A phenome-based functional analysis of transcription factors in the cereal head blight fungus, Fusarium graminearum

Fusarium graminearum is an important plant pathogen that causes head blight of major cereal crops. The fungus produces mycotoxins that are harmful to animal and human. In this study, a systematic analysis of 17 phenotypes of the mutants in 657 Fusarium graminearum genes encoding putative transcription factors (TFs) resulted in a database of over 11,000 phenotypes (phenome). This database provides comprehensive insights into how this cereal pathogen of global significance regulates traits important for growth, development, stress response, pathogenesis, and toxin production and how transcriptional regulations of these traits are interconnected. In-depth analysis of TFs involved in sexual development revealed that mutations causing defects in perithecia development frequently affect multiple other phenotypes, and the TFs associated with sexual development tend to be highly conserved in the fungal kingdom. Besides providing many new insights into understanding the function of F. graminearum TFs, this mutant library and phenome will be a valuable resource for characterizing the gene expression network in this fungus and serve as a reference for studying how different fungi have evolved to control various cellular processes at the transcriptional level.

Large collections of mutant lines allow for identification of gene functions. Here we constructed a mutant library of 657 putative transcription factors (TFs) through homologous recombination in the head blight fungus, Fusarium graminearum, providing a resource for understanding gene regulation in fungus. By screening these mutants in 17 phenotypic categories, we constructed a dataset of over 11,000 phenotypes. This study provides new insight into understanding multiple phenotypes caused by single TF as well as regulation of gene expression at the transcription level in F. graminearum. Furthermore, our TF mutant library will be a valuable resource for fungal studies through the distribution of mutants and easy access to our phenotypic and genetic data.

Altering sexual reproductive mode by interspecific exchange of MAT loci

Sexual fungi can be self-sterile (heterothallic, requiring genetically distinct partners) or self-fertile (homothallic, no partner required). In most ascomycetes, a single mating type locus (MAT) controls the ability to reproduce sexually. In the genus Cochliobolus, all heterothallic species have either MAT1-1 or MAT1-2 (but never both) in different individuals whereas all homothallic species carry both MAT1-1 and MAT1-2 in the same nucleus of an individual. It has been demonstrated, previously, that a MAT gene from homothallic Cochliobolus luttrellii can confer self-mating ability on a mat-deleted strain of its heterothallic relative, Cochliobolus heterostrophus. In this reciprocal study, we expressed, separately, the heterothallic C. heterostrophus MAT1-1-1 and MAT1-2-1 genes in a mat-deleted homothallic C. luttrellii strain and asked if this converts homothallic C. luttrellii to heterothallism. We report that: (1) A C. luttrellii transgenic strain carrying C. heterostrophus MAT1-1-1 and a C. luttrellii transgenic strain carrying C. heterostrophus MAT1-2-1 can mate in a heterothallic manner and the fertility of the cross is similar to that of a wild type C. luttrellii self. Full tetrads are always found. (2) A C. luttrellii transgenic strain carrying C. heterostrophus MAT1-1-1 can mate with the parental wild type C. luttrellii MAT1-1;MAT1-2 strain, indicating the latter is able to outcross, a result which was expected but has not been demonstrated previously. (3) A C. luttrellii transgenic strain carrying C. heterostrophus MAT1-2-1 cannot mate with the parental wild type C. luttrellii MAT1-1;MAT1-2 strain, indicating outcrossing specificity. (4) Each transgenic C. luttrellii strain, carrying only a single C. heterostrophus MAT gene, is able to self, although all pseudothecia produced are smaller than those of wild type and fertility is low (about 4-15% of the number of wild type asci). These data support the argument that in Cochliobolus spp., the primary determinant of reproductive mode is MAT itself, and that a heterothallic strain can be made homothallic or a homothallic strain can be made heterothallic by exchange of MAT genes. The selfing ability of transgenic C. luttrellii strains also suggests that both MAT1-1-1 and MAT1-2-1 genes of C. heterostrophus carry equivalent transcription regulatory activities, each capable of promoting sexual development when alone, in a suitable genetic background.

Histidine kinase two-component response regulator proteins regulate reproductive development, virulence, and stress responses of the fungal cereal pathogens Cochliobolus heterostrophus and Gibberella zeae

Histidine kinase (HK) phosphorelay signaling is a major mechanism by which fungi sense their environment. The maize pathogen Cochliobolus heterostrophus has 21 HK genes, 4 candidate response regulator (RR) genes (SSK1, SKN7, RIM15, REC1), and 1 gene (HPT1) encoding a histidine phosphotransfer domain protein. Because most HKs are expected to signal through RRs, these were chosen for deletion. Except for pigment and slight growth alterations for rim15 mutants, no measurable altered phenotypes were detected in rim15 or rec1 mutants. Ssk1p is required for virulence and affects fertility and proper timing of sexual development of heterothallic C. heterostrophus. Pseudothecia from crosses involving ssk1 mutants ooze masses of single ascospores, and tetrads cannot be found. Wild-type pseudothecia do not ooze. Ssk1p represses asexual spore proliferation during the sexual phase, and lack of it dampens asexual spore proliferation during vegetative growth, compared to that of the wild type. ssk1 mutants are heavily pigmented. Mutants lacking Skn7p do not display any of the above phenotypes; however, both ssk1 and skn7 mutants are hypersensitive to oxidative and osmotic stresses and ssk1 skn7 mutants are more exaggerated in their spore-type balance phenotype and more sensitive to stress than single mutants. ssk1 mutant phenotypes largely overlap hog1 mutant phenotypes, and in both types of mutant, the Hog1 target gene, MST1, is not induced. ssk1 and hog1 mutants were examined in the homothallic cereal pathogen Gibberella zeae, and pathogenic and reproductive phases of development regulated by Ssk1 and Hog1 were found to mirror, but also vary from, those of C. heterostrophus.

Xylogone ganodermophthora sp. nov., an ascomycetous pathogen causing yellow rot on cultivated mushroom Ganoderma lucidum in Korea

Yellow rot, caused by an ascomycetous fungus having a distinctive arthroconidial anamorph, is the most destructive disease of cultivated Ganoderma lucidum in Korea, but the identity of the yellow rot pathogen (YRP) remains uncertain. Isolates have been identified as Xylogone sphaerospora (with putative anamorph Sporendonema purpurascens) or as Arthrographis cuboidea. Therefore we used morphological features, pathogenicity tests and phylogenetic analyses of DNA sequences from the nuclear ribosomal genes, including partial small subunit and internal transcribed spacer regions, and from the gene encoding RNA polymerase second largest subunit to evaluate the relationship between YRP isolates and these species. YRP isolates formed a distinct subgroup within a clade that included X. sphaerospora, A. cuboidea and Scytalidium lignicola, the type species of Scytalidium, but the disposition of the clade within the Leotiomycetes was uncertain. We describe Xylogone ganodermophthora sp. nov. and Scytalidium ganodermophthorum sp. nov. for the teleomorph and anamorph of YRP respectively. Arthrographis cuboidea is reclassified as Scytalidium cuboideum comb. nov., and the anamorph of X. sphaerospora is named Scytalidium sphaerosporum sp. nov. In pathogenicity tests only X. ganodermophthora caused disease in Ganoderma lucidum. Amplified fragment length polymorphism analyses showed that X. ganodermophthora populations from diseased fruiting bodies or from oak wood in Korea consisted of two clonal groups.

Functional characterization and manipulation of the apicidin biosynthetic pathway in Fusarium semitectum

Apicidin is a cyclic tetrapeptide produced by certain isolates of Fusarium semitectum and has been shown to inhibit Apicomplexan histone deacetylase. An apicidin-producing strain (KCTC16676) of the filamentous fungus was mutated using an Agrobacterium tumefaciens-mediated transformation, resulting in 24 apicidin-deficient mutants. Three of the mutants had a T-DNA insertion in a gene that encodes a non-ribosomal peptide synthetase (NRPS). Results of sequence, expression, and gene deletion analyses defined an apicidin biosynthetic gene cluster, and the NRPS gene was named as apicidin synthetase gene 1 (APS1). A 63 kb region surrounding APS1 was sequenced and analysis revealed the presence of 19 genes. All of the genes including APS1 were individually deleted to determine their roles in apicidin biosynthesis. Chemical analyses of the mutant strains showed that eight genes are required for apicidin production and were used to propose an apicidin biosynthetic pathway. The apicidin analogues apicidin E, apicidin D(2) and apicidin B were identified from chemical analysis of the mutants. The cluster gene APS2, a putative transcription factor, was shown to regulate expression of the genes in the cluster and overexpression of APS2 increased apicidin production. This study establishes the apicidin biosynthetic pathway and provides new opportunities to improve the production of apicidin and produce new analogues.

In vivo high-resolution fluorescence microendoscopy for ovarian cancer detection and treatment monitoring

Background:

In patients with advanced ovarian cancer (OvCa), microscopic residual tumour nodules that remain after surgical debulking frequently escape detection by current treatment assessment methods and lead to disease recurrence. The aim of this study was to evaluate the use of high-resolution fibre-optic fluorescence imaging of the clinically approved photodynamic therapy (PDT) agent benzoporphyin-derivative monoacid ring A (BPD-MA) for detection of microscopic OvCa and for monitoring treatment response.

Methods:

Our fluorescence microendoscope consists of a flexible imaging fibre coupled to a custom epi-fluorescence system optimised for imaging BPD-MA, which, after a single administration, serves as both an imaging agent and a light-activated therapeutic agent. After characterisation in an in vitro OvCa 3D model, we used the flexible imaging fibre to minimally invasively image the peritoneal cavity of a disseminated OvCa murine model using BPD-MA administered intraperitoneally (i.p.). To evaluate longitudinal changes in response to treatment, we compared sets of images obtained before and after PDT with those from untreated mice imaged at the same time points.

Results:

By comparison with histopathology, we report an 86% sensitivity for tumour detection in vivo using the microendoscope. Using a custom routine to batch process-image data in the monitoring study, treated mice exhibited an average decrease of 58.8% in tumour volumes compared with an increase of 59.3% in untreated controls (P<0.05).

Conclusions:

Our findings indicate the potential of this approach as a reporter of treatment outcome that could aid in the rational design of strategies to mitigate recurrent OvCa.

Roles of the glyoxylate and methylcitrate cycles in sexual development and virulence in the cereal pathogen Gibberella zeae

The glyoxylate and methylcitrate cycles are involved in the metabolism of two- or three-carbon compounds in fungi. To elucidate the role(s) of these pathways in Gibberella zeae, which causes head blight in cereal crops, we focused on the functions of G. zeae orthologs (GzICL1 and GzMCL1) of the genes that encode isocitrate lyase (ICL) and methylisocitrate lyase (MCL), respectively, key enzymes in each cycle. The deletion of GzICL1 (DeltaGzICL1) caused defects in growth on acetate and in perithecium (sexual fruiting body) formation but not in virulence on barley and wheat, indicating that GzICL1 acts as the ICL of the glyoxylate cycle and is essential for self-fertility in G. zeae. In contrast, the DeltaGzMCL1 strains failed to grow on propionate but exhibited no major changes in other traits, suggesting that GzMCL1 is required for the methylcitrate cycle in G. zeae. Interestingly, double deletion of both GzICL1 and GzMCL1 caused significantly reduced virulence on host plants, indicating that both GzICL1 and GzMCL1 have redundant functions for plant infection in G. zeae. Thus, both GzICL1 and GzMCL1 may play important roles in determining major mycological and pathological traits of G. zeae by participating in different metabolic pathways for the use of fatty acids.

Local recurrence after curative resection in patients with colon and rectal cancers

BACKGROUND AND AIMS

There are a range of rates and a number of prognostic factors associated with the local recurrence of colorectal cancer after curative resection. The aim of this study was to identify the potential prognostic factors of local recurrence in patients with colon and rectal cancers.

MATERIALS AND METHODS

A retrospective review of 1,838 patients who underwent curative resection of non-metastatic colorectal cancer was conducted. The patients were treated between 1994 and 2004, and had a minimum follow-up of 3 years.

RESULTS

There were 994 patients with colon cancer and 844 patients with rectal cancer. The median duration of follow-up was 60.9 +/- 24.5 months. With respect to colon cancer, the local recurrence rate was 6.1% (61 patients). With respect to rectal cancer, 95 patients had a local recurrence (11.3%), the rate of which was statistically greater than the local recurrence rate for colon cancer (p < 0.001). The overall recurrence rate was 16.4% (301 patients), and the local recurrence rate, with or without systemic metastases, was 8.5% (156 patients). Local recurrences occurred within 2 and 3 years in 59.9% and 82.4% of the patients, respectively. In patients with colon and rectal cancer, the pathologic T stage (p = 0.044 and p = 0.034, respectively), pathologic N stage (p = 0.001 and p < 0.001, respectively), and lymphovascular invasion (p = 0.013 and p = 0.004, respectively) were adverse risk factors for local recurrence. The level of the anastomosis from the anal verge was an additional prognostic factor (p = 0.007) in patients with rectal cancer.

CONCLUSION

Compulsive follow-up care of patients with colon and rectal cancers is needed for 3 years after curative resection, especially in patients who have adverse risk factors for local recurrence.

Single-detector polarization-sensitive optical frequency domain imaging using high-speed intra A-line polarization modulation

We demonstrate a novel high-speed polarization-sensitive optical frequency domain imaging system employing high-speed polarization modulation. Rapid and continuous polarization modulation of light prior to illumination of the sample is accomplished by shifting the frequency of one polarization eigenstate by an amount equal to one quarter of the digitization sampling frequency. This approach enables polarization-sensitive imaging with a single detection channel and overcomes artifacts that may arise from temporal variations of the birefringence in fiber-optic imaging probes and spatial variation of birefringence in the sample.

Functional analyses of heterotrimeric G protein G alpha and G beta subunits in Gibberella zeae

The homothallic ascomycete fungus Gibberella zeae (anamorph: Fusarium graminearum) is a major toxigenic plant pathogen that causes head blight disease on small-grain cereals. The fungus produces the mycotoxins deoxynivalenol (DON) and zearalenone (ZEA) in infected hosts, posing a threat to human and animal health. Despite its agricultural and toxicological importance, the molecular mechanisms underlying its growth, development and virulence remain largely unknown. To better understand such mechanisms, we studied the heterotrimeric G proteins of G. zeae, which are known to control crucial signalling pathways that regulate various cellular and developmental responses in fungi. Three putative Gα subunits, GzGPA1, GzGPA2 and GzGPA3, and one Gβ subunit, GzGPB1, were identified in the F. graminearum genome. Deletion of GzGPA1, a homologue of the Aspergillus nidulans Gα gene fadA, resulted in female sterility and enhanced DON and ZEA production, suggesting that GzGPA1 is required for normal sexual reproduction and repression of toxin biosynthesis. The production of DON and ZEA was also enhanced in the GzGPB1 mutant, suggesting that both GαGzGPA1 and GβGzGPB1 negatively control mycotoxin production. Deletion of GzGPA2, which encodes a Gα protein similar to A. nidulans GanB, caused reduced pathogenicity and increased chitin accumulation in the cell wall, implying that GzGPA2 has multiple functions. Our study shows that G. zeae heterotrimeric G protein subunits can regulate vegetative growth, sexual development, toxin production and pathogenicity.

Identification of differentially expressed proteins in a mat1-2-deleted strain of Gibberella zeae, using a comparative proteomics analysis

Gibberella zeae is a self-fertile ascomycetous fungus that causes important diseases of cereal crops. A comprehensive understanding of sexual reproduction in G. zeae is needed for disease control. To identify fungal proteins involved in this process, we compared the protein profiles of a wild-type strain and its self-sterile strain deleted for MAT1-2, a master regulator of sexual reproduction in G. zeae. Using 2-DE and either MALDI-TOF or ESI-Q-TOF MS, we identified 13 protein spots that showed statistically significant differences in expression levels between the two strains; 11 were reduced and two were increased in abundance in the DeltaMAT1-2 strain. Six of the 13 proteins were similar to those related to cell wall structure and the others were orthologs of proteins involved in metabolism or environmental stress responses. We confirmed that all the genes of the proteins examined were down-regulated during the sexual development stage in the DeltaMAT1-2, DeltaMAT1-1, and other strains deleted for a MAP kinase or a G-protein gene. These data suggest that differences in the protein expression levels are mostly affected by down-regulation of the corresponding genes in the DeltaMAT1-2 strain. To date, this is the first proteomics approach successfully identifying proteins differentially regulated by MAT1-2 in G. zeae.

High-speed polarization sensitive optical frequency domain imaging with frequency multiplexing

Polarization sensitive optical coherence tomography (PS-OCT) provides a cross-sectional image of birefringence in biological samples that is complementary in many applications to the standard reflectance-based image. Recent ex vivo studies have demonstrated that birefringence mapping enables the characterization of collagen and smooth muscle concentration and distribution in vascular tissues. Instruments capable of applying these measurements percutaneously in vivo may provide new insights into coronary atherosclerosis and acute myocardial infarction. We have developed a polarization sensitive optical frequency domain imaging (PS-OFDI) system that enables high-speed intravascular birefringence imaging through a fiber-optic catheter. The novel design of this system utilizes frequency multiplexing to simultaneously measure reflectance of two incident polarization states, overcoming concerns regarding temporal variations of the catheter fiber birefringence and spatial variations in the birefringence of the sample. We demonstrate circular cross-sectional birefringence imaging of a human coronary artery ex vivo through a flexible fiber-optic catheter with an A-line rate of 62 kHz and a ranging depth of 6.2 mm.

A novel F-box protein involved in sexual development and pathogenesis in Gibberella zeae

Gibberella zeae is an ascomyceteous fungus that causes serious diseases in cereal crops. Severe epidemics require strains that are virulent and that can reproduce sexually. We characterized an insertional mutant (designated ZH436) with a pleiotropic defect in both traits, and identified a novel F-box protein gene encoding FBP1 (F-box protein 1) that is similar to fungal F-box proteins including Saccharomyces cerevisiae Grr1, a well-characterized component of the Skp1-Cullin-F-box protein (SCF(Grr1)) E3 ligase complex required for protein degradation. FBP1 also can bind both S. cerevisiae Skp1 protein, the other component of the SCF(Grr1) complex, and its G. zeae sequence homologue SKP1. Two putative protein interacting domains in FBP1 are essential for in vivo function. FBP1 and ScGRR1 are not so interchangeable between S. cerevisiae and G. zeae, but FBP1 can partially complement several defects of a yeast grr1 deletion mutant. Functional analyses confirmed that FBP1 is required for several phenotypes including both sexual development and virulence in G. zeae; the phenotype of DeltaFBP1 strains is different from those of null mutants for F-box proteins in other filamentous fungi as well as from S. cerevisiae grr1Delta strains. Thus, FBP1 is a versatile F-box protein that presumably participates in the formation of the SCF(FBP1) complex that probably controls the ubiquitin-mediated degradation of proteins involved in sexual reproduction and virulence important for disease development by G. zeae.

Decision for salvage treatment after transanal endoscopic microsurgery

BACKGROUND

Transanal endoscopic microsurgery (TEM) has emerged as an alternative to classic radical operation for early rectal cancer. Early rectal cancer can be treated by adequate local excision such as TEM. If there are adverse risk factors, especially poor cellular differentiation, close resection margin, or positive lymphovascular invasion or incomplete excision, a radical resection is indicated. This study aimed to clarify the factors related to recurrence for patients required to undergo a salvage operation after TEM.

METHODS

This retrospective study analyzed 167 patients who underwent TEM for rectal cancer between 1994 and 2004. Of these patients, 36 with poor differentiation, mucinous carcinoma, proper muscle invasion, lymphovascular invasion, and positive resection margin were included in the analysis.

RESULTS

Of the 36 patients, 12 underwent a salvage operation, and the remaining 24 did not because of poor physical condition or refusal of radical surgery. There were a total of 6 (16.7%) recurrences. One (8.3%) of the 12 patients who underwent salvage surgery had systemic recurrence. Five (20.8%) of the 24 patients who did not receive surgery had recurrence (3 local recurrences, 2 distant recurrences). Analysis of the subgroups showed that 2 (28.6%) of 7 patients with lymphovascular invasion had recurrence, and that 1 patient (100%) had a T3 lesion. Three (17.6%) of 17 patients had T2 lesions.

CONCLUSIONS

For high-risk patients, TEM followed by radical surgery is the most beneficial in preventing local recurrence. Radical salvage surgery is strongly recommended if pathologic results after TEM show T3 lesion or lymphovascular invasion.

Functional characterization of acetylglutamate synthase and phosphoribosylamine-glycine ligase genes in Gibberella zeae

Gibberella zeae (anamorph, Fusarium graminearum) is an important pathogen of cereal crops found in many regions of the world. In this study, we have characterized two auxotrophic strains, designated S4B1279 and S4B3008, which were discovered from a collection of insertional mutants of G. zeae generated by restriction enzyme-mediated integration (REMI). Both mutant strains exhibited pleiotropic phenotypic changes that include reduction of mycelial growth and virulence and abolished sexual reproduction. Molecular analysis of the REMI mutants has shown that the auxotrophy of S4B1279 is due to a mutation of the ARG2 gene encoding an acetylglutamate synthase, and the auxotrophy of S4B3008 is due to a mutation of the ADE5 gene encoding a phosphoribosylamine-glycine ligase. Subsequent gene disruption and complementation studies have confirmed the functions for ARG2 and ADE5, respectively, in G. zeae. Our study has demonstrated the feasibility of using the REMI technique in studying G. zeae virulence mechanisms, in addition to providing two new selectable markers allowing genetic transformation of the fungus.

Prognostic Significance of β-catenin in Colorectal Cancer with Liver Metastasis

AIMS

A decreased expression of beta-catenin has been known to be associated with tumour metastasis. The prognostic value of beta-catenin expression in colorectal cancer (CRC) patients with liver metastasis was evaluated.

MATERIALS AND METHODS

Seventy patients who underwent curative resection for CRC with liver metastasis were included. Tissue samples from normal colon mucosa, primary CRC and metastatic liver lesions were prepared in tissue microarrays, and were stained by immunohistochemistry with beta-catenin antibody. The beta-catenin expression of primary CRC tissues and metastatic liver tissues was analysed.

RESULTS

A high expression of beta-catenin (score > 6) was observed in 42.0% and 21.9% of primary colorectal tissues and metastatic liver tissues, respectively. The beta-catenin expression in metastatic liver tissues was significantly lower than in primary CRC tissues (P = 0.022). The patients were classified into two groups according to the difference in the beta-catenin expression score between the primary CRC and the liver metastasis. Group A was defined as patients showing a remarkably decreased expression of beta-catenin in their metastatic liver tissue and group B was defined as patients showing a maintained or increased beta-catenin expression in their metastatic liver tissue in comparison with their primary CRC. The overall survival and disease-free survival rates were better in group B than in group A, and this was statistically significant (P = 0.02, P = 0.002).

CONCLUSION

The decreased expression of beta-catenin in a metastatic liver lesion may be a poor prognostic marker in CRC with liver metastasis and further investigation is necessary.

Optical frequency domain imaging with a rapidly swept laser in the 815-870 nm range

Optical frequency domain imaging (OFDI) in the 800-nm biological imaging window is demonstrated by using a novel wavelength-swept laser source. The laser output is tuned continuously from 815 to 870 nm at a 43.2-kHz repetition rate with 7-mW average power. Axial resolution of 10-mum in biological tissue and peak sensitivity of 96 dB are achieved. In vivo imaging of Xenopus laevis is demonstrated with an acquisition speed of 84 frames per second (512 axial lines per frame). This new imaging technique may prove useful in comprehensive retinal screening for medical diagnosis and contrast-agent-based imaging for biological investigations.

Two different polyketide synthase genes are required for synthesis of zearalenone in Gibberella zeae

Zearalenone (ZEA) is a polyketide mycotoxin produced by some species of Gibberella/Fusarium and causes hyperestrogenic syndrome in animals. ZEA occurs naturally in cereals infected by Gibberella zeae in temperate regions and threatens animal health. In this study, we report on a set of genes that participate in the biosynthesis of ZEA in G. zeae. Focusing on the non-reducing polyketide synthase (PKS) genes of the G. zeae genome, we demonstrated that PKS13 is required for ZEA production. Subsequent analyses revealed that a continuous, 50 kb segment of DNA carrying PKS13 consisted of three additional open reading frames that were coexpressed as a cluster during the condition for ZEA biosynthesis. These genes, in addition to PKS13, were essential for the ZEA biosynthesis. They include another PKS gene (PKS4) encoding a fungal reducing PKS; zearalenone biosynthesis gene 1 (ZEB1), which shows a high similarity to putative isoamyl alcohol oxidase genes; and ZEB2 whose deduced product carries a conserved, basic-region leucine zipper domain. ZEB1 is responsible for the chemical conversion of beta-zearalenonol (beta-ZOL) to ZEA in the biosynthetic pathway, and ZEB2 controls transcription of the cluster members. Transcription of these genes was strongly influenced by different culture conditions such as nutrient starvations and ambient pH. Furthermore, the same set of genes regulated by ZEB2 was dramatically repressed in the transgenic G. zeae strain with the deletion of PKS13 or PKS4 but not in the ZEB1 deletion strain, suggesting that ZEA or beta-ZOL may be involved in transcriptional activation of the gene cluster required for ZEA biosynthesis in G. zeae. This is the first published report on the molecular characterization of genes required for ZEA biosynthesis.

Functional identification of high-affinity iron permeases from Fusarium graminearum

The ScFTR1 gene encodes an iron permease in Saccharomyces cerevisiae. Its homologues, FgFtr1 and FgFtr2, were identified from filamentous pathogenic plant fungus, Fusarium graminearum. Homologies between the deduced amino acid sequences of ScFtr1p and FgFtr1 and FgFtr2 were 56 and 54%, respectively, and both had REXXE sequences, which form the conserved amino acid sequence of ScFtr1p. FgFtr1 expression increased under iron depletion, and although FgFtr2 mRNA was not detected in the wild-type strain, it was detected in the deltafgftr1 strain in the iron-depleted condition. When the FgFtr1 and FgFtr2 were deleted, the amount of growth was found not to be different from the wild-type in iron-depleted media. However, the mRNA of FgSid, a homologue of the SIDA of Aspergillus fumigatus, was dramatically increased in the deltafgftr1/deltafgftr2 strain and in an iron-depleted condition. FgFtr1 and FgFtr2 genes act as functional complements when they are introduced into the S. cerevisiae deltaScftr1 strain. The deltaScftr1 strain, which contains either the FgFtr1 or FgFtr2, grew well in iron-depleted media. Moreover, specific alteration of the REXXE consensus sequence of FgFtr1 and FgFtr2 did not allow for sustained growth of the deltaScftr1 strain on iron-depleted medium. The iron uptake activity was recovered when FgFtr1 and FgFtr2 genes were introduced into the deltaScftr1 strain. Though the Fet3p in S. cerevisiae was found on the intracellular vesicle in the deltaScftr1 strain, Fet3p was found on the plasma membrane when FgFtr1 or FgFtr2 was introduced into the deltaftr1 strain. An infection test was carried out with deletion strains; however, no change in the ability of these strains to cause disease was observed. These results suggest that FgFtr1 and FgFtr2 may function as iron permeases in the reductive iron uptake pathway and that they do not play major roles in the pathogenicity of F. graminearum.

Numerical study of wavelength-swept semiconductor ring lasers: the role of refractive-index nonlinearities in semiconductor optical amplifiers and implications for biomedical imaging applications

Recent results have demonstrated unprecedented wavelength-tuning speed and repetition rate performance of semiconductor ring lasers incorporating scanning filters. However, several unique operational characteristics of these lasers have not been adequately explained, and the lack of an accurate model has hindered optimization. We numerically investigated the characteristics of these sources, using a semiconductor optical amplifier (SOA) traveling-wave Langevin model, and found good agreement with experimental measurements. In particular, we explored the role of the SOA refractive-index nonlinearities in determining the intracavity frequency-shift-broadening and the emitted power dependence on scan speed and direction. Our model predicts both continuous-wave and pulse operation and shows a universal relationship between the output power of lasers that have different cavity lengths and the filter peak frequency shift per round trip, therefore revealing the advantage of short cavities for high-speed biomedical imaging.

Evaluation of a modified antimycobacterial susceptibility test using Middlebrook 7H10 agar containing 2,3-diphenyl-5-thienyl-(2)-tetrazolium chloride

A rapid and accurate antimycobacterial susceptibility test is essential for effective treatment of tuberculosis. The aim of this study was to evaluate a modified method applying 2,3-diphenyl-5-thienyl-(2)-tetrazolium chloride (STC) to the Clinical and Laboratory Standards Institute (CLSI) guideline for susceptibility testing of Mycobacterium tuberculosis. A total of 132 clinical isolates of M. tuberculosis, forty-eight isolates showing resistance to one or more of the first-line antituberculosis drugs, and eighty-four fully susceptible isolates were collected from hospitals of a nationwide distribution from June to September 2004. The modified procedure was conducted basically according to the agar-proportion method described in the CLSI Guideline both with STC 50 mug/mL. The amount of growth in each well was recorded and graded at 2nd and 3rd weeks after inoculation. After 3 weeks of incubation, the diagnostic sensitivity and specificity for the detection of drug-resistant strains of STC-containing agar proportion methods were 100%, except ethambutol-low level resistance, of which the diagnostic sensitivity was 93.4%. After two weeks of incubation in STC-containing agar proportion methods, one hundred of the 107 strain-drug combinations have shown drug resistance, indicating the sensitivity of 93.5%. Especially, all 41 isoniazid-resistant strains and 19 of 21 rifampin-resistant strains (90.5%) could be detected after two weeks of incubation. A modification of the agar proportion method using STC resulted in a reliable and more easily interpretable data, and detected most of resistant strains a week earlier than conventional method.