FUS immunoreactivity of neuronal and glial intranuclear inclusions in intranuclear inclusion body disease

AIMS

Recent studies have shown that fused-in-sarcoma (FUS) protein is a component of 'neuronal' intranuclear inclusion bodies (INIBs) in the brains of patients with intranuclear inclusion body disease (INIBD). However, the extent and frequency of FUS-immunoreactive structures in INIBD are uncertain.

METHODS

We immunohistochemically examined the brain, spinal cord and peripheral ganglia from five patients with INIBD and five control subjects, using anti-FUS antibodies.

RESULTS

In controls, the nuclei of both neurones and glial cells were intensely immunolabelled with anti-FUS and neuronal cytoplasm was weakly positive for FUS. In INIBD, neuronal and glial INIBs in the brain and spinal cord were positive for FUS. FUS-positive INIBs were also found in the peripheral ganglia. The proportion of FUS-positive neuronal INIBs relative to the total number of inclusion-bearing neurones ranged from 55.6% to 83.3% (average 73.2%) and that of FUS-positive glial INIBs ranged from 45.9% to 85.7% (average 62.7%). The nucleus and cytoplasm of inclusion-bearing neurones and glial cells showed no FUS immunoreactivity.

CONCLUSIONS

These findings suggest that FUS is incorporated into INIBs in both neurones and glial cells and that loss of normal FUS immunoreactivity may result from reduced protein expression and/or sequestration within inclusions.

Gynogenesis in gentians (Gentiana triflora, G. scabra): production of haploids and doubled haploids

Gynogenesis was investigated on gentian (Gentiana triflora, G. scabra and their hybrids), which is an important ornamental flower. When unfertilized ovules were cultured in 1/2 NLN medium containing a high concentration of sucrose (100 g/l), embryo-like structures (ELS) were induced. Although genotypic variation was observed in ELS induction, all four genotypes produced ELSs ranging from 0.93 to 0.04 ELSs per flower bud. The ovules collected from flower buds of later stages (just before anthesis or flower anthesis) tended to exhibit higher response. The dark culture condition produced more than four times as many ELSs than in 16-h light condition. A significant number of plantlets were directly regenerated from ELSs on MS regeneration medium. The ploidy levels of 179 regenerated plants were determined by flow cytometry, revealing that the majority of them were diploid (55.9%) and haploid (31.3%). When a total of 54 diploid plants were examined by molecular genetic markers, 52 (96.3%) were considered as doubled haploids (DHs). This is the first report showing successful gynogenesis in gentian. The production of haploids and DHs by unfertilized ovule culture opens a novel prospect in gentian F1 hybrid breeding.

Phytochrome B regulates Heading date 1 (Hd1)-mediated expression of rice florigen Hd3a and critical day length in rice

Many plants require circadian clock and light information for the photoperiodic control of flowering. In Arabidopsis, a long-day plant (LDP), flowering is triggered by the circadian clock-controlled expression of CONSTANS (CO) and light stabilization of the CO protein to induce FT (FLOWERING LOCUS T). In rice, a short-day plant (SDP), the CO ortholog Heading date 1 (Hd1) regulates FT ortholog Hd3a, but regulation of Hd3a by Hd1 differs from that in Arabidopsis. Here, we report that phytochrome B (phyB)-mediated suppression of Hd3a is a primary cause of long-day suppression of flowering in rice, based on the three complementary discoveries. First, overexpression of Hd1 causes a delay in flowering under SD conditions and this effect requires phyB, suggesting that light modulates Hd1 control of Hd3a transcription. Second, a single extension of day length decreases Hd3a expression proportionately with the length of daylight. Third, Hd1 protein levels in Hd1-overexpressing plants are not altered in the presence of light. These results also suggest that phyB-mediated suppression of Hd3a expression is a component of the molecular mechanism for critical day length in rice.

Arabidopsis EMBRYOMAKER encoding an AP2 domain transcription factor plays a key role in developmental change from vegetative to embryonic phase

Although several types of plant cells retain the competence to enter into embryonic development without fertilization, the molecular mechanism(s) underlying ectopic embryogenesis is largely unknown. To gain insight into this mechanism, in a previous study we identified 136 ESTs specifically expressed in microspore embryogenesis of Brassica napus. Here, we describe the characterization of the Arabidopsis EMBRYOMAKER (EMK) gene, which is homologous to one of the identified Brassica ESTs (BnGemb-58) and encodes an AP2 domain transcription factor. The AtEMK was expressed in developing and mature embryos, but its rapid disappearance occurred during germination. After germination, the expression of AtEMK was found in the root apical meristem and the distal parts of cotyledons. Although a mutant lacking AtEMK exhibited no distinctive defects in the embryo, ectopic expression of AtEMK induced embryo-like structures from cotyledons. The embryo-like structures contained high concentration of lipids, expressed several embryo-specific genes, and could convert into independent plants, indicating that the structures are somatic embryos. In vitro culture, AtEMK enhanced the efficiency of somatic embryogenesis. Furthermore, ectopic expression of AtEMK caused the formation of trichomes on cotyledons, dedifferentiated several tissues into calli, and retarded root development, demonstrating that AtEMK is harmful for the normal development of plants after germination. From these results, we conclude that the AtEMK is a key player to maintain embryonic identity, and the rapid disappearance of AtEMK expression during germination is essential for the developmental transition between the embryonic and vegetative phases in plants.

A gene network for long-day flowering activates RFT1 encoding a mobile flowering signal in rice

Although some genes that encode sensory or regulatory elements for photoperiodic flowering are conserved between the long-day (LD) plant Arabidopsis thaliana and the short-day (SD) plant rice, the gene networks that control rice flowering, and particularly flowering under LD conditions, are not well understood. We show here that RICE FLOWERING LOCUS T 1 (RFT1), the closest homolog to Heading date 3a (Hd3a), is a major floral activator under LD conditions. An RFT1:GFP fusion protein localized in the shoot apical meristem (SAM) under LD conditions, suggesting that RFT1 is a florigen gene in rice. Furthermore, mutants in OsMADS50, a rice ortholog of Arabidopsis SUPPRESOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1) did not flower up to 300 days after sowing under LD conditions, indicating that OsMADS50, which acts upstream of RFT1, promotes flowering under LD conditions. We propose that both positive (OsMADS50 and Ehd1) and negative (Hd1, phyB and Ghd7) regulators of RFT1 form a gene network that regulates LD flowering in rice. Among these regulators, Ehd1, a rice-specific floral inducer, integrates multiple pathways to regulate RFT1, leading to flowering under appropriate photoperiod conditions. A rice ortholog of Arabidopsis APETALA1, OsMADS14, was expressed in the floral meristem in wild-type but not in RFT1 RNAi plants, suggesting that OsMADS14 is activated by RFT1 protein in the SAM after the transition to flowering. We have thus exposed a network of genes that regulate LD flowering in rice.

Hd3a and RFT1 are essential for flowering in rice

RICE FLOWERING LOCUS T 1 (RFT1/FT-L3) is the closest homologue of Heading date 3a (Hd3a), which is thought to encode a mobile flowering signal and promote floral transition under short-day (SD) conditions. RFT1 is located only 11.5 kb from Hd3a on chromosome 6. Although RFT1 RNAi plants flowered normally, double RFT1-Hd3a RNAi plants did not flower up to 300 days after sowing (DAS), indicating that Hd3a and RFT1 are essential for flowering in rice. RFT1 expression was very low in wild-type plants, but there was a marked increase in RFT1 expression by 70 DAS in Hd3a RNAi plants, which flowered 90 DAS. H3K9 acetylation around the transcription initiation site of the RFT1 locus had increased by 70 DAS but not at 35 DAS. In the absence of Hd3a and RFT1 expression, transcription of OsMADS14 and OsMADS15, two rice orthologues of Arabidopsis APETALA1, was strongly reduced, suggesting that they act downstream of Hd3a and RFT1. These results indicate that Hd3a and RFT1 act as floral activators under SD conditions, and that RFT1 expression is partly regulated by chromatin modification.

Identification of dynamin as an interactor of rice GIGANTEA by tandem affinity purification (TAP)

GIGANTEA (GI), CONSTANS (CO) and FLOWERING LOCUS T (FT) regulate photoperiodic flowering in Arabidopsis. In rice, OsGI, Hd1 and Hd3a were identified as orthologs of GI, CO and FT, respectively, and are also important regulators of flowering. Although GI has roles in both flowering and the circadian clock, our understanding of its biochemical functions is still limited. In this study, we purified novel OsGI-interacting proteins by using the tandem affinity purification (TAP) method. The TAP method has been used effectively in a number of model species to isolate proteins that interact with proteins of interest. However, in plants, the TAP method has been used in only a few studies, and no novel proteins have previously been isolated by this method. We generated transgenic rice plants and cell cultures expressing a TAP-tagged version of OsGI. After a two-step purification procedure, the interacting proteins were analyzed by mass spectrometry. Seven proteins, including dynamin, were identified as OsGI-interacting proteins. The interaction of OsGI with dynamin was verified by co-immunoprecipitation using a myc-tagged version of OsGI. Moreover, an analysis of Arabidopsis dynamin mutants indicated that although the flowering times of the mutants were not different from those of wild-type plants, an aerial rosette phenotype was observed in the mutants. We also found that OsGI is present in both the nucleus and the cytosol by Western blot analysis and by transient assays. These results indicate that the TAP method is effective for the isolation of novel proteins that interact with target proteins in plants.

Hd3a protein is a mobile flowering signal in rice

Florigen, the mobile signal that moves from an induced leaf to the shoot apex and causes flowering, has eluded identification since it was first proposed 70 years ago. Understanding the nature of the mobile flowering signal would provide a key insight into the molecular mechanism of floral induction. Recent studies suggest that the Arabidopsis FLOWERING LOCUS T (FT) gene is a candidate for encoding florigen. We show that the protein encoded by Hd3a, a rice ortholog of FT, moves from the leaf to the shoot apical meristem and induces flowering in rice. These results suggest that the Hd3a protein may be the rice florigen.

Suppression of the floral activator Hd3a is the principal cause of the night break effect in rice

A short exposure to light in the middle of the night causes inhibition of flowering in short-day plants. This phenomenon is called night break (NB) and has been used extensively as a tool to study the photoperiodic control of flowering for many years. However, at the molecular level, very little is known about this phenomenon. In rice (Oryza sativa), 10 min of light exposure in the middle of a 14-h night caused a clear delay in flowering. A single NB strongly suppressed the mRNA of Hd3a, a homolog of Arabidopsis thaliana FLOWERING LOCUS T (FT), whereas the mRNAs of OsGI and Hd1 were not affected. The NB effect on Hd3a mRNA was maximal in the middle of the 14-h night. The phyB mutation abolished the NB effect on flowering and Hd3a mRNA, indicating that the NB effect was mediated by phytochrome B. Because expression of the other FT-like genes was very low and not appreciably affected by NB, our results strongly suggest that the suppression of Hd3a mRNA is the principal cause of the NB effect on flowering in rice.

Suppression of the floral activator Hd3a is the principal cause of the night break effect in rice

A short exposure to light in the middle of the night causes inhibition of flowering in short-day plants. This phenomenon is called night break (NB) and has been used extensively as a tool to study the photoperiodic control of flowering for many years. However, at the molecular level, very little is known about this phenomenon. In rice (Oryza sativa), 10 min of light exposure in the middle of a 14-h night caused a clear delay in flowering. A single NB strongly suppressed the mRNA of Hd3a, a homolog of Arabidopsis thaliana FLOWERING LOCUS T (FT), whereas the mRNAs of OsGI and Hd1 were not affected. The NB effect on Hd3a mRNA was maximal in the middle of the 14-h night. The phyB mutation abolished the NB effect on flowering and Hd3a mRNA, indicating that the NB effect was mediated by phytochrome B. Because expression of the other FT-like genes was very low and not appreciably affected by NB, our results strongly suggest that the suppression of Hd3a mRNA is the principal cause of the NB effect on flowering in rice.

The Arabidopsis SUMO E3 ligase SIZ1 controls phosphate deficiency responses

Plants sense phosphate (Pi) deficiency and initiate signaling that controls adaptive responses necessary for Pi acquisition. Herein, evidence establishes that AtSIZ1 is a plant small ubiquitin-like modifier (SUMO) E3 ligase and is a focal controller of Pi starvation-dependent responses. T-DNA insertional mutated alleles of AtSIZ1 (At5g60410) cause Arabidopsis to exhibit exaggerated prototypical Pi starvation responses, including cessation of primary root growth, extensive lateral root and root hair development, increase in root/shoot mass ratio, and greater anthocyanin accumulation, even though intracellular Pi levels in siz1 plants were similar to wild type. AtSIZ1 has SUMO E3 ligase activity in vitro, and immunoblot analysis revealed that the protein sumoylation profile is impaired in siz1 plants. AtSIZ1-GFP was localized to nuclear foci. Steadystate transcript abundances of Pi starvation-responsive genes AtPT2, AtPS2, and AtPS3 were moderate but clearly greater in siz1 seedlings than in wild type, where Pi is sufficient. Pi starvation induced the expression of these genes to the same extent in siz1 and wild-type seedlings. However, two other Pi starvation-responsive genes, AtIPS1 and AtRNS1, are induced more slowly in siz1 seedlings by Pi limitation. PHR1, a MYB transcriptional activator of AtIPS1 and AtRNS1, is an AtSIZ1 sumoylation target. These results indicate that AtSIZ1 is a SUMO E3 ligase and that sumoylation is a control mechanism that acts both negatively and positively on different Pi deficiency responses.

Assessment of utility of meiosis-associated promoters of lily for induction of germinal ds transposition in transgenic rice

In order to suppress the somatic excision of the Ds element and increase the independent transposition events of the Ac/Ds transposon tagging system in rice, we employed promoters of two meiosis-specific genes of lily, LIM10 and LIM18. The LIM10 promoter directed GUS expression specifically in anthers, with the LIM18 promoter doing the same in the anthers and somatic tissue. Both promoters induced independent germinal transposition with the frequency of approximately 1%. The LIM10 promoter, lacking induction of somatic transposition, is considered to be useful for improving transposon-tagging efficiencies in rice.

Adaptation of photoperiodic control pathways produces short-day flowering in rice

The photoperiodic control of flowering is one of the important developmental processes of plants because it is directly related to successful reproduction. Although the molecular genetic analysis of Arabidopsis thaliana, a long-day (LD) plant, has provided models to explain the control of flowering time in this species, very little is known about its molecular mechanisms for short-day (SD) plants. Here we show how the photoperiodic control of flowering is regulated in rice, a SD plant. Overexpression of OsGI, an orthologue of the Arabidopsis GIGANTEA (GI) gene in transgenic rice, caused late flowering under both SD and LD conditions. Expression of the rice orthologue of the Arabidopsis CONSTANS (CO) gene was increased in the transgenic rice, whereas expression of the rice orthologue of FLOWERING LOCUS T (FT) was suppressed. Our results indicate that three key regulatory genes for the photoperiodic control of flowering are conserved between Arabidopsis, a LD plant, and rice, a SD plant, but regulation of the FT gene by CO was reversed, resulting in the suppression of flowering in rice under LD conditions.

C-terminal domain phosphatase-like family members (AtCPLs) differentially regulate Arabidopsis thaliana abiotic stress signaling, growth, and development

Cold, hyperosmolarity, and abscisic acid (ABA) signaling induce RD29A expression, which is an indicator of the plant stress adaptation response. Two nonallelic Arabidopsis thaliana (ecotype C24) T-DNA insertional mutations, cpl1 and cpl3, were identified based on hyperinduction of RD29A expression that was monitored by using the luciferase (LUC) reporter gene (RD29ALUC) imaging system. Genetic linkage analysis and complementation data established that the recessive cpl1 and cpl3 mutations are caused by T-DNA insertions in AtCPL1 (Arabidopsis C-terminal domain phosphatase-like) and AtCPL3, respectively. Gel assays using recombinant AtCPL1 and AtCPL3 detected innate phosphatase activity like other members of the phylogenetically conserved family that dephosphorylate the C-terminal domain of RNA polymerase II (RNAP II). cpl1 mutation causes RD29ALUC hyperexpression and transcript accumulation in response to cold, ABA, and NaCl treatments, whereas the cpl3 mutation mediates hyperresponsiveness only to ABA. Northern analysis confirmed that LUC transcript accumulation also occurs in response to these stimuli. cpl1 plants accumulate biomass more rapidly and exhibit delayed flowering relative to wild type whereas cpl3 plants grow more slowly and flower earlier than wild-type plants. Hence AtCPL1 and AtCPL3 are negative regulators of stress responsive gene transcription and modulators of growth and development. These results suggest that C-terminal domain phosphatase regulation of RNAP II phosphorylation status is a focal control point of complex processes like plant stress responses and development. AtCPL family members apparently have both unique and overlapping transcriptional regulatory functions that differentiate the signal output that determines the plant response.

Differential expression and function of Arabidopsis thaliana NHX Na+/H+ antiporters in the salt stress response

The Arabidopsis thaliana vacuolar Na+/H+ antiporter AtNHX1 is a salt tolerance determinant. Predicted amino acid sequence similarity, protein topology and the presence of functional domains conserved in AtNHX1 and prototypical mammalian NHE Na+/H+ exchangers led to the identification of five additional AtNHX genes (AtNHX2-6). The AtNHX1 and AtNHX2 mRNAs are the most prevalent transcripts among this family of genes in seedling shoots and roots. A lower-abundance AtNHX5 mRNA is present in both shoots and roots, whereas AtNHX3 transcript is expressed predominantly in roots. AtNHX4 and AtNHX6 mRNAs were detected only by RT-PCR. AtNHX1, 2 or 5 suppress, with differential efficacy, the Na+/Li+-sensitive phenotype of a yeast mutant that is deficient in the endosomal/vacuolar Na+/H+ antiporter ScNHX1. Ion accumulation data indicate that these AtNHX proteins function to facilitate Na+ ion compartmentalization and maintain intracellular K+ status. Seedling steady-state mRNA levels of AtNHX1 and AtNHX2 increase similarly after treatment with NaCl, an equi-osmolar concentration of sorbitol, or ABA, whereas AtNHX5 transcript abundance increases only in response to salt treatment. Hyper-osmotic up-regulation of AtNHX1, 2 or 5 expression is not dependent on the SOS pathway that controls ion homeostasis. However, steady-state AtNHX1, 2 and 5 transcript abundance is greater in sos1, sos2 and sos3 plants growing in medium that is not supplemented with sorbitol or NaCl, providing evidence that transcription of these genes is negatively affected by the SOS pathway in the absence of stress. AtNHX1 and AtNHX2 transcripts accumulate in response to ABA but not to NaCl in the aba2-1, mutant indicating that the osmotic responsiveness of these genes is ABA-dependent. An as yet undefined stress signal pathway that is ABA- and SOS-independent apparently controls transcriptional up-regulation of AtNHX5 expression by hyper-saline shock. Similar to AtNHX1, AtNHX2 is localized to the tonoplast of plant cells. Together, these results implicate AtNHX2 and 5, together with AtNHX1, as salt tolerance determinants, and indicate that AtNHX2 has a major function in vacuolar compartmentalization of Na+.

AtHKT1 is a salt tolerance determinant that controls Na(+) entry into plant roots

Two Arabidopsis thaliana extragenic mutations that suppress NaCl hypersensitivity of the sos3-1 mutant were identified in a screen of a T-DNA insertion population in the genetic background of Col-0 gl1 sos3-1. Analysis of the genome sequence in the region flanking the T-DNA left border indicated that sos3-1 hkt1-1 and sos3-1 hkt1-2 plants have allelic mutations in AtHKT1. AtHKT1 mRNA is more abundant in roots than shoots of wild-type plants but is not detected in plants of either mutant, indicating that this gene is inactivated by the mutations. hkt1-1 and hkt1-2 mutations can suppress to an equivalent extent the Na(+) sensitivity of sos3-1 seedlings and reduce the intracellular accumulation of this cytotoxic ion. Moreover, sos3-1 hkt1-1 and sos3-1 hkt1-2 seedlings are able to maintain [K(+)](int) in medium supplemented with NaCl and exhibit a substantially higher intracellular ratio of K(+)/Na(+) than the sos3-1 mutant. Furthermore, the hkt1 mutations abrogate the growth inhibition of the sos3-1 mutant that is caused by K(+) deficiency on culture medium with low Ca(2+) (0.15 mM) and <200 microM K(+). Interestingly, the capacity of hkt1 mutations to suppress the Na(+) hypersensitivity of the sos3-1 mutant is reduced substantially when seedlings are grown in medium with low Ca(2+) (0.15 mM). These results indicate that AtHKT1 is a salt tolerance determinant that controls Na(+) entry and high affinity K(+) uptake. The hkt1 mutations have revealed the existence of another Na(+) influx system(s) whose activity is reduced by high [Ca(2+)](ext).

In vivo selection of Pseudomonas Aeruginosa with decreased susceptibilities to fluoroquinolones during fluoroquinolone treatment of urinary tract infection

OBJECTIVES

To present a case of fluoroquinolone treatment failure in urinary tract infection caused by Pseudomonas aeruginosa, accompanied by in vivo selection of the post-treatment isolate that showed decreased susceptibilities to fluoroquinolones, and to report fluoroquinolone resistance mechanisms in the post-treatment isolate.

METHODS

A patient with urinary tract infection was treated with a suboptimal dose of a fluorinated quinolone, gatifloxacin. P. aeruginosa strains were isolated before and after fluoroquinolone treatment. The pretreatment and post-treatment isolates were examined for relatedness by arbitrarily primed polymerase chain reaction. For these isolates, the minimum inhibitory concentration of antimicrobial agents was determined and mutations in the target genes (gyrA and parC) and regulatory genes (mexR and nfxB) for drug efflux pumps were analyzed.

RESULTS

Failure of fluoroquinolone treatment of urinary tract infection was observed. The post-treatment isolate, which was assumed to be isogenic to the pretreatment isolate, exhibited fourfold to 16-fold increases in the MIC of fluoroquinolones. In this isolate, a new mutation, not observed in the pretreatment isolate, was found only in the gyrA gene, resulting in an amino acid change of aspartic acid to asparagine in codon 87 of GyrA.

CONCLUSIONS

The P. aeruginosa isolate that was initially susceptible to fluoroquinolones showed decreased susceptibility to fluoroquinolones after treatment with a suboptimal dose of one fluoroquinolone. In the post-treatment isolate, the alteration of GyrA would be responsible for the decreased susceptibility to fluoroquinolones. We should be aware that inappropriate use of fluoroquinolones could select such a strain harboring a quinolone resistance-associated alteration of DNA gyrase.