxin. When wild-type EL5 was transcriptionally overexpressed, the EL5 protein was barely detected by Western blotting. Neither treatment with a proteasome inhibitor nor mutation of the sole lysine residue, a potential target of ubiquitination, resulted in increased EL5 accumulation, whereas mutations in the RFD led to increased EL5 accumulation. The stabilized EL5 without the RFD was localized in the plasma membrane. Deletion of the transmembrane domain prevented the EL5 from localizing in the membrane and from exerting an inhibitory effect on root formation. Deletion of the C-terminal region also neutralized the negative effect. We concluded that EL5 plays a major role as a membrane-anchored E3 for the maintenance of cell viability after the initiation of root primordial formation. In addition, we propose that EL5 is an unstable protein, of which degradation is regulated by the RFD in a proteasome-independent manner.

A nitrite transporter associated with nitrite uptake by higher plant chloroplasts

Chloroplasts take up cytosolic nitrite during nitrate assimilation. In this study we identified a nitrite transporter located in the chloroplasts of higher plants. The transporter, CsNitr1-L, a member of the proton-dependent oligopeptide transporter (POT) family, was detected during light-induced chloroplast development in de-etiolating cucumber seedlings. We detected a CsNitr1-L-green fluorescent protein (GFP) fusion protein in the chloroplasts of leaf cells and found that an immunoreactive 51 kDa protein was present in the isolated inner envelope membrane of chloroplasts. CsNitr1-L has an isoform, CsNitr1-S, with an identical 484 amino acid core sequence; however, in CsNitr1-S the 120 amino acid N-terminal extension is missing. Saccharomyces cerevisiae cells expressing CsNitr1-S absorbed nitrite from an acidic medium at a slower rate than mock-transformed control cells, and accumulated nitrite to only one-sixth the concentration of the control cells, suggesting that CsNitr1-S enhances the efflux of nitrite from the cell. Insertion of T-DNA in a single CsNitr1-L homolog (At1g68570) in Arabidopsis resulted in nitrite accumulation in leaves to more than five times the concentration found in the wild type. These results show that it is possible that both CsNitr1-L and CsNitr1-S encode efflux-type nitrite transporters, but with different subcellular localizations. CsNitr1-L may possibly load cytosolic nitrite into chloroplast stroma in the chloroplast envelope during nitrate assimilation. The presence of genes homologous to CsNitr1-L in the genomes of Arabidopsis and rice indicates that facilitated nitrite transport is of general physiological importance in plant nutrition.

Excessive expression of the plant kinesin TBK5 converts cortical and perinuclear microtubules into a radial array emanating from a single focus

TBK5 is a plant-specific kinesin constantly expressed in tobacco BY-2 cells. An analysis of the distribution of green fluorescent protein-tagged TBK5 (GFP-TBK5) transiently expressed in BY-2 protoplasts revealed that TBK5 could associate with microtubules in vivo. GFP-TBK5 often assembled to form a single particle when accumulated in cells. The particle was located in close proximity to the nucleus, and its formation was accompanied by the development of a radial array of microtubules emanating from it and the loss of cortical microtubules. Microtubule depolymerization by treatment with propyzamide inhibited particle formation and stimulated the formation of dispersed aggregates of GFP-TBK5. Through expression of different TBK5 mutants as GFP fusions, the motor domain, two separated coiled-coil domains and the C-terminal domain of TBK5 were identified as the domains playing essential roles in particle formation. Mutants with putatively non-motile motor domains or lacking the C-terminal domain were localized to cortical and perinuclear microtubules, whereas those lacking either of the coiled-coil domains were preferentially distributed around the nucleus and along perinuclar microtubules. Further, the deletion of one of the coiled-coil domains or the C-terminal domain was sufficient to inhibit the propyzamide-induced formation of dispersed aggregates, whereas the mutation in the motor domain was not. These results led us to propose a model in which the particle is formed through the microtubule-based movement of GFP-TBK5 toward the nucleus and subsequent microtubule-independent aggregation based on coiled-coil interactions. The dramatic microtubule rearrangement would be explained if GFP-TBK5 relocated and gathered newly formed microtubules and/or microtubule-nucleating units.

Elicitin-responsive lectin-like receptor kinase genes in BY-2 cells

The inhibition of elicitor-induced plant defense responses by the protein kinase inhibitors K252a and staurosporine indicates that defense responses require protein phosphorylation. We isolated a cDNA clone encoding Nicotiana tabacum lectin-like receptor protein kinase 1 (NtlecRK1), an elicitor-responsive gene; in tobacco bright yellow (BY-2) cells by a differential display method. NtlecRK forms a gene family with at least three members in tobacco. All three NtlecRK genes potentially encode the N-terminal legume lectin domain, transmembrane domain and C-terminal Ser/Thr-type protein kinase domain. Green fluorescent protein (GFP) fusion showed that the NtlecRK1 protein was located on the plasma membrane. In addition, NtlecRK1 and 3 were responsive to INF1 elicitin and the bacterial elicitor harpin. These results indicate that NtlecRKs are membrane-located protein kinases that are induced during defense responses in BY-2 cells.

Suppressor of RNA silencing encoded by the monopartite tomato leaf curl Java begomovirus

We previously isolated the monopartite begomovirus tomato leaf curl Java virus (ToLCJAV) and satellite DNAbeta02 from the same naturally infected tomato source in Indonesia. ToLCJAV induced mild leaf curl symptoms in Nicotiana benthamiana plants; DNAbeta02 encoded the betaC1 gene and produced severe leaf curl symptoms when co-inoculated with ToLCJAV in N. benthamiana. However, DNAbeta02mbetaC1, which contains a frame shift mutation, did not induce severe symptoms in N. benthamiana when co-inoculated with ToLCJAV. Expression of the betaC1 gene in N. benthamiana using a potato virus X (PVX) vector induced virus-like symptoms in the absence of ToLCJAV infection. When betaC1 and green fluorescent protein (GFP) genes were co-expressed in the GFP-expressing N. benthamiana line 16c from a PVX vector, betaC1 was able to suppress posttranscriptional gene silencing (PTGS) induced by GFP and eliminated the short interfering RNA (siRNA) associated with GFP expression, with a correlated increase in GFP mRNA accumulation. When C2 or C4 genes of ToLCJAV and the GFP gene were co-expressed in the GFP-expressing N. benthamiana line 16c, C2 showed a weak suppressor activity and C4 was unable to suppress PTGS induced by GFP, and siRNA associated with GFP was detected. The results of the sub-cellular localization of ToLCJAV-betaC1 in the epidermal cells of N. benthamiana and onion tissues showed that this protein is accumulated towards the periphery of the cell.

LjnsRING, a novel RING finger protein, is required for symbiotic interactions between Mesorhizobium loti and Lotus japonicus

Nodule-specific (nodulin) genes are thought to play crucial roles during establishment of the nitrogen-fixing symbiosis between legume plants and Rhizobium bacteria. On the basis of a gene expression database for early stages of the nodulation process of Lotus japonicus, previously constructed by a cDNA macroarray analysis, we identified a novel nodulin gene, LjnsRING, which encodes a protein with a typical RING-H2 finger domain that is well conserved in a number of plant E3 ubiquitin ligases. LjnsRING transcripts were almost exclusively expressed in nodules, and very low expression was detected in roots and shoots. RNA interference (RNAi) knockdown of LjnsRING by hairy root transformation caused impaired root growth together with abortion of nodule formation. Examination with lacZ-labeled Mesorhizobium loti indicated that infection thread formation in the RNAi transgenic hairy roots was significantly inhibited. Analysis using a chimeric gene of LjnsRING promoter and beta-glucuronidase (GUS) coding region demonstrated that LjnsRING transcription in nodules was restricted to the infected cells. These results suggest the requirement for LjnsRING in rhizobial infection and the subsequent nodule formation process.

Molecular characterization of four rice genes encoding ethylene-responsive transcriptional factors and their expressions in response to biotic and abiotic stress

We isolated and identified four rice genes, OsBIERF1 to OsBIERF4 (Oryza sativa benzothiadiazole (BTH)-induced ethylene responsive transcriptional factors (ERF)) and analyzed their expressions in rice disease resistance response and under various abiotic stress conditions. The OsBIERF1-4 proteins contain conserved ERF domains, but are categorized into different classes of the previously characterized ERF proteins based on their structural organizations. OsBIERF3 and OsBIERF2 belong to Classes I and II, respectively; while OsBIRERF1 and OsBIERF4 are members of Class IV. OsBIERF3 could bind specifically to the GCC box sequence and was targeted to nucleus when transiently expressed in onion epidermis cells. Expression of OsBIERF1, OsBIERF3 and OsBIERF4 was induced by treatments with BTH and salicylic acid, chemical inducers capable of inducing disease resistance response in rice. In the BTH-treated rice seedlings, expression of OsBIERF1, OsBIERF3 and OsBIERF4 was further induced by infection with Magnaporthe grisea, the rice blast fungus, as compared with those in water-treated seedlings. OsBIERF1 and OsBIERF3 were activated in an incompatible interaction but not in compatible interaction between rice and M. grisea. Moreover, OsBIERF1, OsBIERF3 and OsBIERF4 were also up-regulated by salt, cold, drought and wounding. These results suggest that OsBIERF proteins may participate in different signaling pathways that mediate disease resistance response and stress responses to abiotic factors.

Rice plastidial N-glycosylated nucleotide pyrophosphatase/phosphodiesterase is transported from the ER-golgi to the chloroplast through the secretory pathway

A nucleotide pyrophosphatase/phosphodiesterase (NPP) activity that catalyzes the hydrolytic breakdown of ADP-glucose (ADPG) has been shown to occur in the plastidial compartment of both mono- and dicotyledonous plants. To learn more about this enzyme, we purified two NPPs from rice (Oryza sativa) and barley (Hordeum vulgare) seedlings. Both enzymes are glycosylated, since they bind to concanavalin A, stain with periodic acid-Schiff reagent, and are digested by Endo-H. A complete rice NPP cDNA, designated as NPP1, was isolated, characterized, and overexpressed in transgenic plants displaying high ADPG hydrolytic activity. Databank searches revealed that NPP1 belongs to a functionally divergent group of plant nucleotide hydrolases. NPP1 contains numerous N-glycosylation sites and a cleavable hydrophobic signal sequence that does not match with the N-terminal part of the mature protein. Both immunocytochemical analyses and confocal fluorescence microscopy of rice cells expressing NPP1 fused with green fluorescent protein (GFP) revealed that NPP1-GFP occurs in the plastidial compartment. Brefeldin A treatment of NPP1-GFP-expressing cells prevented NPP1-GFP accumulation in the chloroplasts. Endo-H digestibility studies revealed that both NPP1 and NPP1-GFP in the chloroplast are glycosylated. Collectively, these data demonstrate the trafficking of glycosylated proteins from the endoplasmic reticulum-Golgi system to the chloroplast in higher plants.

Early infection of scutellum tissue with Agrobacterium allows high-speed transformation of rice

Several approaches have recently been adopted to improve Agrobacterium-mediated transformation of rice, both to generate the large number of T-DNA insertion plants needed for functional analysis of the rice genome, and for production of rice with additional agronomical value. However, about 3 months of in vitro culture is still required for isolation of transgenic rice plants. Here, we report the competency of scutellum tissue from 1-day pre-cultured seeds for Agrobacterium-mediated transformation. Furthermore, early infection of rice seeds with Agrobacterium enhanced efficient selection of transformed calli. Using our system, we successfully regenerated transgenic rice plantlets within a month of the start of the aseptic culture of mature seeds. Our new system should reduce the somaclonal variation accompanying prolonged culture of rice cells in the dedifferentiated state and facilitate the molecular breeding of rice.

Protein phosphatase 1 positively regulates stomatal opening in response to blue light in Vicia faba

Phototropins, plant blue light receptors, mediate stomatal opening through the activation of the plasma membrane H(+)-ATPase by unknown mechanisms. Here we report that type 1 protein phosphatase (PP1) positively regulates the blue light signaling between phototropins and the H(+)-ATPase in guard cells of Vicia faba. We cloned the four catalytic subunits of PP1 (PP1c) from guard cells and determined the expression of the isoforms in various tissues. Transformation of Vicia guard cells with PP1c isoforms that had lost enzymatic activity by one amino acid mutation, or with human inhibitor-2, a specific inhibitor protein of PP1c, suppressed blue light-induced stomatal opening. Addition of fusicoccin, an activator of the plasma membrane H(+)-ATPase, to these transformed guard cells induced normal stomatal opening, suggesting that the transformations did not affect the basic mechanisms for stomatal opening. Tautomycin, an inhibitor of PP1, inhibited blue light-induced H(+) pumping, phosphorylation of the plasma membrane H(+)-ATPase in guard cell protoplasts, and stomatal opening. However, tautomycin did not inhibit the blue light-dependent phosphorylation of phototropins. We conclude that PP1 functions downstream of phototropins and upstream of the H(+)-ATPase in the blue light signaling pathway of guard cells.

Functional conservation of cold shock domains in bacteria and higher plants

In Escherichia coli, a family of cold shock proteins (CSPs) function as transcription antiterminators or translational enhancers at low temperature by destabilizing RNA secondary structure. A wheat nucleic acid-binding protein (WCSP1) was found to contain a cold shock domain (CSD) bearing high similarity to E. coli cold shock proteins. In the present study, a series of mutations were introduced into WCSP1, and its functionality was investigated by using in vivo and in vitro assays in the context of functional conservation with E. coli CSPs. Constitutive expression of WT WCSP1 in an E. coli cspA, cspB, cspE, cspG quadruple deletion mutant complemented its cold-sensitive phenotype, suggesting that WCSP1 shares a function with E. coli CSPs for cold adaptation. In addition, transcription antitermination activity was demonstrated for WCSP1 by using an E. coli strain that has a hairpin loop upstream of a chloramphenicol resistance gene. In vitro dsDNA melting assays clearly demonstrated that WCSP1 melts dsDNA, an activity that was positively correlated to the ability to bind ssDNA. When mutations were introduced at critical residues within the consensus RNA binding motifs (RNP1 and RNP2) of WCSP1, it failed to melt dsDNA. Studies with WCSP1-GFP fusion proteins documented patterns that are consistent with ER and nuclear localization. In vivo and in vitro functional analyses, coupled with subcellular localization data, suggest that WCSP1 may function as a RNA chaperone to destabilize secondary structure and is involved in the regulation of translation under low temperature.

Functional analysis of an Arabidopsis transcription factor, DREB2A, involved in drought-responsive gene expression

Transcription factors DREB1A/CBF3 and DREB2A specifically interact with cis-acting dehydration-responsive element/C-repeat (DRE/CRT) involved in cold and drought stress-responsive gene expression in Arabidopsis thaliana. Intact DREB2A expression does not activate downstream genes under normal growth conditions, suggesting that DREB2A requires posttranslational modification for activation, but the activation mechanism has not been clarified. DREB2A domain analysis using Arabidopsis protoplasts identified a transcriptional activation domain between residues 254 and 335, and deletion of a region between residues 136 and 165 transforms DREB2A to a constitutive active form. Overexpression of constitutive active DREB2A resulted in significant drought stress tolerance but only slight freezing tolerance in transgenic Arabidopsis plants. Microarray and RNA gel blot analyses revealed that DREB2A regulates expression of many water stress-inducible genes. However, some genes downstream of DREB2A are not downstream of DREB1A, which also recognizes DRE/CRT but functions in cold stress-responsive gene expression. Synthetic green fluorescent protein gave a strong signal in the nucleus under unstressed control conditions when fused to constitutive active DREB2A but only a weak signal when fused to full-length DREB2A. The region between DREB2A residues 136 and 165 plays a role in the stability of this protein in the nucleus, which is important for protein activation.

Laser-induced fluorescence imaging and spectroscopy of GFP transgenic plants

Green fluorescent protein (GFP) and other fluorescent protein bioreporters can be used to monitor transgenes in plants. GFP is a valuable marker for transgene presence and expression, but remote sensing instrumentation for stand-off detection has lagged behind fluorescent protein marker biotechnology. However, both biology and photonics are needed for the monitoring technology to be fully realized. In this paper, we describe laser-induced fluorescence imaging and laser-induced fluorescence spectroscopy of GFP-transgenic plants in ambient light towards the application of remote sensing of transgenic plants producing GFP.

Arabidopsis Mutants by Activation Tagging in which Photosynthesis Genes are Expressed in Dedifferentiated Calli

In an effort to delineate the precise mechanisms underlying the organ-specific expression of photosynthesis genes, Arabidopsis lines homozygous for each transgene construct made with the gene for hygromycin B phosphotransferase or beta-glucuronidase (GUS) placed under control of the promoter of the nuclear gene for the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (RBCS-3B) were constructed. Furthermore, activation tagging with T-DNA possessing quadruply repeated enhancers derived from the cauliflower mosaic virus 35S promoter was applied to a transgenic line of Arabidopsis. Mutants resistant to hygromycin B during the growth of calli generated from non-green roots on callus-inducing medium resulted from the expression of hygromycin B phosphotransferase driven by the RBCS-3B promoter. Three mutant lines, ces101 to ces103 (callus expression of RBCS), were obtained from approximately 4,000 calli resistant to a selectable marker for transformation. The active transcription driven by the RBCS-3B promoter in all the calli of ces mutants was confirmed by expression of both the GUS reporter gene and endogenous RBCS-3B. Chlorophyll and carotenoids, as well as light-dependent O(2) evolution, have been detected in the calli of all ces mutants. The loci where T-DNA was integrated in the ces101 line were determined by thermal asymmetric interlaced (TAIL)-PCR. The introduction of a DNA fragment harboring the gene for receptor-like kinase placed under the influence of enhancers into the parental line reproduced the phenotype of ces mutants. We have thus concluded that CES101 is a receptor-like kinase. The strategy presented in this investigation may promise to select a greater number of ces mutants.

The A-type cyclin CYCA2;3 is a key regulator of ploidy levels in Arabidopsis endoreduplication

Plant cells frequently undergo endoreduplication, a process in which chromosomal DNA is successively duplicated in the absence of mitosis. It has been proposed that endoreduplication is regulated at its entry by mitotic cyclin-dependent kinase activity. However, the regulatory mechanisms for its termination remain unclear, although plants tightly control the ploidy level in each cell type. In the process of searching for regulatory factors of endoreduplication, the promoter of an Arabidopsis thaliana cyclin A gene, CYCA2;3, was revealed to be active in developing trichomes during the termination period of endoreduplication as well as in proliferating tissues. Taking advantage of the situation that plants encode highly redundant cyclin A genes, we were able to perform functional dissection of CYCA2;3 using null mutant alleles. Null mutations of CYCA2;3 semidominantly promoted endocycles and increased the ploidy levels achieved in mature organs, but they did not significantly affect the proportion of cells that underwent endoreduplication. Consistent with this result, expression of the CYCA2;3-green fluorescent protein fusion protein restrained endocycles in a dose-dependent manner. Moreover, a mutation in the destruction box of CYCA2;3 stabilized the fusion protein in the nuclei and enhanced the restraint. We conclude that CYCA2;3 negatively regulates endocycles and acts as a key regulator of ploidy levels in Arabidopsis endoreduplication.

Plant mitochondrial dynamics

Higher plant mitochondria are dynamic, pleomorphic organelles. The higher plant chondriome (all mitochondria in a cell collectively) is typically composed of numerous, physically discrete, mitochondria. However, frequent inter-mitochondrial fusion, enabling the mixing and recombination of mtDNA, ensures that the higher plant chondriome functions, at least genetically, as a discontinuous whole. Nothing is known about the genes controlling mitochondrial fusion in plants; there are no plant homologues of most of the genes known to be involved in fusion in other organisms. In contrast, the mitochondrial fission apparatus is generally conserved. Higher plant mitochondria use dynamin-like and Fis-type proteins for division; like yeast and animals, higher plants have lost the mitochondrial-specific form of the prokaryote-derived protein, FtsZ. In addition to being providers of energy for life, mitochondria provide a trigger for death. The role of mitochondrial dynamics in the initiation and promulgation of cell death is conserved in higher plants although there are specific differences in the genes and mechanisms involved relative to other higher eukaryotes.

Molecular cloning, functional expression and subcellular localization of two putative vacuolar voltage-gated chloride channels in rice (Oryza sativa L.)

We isolated two cDNA clones (OsCLC-1 and OsCLC-2) homologous to tobacco CLC-Nt1, which encodes a voltage-gated chloride channel, from rice (Oryza sativa L. ssp. japonica, cv. Nipponbare). The deduced amino acid sequences were highly conserved (87.9% identity with each other). Southern blot analysis of the rice genomic DNA revealed that OsCLC-1 and OsCLC-2 were single-copy genes on chromosomes 4 and 2, respectively. OsCLC-1 was expressed in most tissues, whereas OsCLC-2 was expressed only in the roots, nodes, internodes and leaf sheaths. The level of expression of OsCLC-1, but not of OsCLC-2, was increased by treatment with NaCl. Both genes could partly substitute for GEF1, which encodes the sole chloride channel in yeast, by restoring growth under ionic stress. These results indicate that both genes are chloride channel genes. The proteins from both genes were immunochemically detected in the tonoplast fraction. Tagged synthetic green fluorescent protein which was fused to OsCLC-1 or OsCLC-2 localized in the vacuolar membranes. These results indicate that the proteins may play a role in the transport of chloride ions across the vacuolar membrane. We isolated loss-of-function mutants of both genes from a panel of rice mutants produced by the insertion of a retrotransposon, Tos17, in the exon region, and found inhibition of growth at all life stages.

Localization of a flavonoid biosynthetic polyphenol oxidase in vacuoles

Aureusidin synthase, a polyphenol oxidase (PPO), specifically catalyzes the oxidative formation of aurones from chalcones, which are plant flavonoids, and is responsible for the yellow coloration of snapdragon (Antirrhinum majus) flowers. All known PPOs have been found to be localized in plastids, whereas flavonoid biosynthesis is thought to take place in the cytoplasm [or on the cytoplasmic surface of the endoplasmic reticulum (ER)]. However, the primary structural characteristics of aureusidin synthase and some of its molecular properties argue against localization of the enzyme in plastids and the cytoplasm. In this study, the subcellular localization of the enzyme in petal cells of the yellow snapdragon was investigated. Sucrose-density gradient and differential centrifugation analyses suggested that the enzyme (the 39-kDa mature form) is not located in plastids or on the ER. Transient assays using a green fluorescent protein (GFP) chimera fused with the putative propeptide of the PPO precursor suggested that the enzyme was localized within the vacuole lumen. We also found that the necessary information for vacuolar targeting of the PPO was encoded within the 53-residue N-terminal sequence (NTPP), but not in the C-terminal sequence of the precursor. NTPP-mediated ER-to-Golgi trafficking to vacuoles was confirmed by means of the co-expression of an NTPP-GFP chimera with a dominant negative mutant of the Arabidopsis GTPase Sar1 or with a monomeric red fluorescent protein (mRFP)-fused Golgi marker (an H+-translocating inorganic pyrophosphatase of Arabidopsis). We identified a sequence-specific vacuolar sorting determinant in the NTPP of the precursor. We have demonstrated the biosynthesis of a flavonoid skeleton in vacuoles. The findings of this metabolic compartmentation may provide a strategy for overcoming the biochemical instability of the precursor chalcones in the cytoplasm, thus leading to the efficient accumulation of aurones in the flower.

Hairy root-activation tagging: a high-throughput system for activation tagging in transformed hairy roots

Activation tagging is a powerful technique for generating gain-of-function mutants in plants. We developed a new vector system for activation tagging of genes in "transformed hairy roots". The binary vector pHR-AT (Hairy Root-Activation Tagging) and its derivative pHR-AT-GFP contain a cluster of rol (rooting locus) genes together with the right border facing four tandem repeats of the cauliflower mosaic virus (CaMV) 35S enhancer element on the same T-DNA. Transformation experiments using Arabidopsis, potato, and tobacco as model plants revealed that upon inoculating plants with Agrobacterium tumefaciens harboring these vectors, a large number of independently transformed roots could be induced from explants within a short period of time, and root culture lines were subsequently established. Molecular analyses of the pHR-AT-GFP-transformed Arabidopsis lines showed that expression of the genes adjacent to the T-DNA insertion site was significantly increased. This system may facilitate application of the activation-tagging approach to plant species that are recalcitrant to the regeneration of transgenic plants. High-throughput metabolic profiling of activation-tagged root culture lines will offer opportunities for identifying regulatory or biosynthetic genes for the production of valuable secondary metabolites of interest.

Consistent transcriptional silencing of 35S-driven transgenes in gentian

In this study, no transgenic gentian (Gentiana triflora x Gentiana scabra) plants produced via Agrobacterium-mediated transformation exhibited transgene (GtMADS, gentian-derived MADS-box genes or sGFP, green fluorescent protein) expression in their leaf tissues, despite the use of constitutive Cauliflower mosaic virus (CaMV) 35S promoter. Strikingly, no expression of the selectable marker gene (bar) used for bialaphos selection was observed. To investigate the possible cause of this drastic transgene silencing, methylation-specific sequences were analysed by bisulfite genomic sequencing using tobacco transformants as a control. Highly methylated cytosine residues of CpG and CpWpG (W contains A or T) sites were distinctively detected in the promoter and 5' coding regions of the transgenes 35S-bar and 35S-GtMADS in all gentian lines analysed. These lines also exhibited various degrees of cytosine methylation in asymmetrical sequences. The methylation frequencies in the other transgene, nopaline synthase (NOS) promoter-driven nptII, and the endogenous GtMADS gene coding region, were much lower and were variable compared with those in the 35S promoter regions. Transgene methylation was observed in the bialaphos-selected transgenic calluses expressing the transgenes, and methylation sequences were distributed preferentially around the as-1 element in the 35S promoter. Calluses derived from leaf tissues of silenced transgenic gentian also exhibited transgene suppression, but expression was recovered by treatment with the methylation inhibitor 5-aza-2'-deoxycytidine (aza-dC). These results indicated that cytosine methylation occurs exclusively in the 35S promoter regions of the expressed transgenes during selection of gentian transformants, causing transcriptional gene silencing.

Functions of two genes in aluminium (Al) stress resistance: repression of oxidative damage by the AtBCB gene and promotion of efflux of Al ions by the NtGDI1gene

The functions of two genes whose expression provides tolerance to aluminium (Al) stress were investigated using plants and Saccharomyces cerevisiae (yeast): the Arabidopsis thaliana blue copper binding gene (AtBCB) and Nicotiana tabacum guanosine diphosphate (GDP) dissociation inhibitor gene (NtGDI1). To determine the localization of these proteins, each gene was fused to the green fluorescent protein (GFP) gene and introduced into onion epidermal cells. AtBCB was localized to cell membrane region and NtGDI1 to cytoplasm. Transgenic lines over-expressing the AtBCB gene showed constitutive lignin production in whole roots. By contrast, wild-type Arabidopsis (Ler) produced a negligible level of lignin and enhanced lignin production in the root-tip region by Al stress. Compared with Ler, the AtBCB-expressing lines showed a lower deposition of malon dialdehyde after Al stress. Microscopic observation of the Al-treated roots indicated that the deposition of lipid peroxides was clearly low in the area where lignin accumulated. It was proposed that lipid peroxidation caused by Al stress was diminished by the formation of lignin. Expression of the NtGDI1 gene in yeast complemented the temperature-sensitive phenotype of a sec19 mutant at 37 degrees C. This gene also complemented an Al-sensitive phenotype shown by the sec19 mutant at the permissive temperature of 32 degrees C. These results suggested that the yeast Sec19 vesicle transport system has a function in providing basal Al resistance in yeast by the export of Al ions. It was also proposed that over-expression of the NtGDI1 protein activates an Al efflux system that protects Arabidopsis against Al toxicity.

Suppression of root nodule formation by artificial expression of the TrEnodDR1 (coat protein of White clover cryptic virus 1) gene in Lotus japonicus

TrEnodDR1 (Trifolium repens early nodulin downregulation 1) encodes a coat protein of White clover cryptic virus 1. Its expression in white clover was down-regulated at the time when root nodules formed. We surmised that its artificial expression would interfere with root nodulation. Therefore, we investigated the effects of its artificial expression on the growth and root nodulation of Lotus japonicus (a model legume). Transformants were prepared by Agrobacterium spp.-mediated transformation. The growth of transformants was reduced and the number of root nodules per unit root length was greatly decreased relative to control. The concentration of endogenous abscisic acid (ABA), which controls nodulation, increased in plants containing TrEnodDR1. These phenotypes clearly were canceled by treatment with abamine, a specific inhibitor of ABA biosynthesis. The increase in endogenous ABA concentration explained the reduced stomatal aperture and the deformation of root hairs in response to inoculation of transgenic L. japonicus with Mesorhizobium loti. Transcriptome comparison between TrEnodDR1 transformants and control plants showed clearly enhanced expression levels of various defense response genes in transformants. These findings suggest that TrEnodDR1 suppresses nodulation by increasing the endogenous ABA concentration, perhaps by activating the plant's innate immune response. This is the first report of the suppression of nodulation by the artificial expression of a virus coat protein gene.

Metabolic engineering of proanthocyanidins by ectopic expression of transcription factors in Arabidopsis thaliana

Genetic transformation of Arabidopsis thaliana with the Arabidopsis TT2 MYB transcription factor resulted in ectopic expression of the BANYULS gene, encoding anthocyanidin reductase, AHA10 encoding a P-type proton-pump and TT12 encoding a transporter involved in proanthocyanidin biosynthesis. When coupled with constitutive expression of PAP1, a positive regulator of anthocyanin biosynthesis, TT2 expression in Arabidopsis led to accumulation of proanthocyanidins, but only in a subset of cells in which the BANYULS promoter is naturally expressed. Ectopic expression of the maize Lc MYC transcription factor weakly induced AHA10 but did not induce BANYULS, TT12 or accumulation of proanthocyanidins. However, high-level combined expression of TT2, PAP1 and Lc resulted in proanthocyanidin synthesis throughout young leaves and cotyledons, followed by death of the plants 1 to 2 weeks after germination. We discuss these results in relation to engineering proanthocyanidins to improve the quality of food and forage plants.

Molecular characterization of a cold-induced plasma membrane protein gene from wheat

As a means to study the function of plasma membrane proteins during cold acclimation, we have isolated a cDNA clone for wpi6 which encodes a putative plasma membrane protein from cold-acclimated winter wheat. The wpi6 gene encodes a putative 5.9 kDa polypeptide with two predicted membrane-spanning domains, the sequence of which shows high sequence similarity with BLT101-family proteins from plants and yeast. Strong induction of wpi6 mRNA was observed during an early stage of cold acclimation in root and shoot tissues of both winter and spring wheat cultivars. In contrast to blt101 in barley, wpi6 mRNA was also induced by drought and salinity stresses, and exogenous application of ABA. Expression of wpi6 in a Deltapmp3 mutant of Saccharomyces cerevisiae, which is disturbed in plasma membrane potential due to the lack of a BLT101-family protein, partially complemented NaCl sensitivity of the mutant. Transient expression analysis of a WPI6::GFP fusion protein in onion epidermal cells revealed that WPI6 is localized in the plasma membrane. Taken together, these data suggested that WPI6 may have a protective role in maintaining plasma membrane function during cold acclimation in wheat.

Tetrahydrocannabinolic acid synthase, the enzyme controlling marijuana psychoactivity, is secreted into the storage cavity of the glandular trichomes

Tetrahydrocannabinolic acid (THCA) synthase is the enzyme responsible for the production of tetrahydrocannabinol (THC), the psychoactive component of marijuana (Cannabis sativa L.). We suggest herein that THCA is biosynthesized in the storage cavity of the glandular trichomes based on the following observations. (i) The exclusive expression of THCA synthase was confirmed in the secretory cells of glandular trichomes by reverse transcription-PCR (RT-PCR) analysis. (ii) THCA synthase activity was detected in the storage cavity content. (iii) Transgenic tobacco expressing THCA synthase fused to green fluorescent protein showed fluorescence in the trichome head corresponding to the storage cavity. These results also showed that secretory cells of the glandular trichomes secrete not only metabolites but also biosynthetic enzyme.

Mammalian Bax initiates plant cell death through organelle destruction

Mammalian Bax is known to cause cell death when expressed in plants. We examined transgenic plants expressing both Bax and organelle-targeted green fluorescent protein to determine the cellular changes that occur during Bax-induced cell death. The mitochondria changed morphologically from being bacilli-shaped to being round, eventually becoming swollen. Mitochondria streaming also stopped. The chloroplasts lost membrane function and their contents leaked out, followed by the disruption of the vacuole. Light was not essential for Bax-induced ion leakage or organelle disruption. These results indicate that Bax induces temporal and spatial cell death events at the organelle level in the plant. A heterologous system, using Bax, would therefore be available to investigate cell death, which is commonly conserved in animals and plants.

An auxilin-like J-domain protein, JAC1, regulates phototropin-mediated chloroplast movement in Arabidopsis

The ambient-light conditions mediate chloroplast relocation in plant cells. Under the low-light conditions, chloroplasts accumulate in the light (accumulation response), while under the high-light conditions, they avoid the light (avoidance response). In Arabidopsis (Arabidopsis thaliana), the accumulation response is mediated by two blue-light receptors, termed phototropins (phot1 and phot2) that act redundantly, and the avoidance response is mediated by phot2 alone. A mutant, J-domain protein required for chloroplast accumulation response 1 (jac1), lacks the accumulation response under weak blue light but shows a normal avoidance response under strong blue light. In dark-adapted wild-type cells, chloroplasts accumulate on the bottom of cells. Both the jac1 and phot2 mutants are defective in this chloroplast movement in darkness. Positional cloning of JAC1 reveals that this gene encodes a J-domain protein, resembling clathrin-uncoating factor auxilin at its C terminus. The amounts of JAC1 transcripts and JAC1 proteins are not regulated by light and by phototropins. A green fluorescent protein-JAC1 fusion protein showed a similar localization pattern to green fluorescent protein alone in a transient expression assay using Arabidopsis mesophyll cells and onion (Allium cepa) epidermal cells, suggesting that the JAC1 protein may be a soluble cytosolic protein. Together, these results suggest that JAC1 is an essential component of phototropin-mediated chloroplast movement.

Organization and metabolism of plastids and mitochondria in arbuscular mycorrhizal roots of Medicago truncatula

Colonization of root cortical cells by arbuscular mycorrhizal fungi leads to marked cytological changes of plastids and mitochondria. Plastids in particular are forming tubular extensions partially connecting individual organelles in a network-like way. These cytological changes correspond to an increased need for plastid and mitochondrial products during establishment and functioning of the symbiosis. The analysis of metabolite and transcript levels in mycorrhizal and nonmycorrhizal roots from Medicago truncatula revealed concomitant changes regarding a number of metabolic pathways. Our results indicate the activation of the mitochondrial tricarboxylic acid cycle and of plastid biosynthetic pathways producing fatty acids, amino acids, and apocarotenoids. These observations provide a general overview of structural and metabolic changes of plastids and mitochondria during colonization of root cortical cells by arbuscular mycorrhizal fungi.

Up-regulation of OsBIHD1, a rice gene encoding BELL homeodomain transcriptional factor, in disease resistance responses

In the present study, we cloned and identified a full-length cDNA of a rice gene, OsBIHD1, encoding a homeodomain type transcriptional factor. OsBIHD1 is predicted to encode a 642 amino acid protein and the deduced protein sequence of OsBIHD1 contains all conserved domains, a homeodomain, a BELL domain, a SKY box, and a VSLTLGL box, which are characteristics of the BELL type homedomain proteins. The recombinant OsBIHD1 protein expressed in Escherichia coli bound to the TGTCA motif that is the characteristic cis-element DNA sequence of the homeodomain transcriptional factors. Subcellular localization analysis revealed that the OsBIHD1 protein localized in the nucleus of the plant cells. The OsBIHD1 gene was mapped to chromosome 3 of the rice genome and is a single-copy gene with four exons and three introns. Northern blot analysis showed that expression of OsBIHD1 was activated upon treatment with benzothiadiazole (BTH), which is capable of inducing disease resistance. Expression of OsBIHD1 was also up-regulated rapidly during the first 6 h after inoculation with Magnaporthe grisea in BTH-treated rice seedlings and during the incompatible interaction between M. grisea and a resistant genotype. These results suggest that OsBIHD1 is a BELL type of homeodomain transcription factor present in the nucleus, whose induction is associated with resistance response in rice.

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.

PHYTOCLOCK 1 encoding a novel GARP protein essential for the Arabidopsis circadian clock

Previously, we screened 50 000 seedlings of Arabidopsis thaliana carrying a P(GI)::LUC+ bioluminescence reporter gene mutagenized with ethylmethanesulfonate for mutants with phenotypes of extensively altered circadian rhythms, and identified three loci, PHYTOCLOCK 1 (PCL1), PCL2 and PCL3, whose mutations cause arrhythmia. Here we succeeded to clone the PCL1 gene and show that the PCL1 gene encodes a novel DNA binding protein belonging to the GARP protein family and is essential for a functional clock oscillator in A. thaliana. The PCL1 gene satisfies the requirements for the clock oscillator gene: (i) pcl1 null mutations caused arrhythmia in multiple circadian outputs, including expression of potential clock genes TOC1, CCA1 and LHY, and flowering lacked a photoperiodic response; (ii) PCL1 expression showed circadian rhythm in both constant light and constant dark; (iii) over-expression of the PCL1 gene gradually caused arrhythmicity in all the multiple circadian outputs examined; and (iv) the PCL1 gene controlled its own expression via negative feedback. Therefore, the PCL1 gene is the clock oscillator gene essential to the generation of clock oscillation in the higher plant.

Effects of calreticulin on viral cell-to-cell movement

Cell-to-cell tobacco mosaic virus movement protein (TMV MP) mediates viral spread between the host cells through plasmodesmata. Although several host factors have been shown to interact with TMV MP, none of them coresides with TMV MP within plasmodesmata. We used affinity purification to isolate a tobacco protein that binds TMV MP and identified it as calreticulin. The interaction between TMV MP and calreticulin was confirmed in vivo and in vitro, and both proteins were shown to share a similar pattern of subcellular localization to plasmodesmata. Elevation of the intracellular levels of calreticulin severely interfered with plasmodesmal targeting of TMV MP, which, instead, was redirected to the microtubular network. Furthermore, in TMV-infected plant tissues overexpressing calreticulin, the inability of TMV MP to reach plasmodesmata substantially impaired cell-to-cell movement of the virus. Collectively, these observations suggest a functional relationship between calreticulin, TMV MP, and viral cell-to-cell movement.

Measles virus superinfection immunity and receptor redistribution in persistently infected NT2 cells

A recombinant measles virus (MV) expressing red fluorescent protein (MVDsRed1) was used to produce a persistently infected cell line (piNT2-MVDsRed1) from human neural precursor (NT2) cells. A similar cell line (piNT2-MVeGFP) was generated using a virus that expresses enhanced green fluorescent protein. Intracytoplasmic inclusions containing the viral nucleocapsid protein were evident in all cells and viral glycoproteins were present at the cell surface. Nevertheless, the cells did not release infectious virus nor did they fuse to generate syncytia. Uninfected NT2 cells express the MV receptor CD46 uniformly over their surface, whereas CD46 was present in cell surface aggregates in the piNT2 cells. There was no decrease in the overall amount of CD46 in piNT2 compared to NT2 cells. Cell-to-cell fusion was observed when piNT2 cells were overlaid onto confluent monolayers of MV receptor-positive cells, indicating that the viral glycoproteins were correctly folded and processed. Infectious virus was released from the underlying cells, indicating that persistence was not due to gross mutations in the virus genome. Persistently infected cells were superinfected with MV or canine distemper virus and cytopathic effects were not observed. However, mumps virus could readily infect the cells, indicating that superinfection immunity is not caused by general soluble antiviral factors. As MVeGFP and MVDsRed1 are antigenically indistinguishable but phenotypically distinct it was possible to use them to measure the degree of superinfection immunity in the absence of any cytopathic effect. Only small numbers of non-fusing green fluorescent piNT2-MVDsRed1 cells (1 : 300 000) were identified in which superinfecting MVeGFP entered, replicated and expressed its genes.

Mitochondrial behaviour in the early stages of ROS stress leading to cell death in Arabidopsis thaliana

BACKGROUND AND AIMS

Reactive oxygen species (ROS) are involved in triggering cell death. To visualize mitochondrial behaviour under ROS stress, transgenic arabidopsis plants possessing mitochondrial-targeted GFP (S65T) were studied.

METHODS

Arabidopsis leaves were treated with ROS and ROS-inducing chemicals such as hydrogen peroxide, paraquat and menadione. Microscopic observations were carried out using a confocal laser scanning microscope system, and electrolyte leakage was also monitored.

KEY RESULTS

After treatment, mitochondria showed morphological changes from a bacillus-like to a round shape. The size of mitochondria treated with H(2)O(2) decreased by half compared with controls. Concurrently, cytoplasmic streaming was blocked and mitochondria eventually swelled. Treatment of leaves with butanedione monoxime, an inhibitor of myosin ATPase, resulted in similar behaviour of mitochondria to that under ROS stress.

CONCLUSIONS

The results indicate that morphological changes of mitochondria and cessation of cytoplasmic streaming may interact, and this phenomenon is one of the features of ROS stress-induced cell death.

Agrobacterium tumefaciens increases cytokinin production in plastids by modifying the biosynthetic pathway in the host plant

Agrobacterium tumefaciens infects plants and induces the formation of tumors called "crown galls" by integrating the transferred-DNA (T-DNA) region of the Ti-plasmid into the plant nuclear genome. Tumors are formed because the T-DNA encodes enzymes that modify the synthesis of two plant growth hormones, auxin and cytokinin (CK). Here, we show that a CK biosynthesis enzyme, Tmr, which is encoded by the Agrobacterium T-DNA region, is targeted to and functions in plastids of infected plant cells, despite having no typical plastid-targeting sequence. Evidence is provided that Tmr is an adenosine phosphate-isopentenyltransferase (IPT) that creates a new CK biosynthesis bypass by using 1-hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate (HMBDP) as a substrate. Unlike in the conventional CK biosynthesis pathway in plants, trans-zeatin-type CKs are produced directly without the requirement for P450 monooxygenase-mediated hydroxylation. Consistent with the plastid localization of Tmr, HMBDP is an intermediate in the methylerythritol phosphate pathway, a plastid-localized biosynthesis route for universal isoprenoid precursors. These results demonstrate that A. tumefaciens modifies CK biosynthesis by sending a key enzyme into plastids of the host plant to promote tumorigenesis.

Functional analysis of Arabidopsis ethylene-responsive element binding protein conferring resistance to Bax and abiotic stress-induced plant cell death

Arabidopsis (Arabidopsis thaliana) ethylene-responsive element binding protein (AtEBP) gene was isolated as a suppressor of Bax-induced cell death by functional screening in yeast (Saccharomyces cerevisiae). To further examine the cell death suppressive action of AtEBP in plant cells, we established transgenic tobacco (Nicotiana tabacum) plants overexpressing AtEBP as well as transgenic tobacco plants ectopically expressing mouse Bax protein under a dexamethasone-inducible promoter. We prepared the crosses of the selective lines of each transgenic plant, which were evaluated in terms of cell death suppression activity. Results indicate that AtEBP suppressed Bax-induced cell death in tobacco plants, an action also associated with a lowered level of ion leakage. Furthermore, tobacco Bright Yellow-2 cells overexpressing AtEBP conferred resistance to hydrogen peroxide (H(2)O(2)) and heat treatments. AtEBP protein localized in the nucleus and functioned as an in vivo transcription activator as confirmed in transient assays and experiments using stable transgenic system. Up-regulation of defense genes was observed in transgenic Arabidopsis plants overexpressing AtEBP. Based on the analysis of mRNA accumulation in ethylene-related mutants, the position of AtEBP in signaling pathway is presented.

Involvement of alpha-amylase I-1 in starch degradation in rice chloroplasts

To determine the role of alpha-amylase isoform I-1 in the degradation of starch in rice leaf chloroplasts, we generated a series of transgenic rice plants with suppressed expression or overexpression of alpha-amylase I-1. In the lines with suppressed expression of alpha-amylase I-1 at both the mRNA and protein levels, seed germination and seedling growth were markedly delayed in comparison with those in the wild-type plants. However, the growth retardation was overcome by supplementation of sugars. Interestingly, a significant increase of starch accumulation in the young leaf tissues was observed under a sugar-supplemented condition. In contrast, the starch content of leaves was reduced in the plants overexpressing alpha-amylase I-1. In immunocytochemical analysis with specific anti-alpha-amylase I-1 antiserum, immuno-gold particles deposited in the chloroplasts and extracellular space in young leaf cells. We further examined the expression and targeting of alpha-amylase I-1 fused with the green fluorescent protein in re-differentiated green cells, and showed that the fluorescence of the expressed fusion protein co-localized with the chlorophyll autofluorescence in the transgenic cells. In addition, mature protein species of alpha-amylase I-1 bearing an oligosaccharide side chain were detected in the isolated chloroplasts. Based on these results, we concluded that alpha-amylase I-1 targets the chloroplasts through the endoplasmic reticulum-Golgi system and plays a significant role in the starch degradation in rice leaves.

Visualization of plastid nucleoids in situ using the PEND-GFP fusion protein

Plastid DNA is a circular molecule of 120-150 kbp, which is organized into a protein-DNA complex called a nucleoid. Although various plastids other than chloroplasts exist, such as etioplasts, amyloplasts and chromoplasts, it is not easy to observe plastid nucleoids within the cells of many non-green tissues. The PEND (plastid envelope DNA-binding) protein is a DNA-binding protein in the inner envelope membrane of developing chloroplasts, and a DNA-binding domain called cbZIP is present at its N-terminus. We made various PEND-green fluorescent protein (GFP) fusion proteins using the cbZIP domains from various plants, and found that they were localized in the chloroplast nucleoids in transient expression in leaf protoplasts. In stable transformants of Arabidopsis thaliana, PEND-GFP fusion proteins were also localized in the nucleoids of various plastids. We have succeeded in visualizing plastid nucleoids in various intact tissues using this stable transformant. This technique is useful in root, flower and pollen, in which it had been difficult to observe plastid nucleoids. The relative arrangement of nucleoids within a chloroplast was kept unchanged when the chloroplast moved within a cell. During the division of plastid, nucleoids formed a network structure, which made possible equal partition of nucleoids.

Identification of an Arabidopsis thaliana gene for cardiolipin synthase located in mitochondria

Cardiolipin (CL) is an anionic phospholipid with a dimeric structure. In eukaryotes, it is primarily localized in the inner membranes of mitochondria. Although the biosynthetic pathway of CL is well known, the gene for CL synthase has not been identified in any higher organisms. In this study, the CLS gene for a CL synthase has been identified in a higher plant, Arabidopsis thaliana. We have shown that the CLS gene encodes a CL synthase by demonstrating its ability to catalyze the reaction of CL synthesis from CDP-diacylglycerol and phosphatidylglycerol, and that CLS is targeted into mitochondria. These findings demonstrate that CLS is a CL synthase located in mitochondria.