NbSOBIR1 Partitions Into Plasma Membrane Microdomains and Binds ER-Localized NbRLP1

The receptor-like kinase Suppressor of BIR1 (SOBIR1) binds various receptor-like proteins (RLPs) that perceive microbe-associated molecular patterns (MAMPs) at the plasma membrane, which is thought to activate plant pattern-triggered immunity (PTI) against pathogen invasion. Despite its potentially crucial role, how SOBIR1 transmits immune signaling to ultimately elicit PTI remains largely unresolved. Herein, we report that a Nicotiana benthamiana gene NbRLP1, like NbSOBIR1, was highly induced upon Phytophthora parasitica infection. Intriguingly, NbRLP1 is characterized as a receptor-like protein localizing to the endoplasmic reticulum (ER) membrane rather than the plasma membrane. Using bimolecular fluorescence complementation and affinity purification assays, we established that NbRLP1 is likely to associate with NbSOBIR1 through the contact between the ER and plasma membrane. We further found that NbSOBIR1 at the plasma membrane partitions into mobile microdomains that undergo frequent lateral movement and internalization. Remarkably, the dynamics of NbSOBIR1 microdomain is coupled to the remodeling of the cortical ER network. When NbSOBIR1 microdomains were induced by the P. parasitica MAMP ParA1, tobacco cells overexpressing NbRLP1 accelerated NbSOBIR1 internalization. Overexpressing NbRLP1 in tobacco further exaggerated the ParA1-induced necrosis. Together, these findings have prompted us to propose that ER and the ER-localized NbRLP1 may play a role in transmitting plant immune signals by regulating NbSOBIR1 internalization.

Soil Is Not a Reservoir for Phellinus noxius

Phellinus noxius causes brown root rot (BRR) of diverse trees. Basidiospores and diseased host tissues have been recognized as important sources of P. noxius inoculum. This study aimed to understand whether P. noxius could occur or survive in soil without host tissues in the natural environment. Soil was sampled before and after the removal of diseased trees at eight BRR infection sites (total of 44 samples). No P. noxius colonies were recovered in soil plating assays, suggesting that no or little viable P. noxius resided in the soil. To know whether P. noxius could disseminate from decayed roots to the surrounding soil, rhizosphere and non-rhizosphere soils were sampled from another two infection sites. Although P. noxius DNA was detectable with specific primers, no P. noxius could be isolated, even from the rhizosphere soils around decayed roots covered with P. noxius mycelial mats. The association between viable P. noxius and the presence of its DNA was also investigated using field soil mixed with P. noxius arthrospores. After P. noxius was exterminated by flooding or fumigation treatment, its DNA remained detectable for a few weeks. The potential of onsite soil as an inoculum was tested using the highly susceptible loquat (Eriobotrya japonica). Loquats replanted in an infection site that had been cleaned up by simply removing the diseased stump and visible residual roots remained healthy for a year. Taken together, P. noxius is not a soilborne pathogen, and diseased host tissues should be the focus of field sanitation and detection for BRR.

Two genes encoding GH10 xylanases are essential for the virulence of the oomycete plant pathogen Phytophthora parasitica

Plant cell walls are pivotal battlegrounds between microbial pathogens and their hosts. To penetrate the cell wall and thereby to facilitate infection, microbial pathogens are equipped with a wide array of cell wall-degrading enzymes to depolymerize the polysaccharides in the cell wall. However, many of these enzymes and their role in the pathogenesis of microbial pathogens are not characterized, especially those from Oomycetes. In this study, we analyzed the function of four putative endo-beta-1,4-xylanase-encoding genes (ppxyn1-ppxyn4) from Phytophthora parasitica, an oomycete plant pathogen known to cause severe disease in a wide variety of plant species. All four genes belong to the glycoside hydrolase family 10 (GH10). Recombinant proteins of ppxyn1, ppxyn2, and ppxyn4 obtained from the yeast Pichia pastoris showed degrading activities toward birch wood xylan, but they behaved differently in terms of the conditions for optimal activity, thermostability, and durability. Quantitative RT-PCR revealed upregulated expression of all four genes, especially ppxyn1 and ppxyn2, during plant infection. In contrast, ppxyn3 was highly expressed in cysts and its close homolog, ppxyn4, in germinating cysts. To uncover the role of ppxyn1 and ppxyn2 in the pathogenesis of P. parasitica, we generated silencing transformants for these two genes by double-stranded RNA-mediated gene silencing. Silencing ppxyn1 and ppxyn2 reduced the virulence of P. parasitica toward tobacco (Nicotiana benthamiana) and tomato plants. These results demonstrate the crucial role of xylanase-encoding ppxyn1 and ppxyn2 in the infection process of P. parasitica.

Phellinus noxius: molecular diversity among isolates from Taiwan and its phylogenetic relationship with other species of Phellinus based on sequences of the ITS region

BACKGROUND

Analysis of phylogenetic relationship of 91 isolates of Phellinus noxius obtained from 46 plant species in Taiwan did not show distinct grouping based on ITS sequences.

RESULTS

However, the ITS nucleotides showed 20 different kinds of variations including single nucleotide polymorphisms, deletion and insertion in ITS1 and ITS2, but none in 5.8 S. The Taiwanese isolates of P. noxius were dividable into long (type L), median (type M) and short (type S) groups based on ITS sequence length. Two isolates with identical ITS sequence belonged to types L. Type M with 72 isolates was further divided into 33 subtypes, while types S with 17 isolates was further divided into two subtypes.

CONCLUSION

Phylogenetic analysis of ITS sequences among Phellinus species showed that isolates of P. noxius were in the same clade distinctly separated from other Phellinus species.

PpMID1 Plays a Role in the Asexual Development and Virulence of Phytophthora parasitica

Phytophthora parasitica is a notorious oomycete pathogen that causes severe disease in a wide variety of crop species. Infection of plants involves mainly its asexual life stage, including papillate sporangia and biflagellated zoospores, which are the primary dispersal and infection agents of this pathogen. Calcium signaling has been thought as the key regulator for sporangium formation and zoospore differentiation. However, not much is known about the molecular players involved in these processes. In Saccharomyces cerevisiae, mating pheromone-induced death 1 (MID1) encodes a component of a putative calcium channel. Here, we identified and characterized the function of PpMID1, an MID1 homolog from P. parasitica. The expression of PpMID1 was high in sporangia. Gene silencing of PpMID1 resulted in the formation of sporangia that lacked papilla and showed a tendency for direct germination. Notably, in response to cold shock to induce zoospore formation, these sporangia showed no sign of cytoplasmic cleavage and thereby failed to form zoospores. Nonetheless, the addition of CaCl₂ or MgCl₂ partially recovered the silenced sporangia phenotype, with the formation of papillate sporangia similar to those of the wild type and the release of zoospores upon cold shock. As well, virulence toward Nicotiana benthamiana was reduced in the PpMID1-silenced transformants. These results indicate a role of PpMID1 in the asexual development and virulence of P. parasitica.

pks63787, a Polyketide Synthase Gene Responsible for the Biosynthesis of Benzenoids in the Medicinal Mushroom Antrodia cinnamomea

Antrodia cinnamomea, a unique resupinate basidiomycete endemic to Taiwan, has potent medicinal activities. The reddish basidiocarps and mycelia generally exhibit abundant metabolites and higher biological activity. To investigate the pigments of A. cinnamomea, polyketide synthase (PKS) genes were characterized based on its partially deciphered genome and the construction of a fosmid library. Furthermore, a gene disruption platform was established via protoplast transformation and homologous recombination. Of four putative polyketide synthase genes, pks63787 was selected and disrupted in the monokaryotic wild-type (wt) strain f101. Transformant Δpks63787 was deficient in the synthesis of several aromatic metabolites, including five benzenoids and two benzoquinone derivatives. Based on these results, a biosynthetic pathway for benzenoid derivatives was proposed. The pks63787 deletion mutant not only displayed a reduced red phenotype compared to the wt strain but also displayed less 1,1-biphenyl-2-picrylhydrazyl free radical scavenging activity. This finding suggests that PKS63787 is responsible for the biosynthesis of pigments and metabolites related to the antioxidant activity of A. cinnamomea. The present study focuses on the functional characterization of the PKS gene, the fluctuations of its profile of secondary metabolites, and interpretation of the biosynthesis of benzenoids.

Development of oligonucleotide microarrays for simultaneous multi-species identification of Phellinus tree-pathogenic fungi

Polyporoid Phellinus fungi are ubiquitously present in the environment and play an important role in shaping forest ecology. Several species of Phellinus are notorious pathogens that can affect a broad variety of tree species in forest, plantation, orchard and urban habitats; however, current detection methods are overly complex and lack the sensitivity required to identify these pathogens at the species level in a timely fashion for effective infestation control. Here, we describe eight oligonucleotide microarray platforms for the simultaneous and specific detection of 17 important Phellinus species, using probes generated from the internal transcribed spacer regions unique to each species. The sensitivity, robustness and efficiency of this Phellinus microarray system was subsequently confirmed against template DNA from two key Phellinus species, as well as field samples collected from tree roots, trunks and surrounding soil. This system can provide early, specific and convenient detection of Phellinus species for forestry, arboriculture and quarantine inspection, and could potentially help to mitigate the environmental and economic impact of Phellinus-related diseases.

The Genetic Structure of Phellinus noxius and Dissemination Pattern of Brown Root Rot Disease in Taiwan

Since the 1990s, brown root rot caused by Phellinus noxius (Corner) Cunningham has become a major tree disease in Taiwan. This fungal pathogen can infect more than 200 hardwood and softwood tree species, causing gradual to fast decline of the trees. For effective control, we must determine how the pathogen is disseminated and how the new infection center of brown root rot is established. We performed Illumina sequencing and de novo assembly of a single basidiospore isolate Daxi42 and obtained a draft genome of ~40 Mb. By comparing the 12,217 simple sequence repeat (SSR) regions in Daxi42 with the low-coverage Illumina sequencing data for four additional P. noxius isolates, we identified 154 SSR regions with potential polymorphisms. A set of 13 polymorphic SSR markers were then developed and used to analyze 329 P. noxius isolates collected from 73 tree species from urban/agricultural areas in 14 cities/counties all around Taiwan from 1989 to 2012. The results revealed a high proportion (~98%) of distinct multilocus genotypes (MLGs) and that none of the 329 isolates were genome-wide homozygous, which supports a possible predominant outcrossing reproductive mode in P. noxius. The diverse MLGs exist as discrete patches, so brown root rot was most likely caused by multiple clones rather than a single predominant strain. The isolates collected from diseased trees near each other tend to have similar genotype(s), which indicates that P. noxius may spread to adjacent trees via root-to-root contact. Analyses based on Bayesian clustering, FST statistics, analysis of molecular variance, and isolation by distance all suggest a low degree of population differentiation and little to no barrier to gene flow throughout the P. noxius population in Taiwan. We discuss the involvement of basidiospore dispersal in disease dissemination.

Tomato SOBIR1/EVR Homologs Are Involved in Elicitin Perception and Plant Defense Against the Oomycete Pathogen Phytophthora parasitica

During host-pathogen interactions, pattern recognition receptors form complexes with proteins, such as receptor-like kinases, to elicit pathogen-associated molecular pattern-triggered immunity (PTI), an evolutionarily conserved plant defense program. However, little is known about the components of the receptor complex, as are the molecular events leading to PTI induced by the oomycete Phytophthora pathogen. Here, we demonstrate that tomato (Solanum lycopersicum) SlSOBIR1 and SlSOBIR1-like genes are involved in defense responses to Phytophthora parasitica. Silencing of SlSOBIR1 and SlSOBIR1-like enhanced susceptibility to P. parasitica in tomato. Callose deposition, reactive oxygen species production, and PTI marker gene expression were compromised in SlSOBIR1- and SlSOBIR1-like-silenced plants. Interestingly, P. parasitica infection and elicitin (ParA1) treatment induced the relocalization of SlSOBIR1 from the plasma membrane to endosomal compartments and silencing of NbSOBIR1 compromised ParA1-mediated cell death on Nicotiana benthamiana. Moreover, the SlSOBIR1 kinase domain is indispensable for ParA1 to trigger SlSOBIR1 internalization and plant cell death. Taken together, these results support the idea of participation of solanaceous SOBIR1/EVR homologs in the perception of elicitins and indicate their important roles in plant basal defense against oomycete pathogens.

A novel elicitor protein from Phytophthora parasitica induces plant basal immunity and systemic acquired resistance

The interaction between Phytophthora pathogens and host plants involves the exchange of complex molecular signals from both sides. Recent studies of Phytophthora have led to the identification of various apoplastic elicitors known to trigger plant immunity. Here, we provide evidence that the protein encoded by OPEL of Phytophthora parasitica is a novel elicitor. Homologues of OPEL were identified only in oomycetes, but not in fungi and other organisms. Quantitative reverse transcription-polymerase chain reaction (RT-PCR) revealed that OPEL is expressed throughout the development of P. parasitica and is especially highly induced after plant infection. Infiltration of OPEL recombinant protein from Escherichia coli into leaves of Nicotiana tabacum (cv. Samsun NN) resulted in cell death, callose deposition, the production of reactive oxygen species and induced expression of pathogen-associated molecular pattern (PAMP)-triggered immunity markers and salicylic acid-responsive defence genes. Moreover, the infiltration conferred systemic resistance against a broad spectrum of pathogens, including Tobacco mosaic virus, the bacteria wilt pathogen Ralstonia solanacearum and P. parasitica. In addition to the signal peptide, OPEL contains three conserved domains: a thaumatin-like domain, a glycine-rich protein domain and a glycosyl hydrolase (GH) domain. Intriguingly, mutation of a putative laminarinase active site motif in the predicted GH domain abolished its elicitor activity, which suggests enzymatic activity of OPEL in triggering the defence response.

Generation and analysis of the expressed sequence tags from the mycelium of Ganoderma lucidum

Ganoderma lucidum (G. lucidum) is a medicinal mushroom renowned in East Asia for its potential biological effects. To enable a systematic exploration of the genes associated with the various phenotypes of the fungus, the genome consortium of G. lucidum has carried out an expressed sequence tag (EST) sequencing project. Using a Sanger sequencing based approach, 47,285 ESTs were obtained from in vitro cultures of G. lucidum mycelium of various durations. These ESTs were further clustered and merged into 7,774 non-redundant expressed loci. The features of these expressed contigs were explored in terms of over-representation, alternative splicing, and natural antisense transcripts. Our results provide an invaluable information resource for exploring the G. lucidum transcriptome and its regulation. Many cases of the genes over-represented in fast-growing dikaryotic mycelium are closely related to growth, such as cell wall and bioactive compound synthesis. In addition, the EST-genome alignments containing putative cassette exons and retained introns were manually curated and then used to make inferences about the predominating splice-site recognition mechanism of G. lucidum. Moreover, a number of putative antisense transcripts have been pinpointed, from which we noticed that two cases are likely to reveal hitherto undiscovered biological pathways. To allow users to access the data and the initial analysis of the results of this project, a dedicated web site has been created at http://csb2.ym.edu.tw/est/.

First Report of Fruit Rot Disease of Mango Caused by Botryosphaeria dothidea and Neofusicoccum mangiferae in Taiwan

Mango (Mangifera indica L.) is an economically important fruit crop in the tropical and subtropical areas of the world. In southern Taiwan, mango is grown on 18,000 ha of hilly land mainly located in Tainan, Kaohsiung, and Pingtung. Tons (180,000) of mango with a value of NT$6.6 billion (US$206 million) are produced annually. In 2008, mango fruit rot disease was observed 1 week after harvest on 30 to 72% of stored mangoes collected from seven orchards in southern Taiwan. The initial symptom was a small, brown lesion and rot symptoms advanced progressively. Two predominant fungi were isolated from the margin of lesions on acidified potato dextrose agar (PDA with lactic acid, pH 3.8). Isolates of each fungal type were transferred to 2% water agar containing sterilized pine needles and exposed to near UV light to induce sporulation. For the first fungus, conidia obtained from pycnidia were ovate, one-celled, and hyaline, with an average length and width of 12.93 ± 0.93 × 6.98 ± 0.40 μm and an average length/width ratio of 1.85. To confirm the identity of the fungus, PCR amplification by universal primers, ITS1/ITS4, and DNA sequencing of the internal transcribed spacer (ITS1-5.8S-ITS2 rRNA gene cluster) were conducted. The internal transcribed spacer (ITS) sequence of ribosomal DNA of this fungus was analyzed and submitted to GenBank (Accession No. GQ421486). It showed a sequence identity of 100% with Neofusicoccum mangiferae (Syd. & P. Syd.) Crous, Slippers & A. J. L. Phillips) (GenBank Accession No. AY615185). For the second fungus, conidia obtained from pycnidia were fusiform, one-celled, and hyaline, with an average length and width of 22.87 ± 1.32 × 6.42 ± 0.46 μm and a length/width ratio of 3.53. The ITS sequence of ribosomal DNA of this fungus was analyzed and submitted to GenBank (Accession No. GQ421485). It showed a sequence identity of 100% with Botryosphaeria dothidea (Moug.: Fr.) Ces & De Not.) (GenBank Accession No. AY 786321). To test pathogenicity, four mango fruits were wounded with a sterile needle, inoculated with mycelium agar plugs (0.5 mm in diameter) excised from separate monoconidial cultures, and incubated in a plastic box with a 100% relative humidity for 2 days at room temperature. Brown lesions appeared on all wounded sites of each fungus 2 days postinoculation. In control experiments, sterile agar plugs were placed on the wounded mango fruits. These fruits remained completely free from symptoms throughout the experiment. The pathogen was reisolated from the lesions of inoculated fruits and identified as N. mangiferae and B. dothidea, thus fulfilling Koch's postulates. N. mangiferae and B. dothidea have been reported on mango trees in Australia and South Africa (1). To our knowledge, this is the first report of these fungi causing fruit rot of mango in Taiwan. References: (1) B. Slippers et al. Mycologia 97:99, 2005.

First Report of a Fruit Rot Disease of Avocado Caused by Neofusicoccum mangiferae

Production of avocado (Persea americana) has increased significantly during the last 10 years in Taiwan and the area of cultivation is approximately 500 ha. The most important postharvest disease of avocado is anthracnose caused by Colletotrichum gloeosporioides (Penz.) in Taiwan (1). In 2008, a new disease was found to be infecting avocado fruit at some orchards in Tainan County of southern Taiwan. Infected avocados developed smooth, brown, circular spots first on the surface of harvested fruits. A fungus was always isolated from the margin of lesions and could also be found from symptomless fruit pedicles and stems. Fungal colonies cultured on acidified potato dextrose agar (PDA with lactic acid; pH 3.8) were initially colorless, turned dark gradually, and ultimately became gray to dark gray. After 4 days under fluorescent light at 25°C, pycnidia formed on PDA. Conidia obtained from fruiting bodies were ovate, one celled, and hyaline, with an average length and width of 12.9 (9.9 to 15.6) × 6.4 (5.2 to 7.2) μm. The internal transcribed spacer (ITS) sequence of ribosomal DNA of this fungus was analyzed and submitted to GenBank (No. EU847427). It showed a sequence identity of 99% with Neofusicoccum mangiferae ((Syd. & P. Syd.) Crous, Slippers & A.J.L. Phillips) (GenBank No. AY615185). Thus, both morphological and molecular results confirmed the isolated fungus as N. mangiferae. Five avocado fruits were used to test the pathogenicity with three different treatment inoculation sites on each fruit. Wounded and unwounded sites on fruit were inoculated with mycelia agar plugs (0.5 mm in diameter) excised from a monoconidial culture and the fruit was kept in a plastic box with high humidity for 2 days at room temperature. Brown lesions appeared on all wounded sites 2 days postinoculation (dpi) and on unwounded sites at 4 dpi. The pathogen was reisolated from the lesions of inoculated fruits and found to be N. mangiferae, thus fulfilling Koch's postulates. In control experiments, sterile agar plugs were placed on the wounded avocado fruits. These fruits remained completely free from symptoms throughout the experiment. Several species of Botryosphaeria have been reported on avocado, including N. parvum (anamorph of B. parva), Fusicoccum aesculi (anamorph of B. dothidea), and Dothiorella aromatica (= F. luteum). To our knowledge, this is the first report of N. mangiferae causing fruit rot of avocado in Taiwan. Previously, N. mangiferae has been reported on mango trees worldwide, especially in Australia and Thailand (2). The presence of N. mangiferae in the subtropical area presents a serious disease problem not only to avocado but also to mango. References: (1) Y. P. Tsai, ed. List of Plant Diseases in Taiwan. 4th ed. Taiwan Phytopathological Society, 2002. (2) B. Slippers et al. Mycologia 97:99, 2005.

Functional characterization of a gene family encoding Polygalacturonases in Phytophthora parasitica

Phytophthora parasitica is an oomycete plant pathogen that causes severe disease in a wide variety of plant species. In our previous study, we discovered a multigene family encoding endopolygalacturonases (endoPG) in Phytophthora parasitica. Here, we screened the genomic library of Phytophthora parasitica for the genes encoding endoPG named pppg2 through pppg10, and analyzed their functions. Results obtained by real-time quantitative reverse transcriptase-polymerase chain reaction demonstrated that some of these genes are highly induced during plant infection, which suggests their important roles in the pathogenesis of Phytophthora parasitica. Analysis by in-gel activity assay of recombinant proteins obtained from Pichia pastoris indicated that each of these genes encodes a functional endoPG. Investigation of the function of pppg genes in planta by a Potato virus X agroinfection system in tobacco revealed that each pppg caused specific effects, varying from no symptoms to dwarfism, necrosis, leaf curl, silvery leaf, and cracks in leaf stalks. Appearance of these effects depends on the expression of a pppg protein with a normal active site in the apoplast. These results indicated that each pppg plays a distinct role in the decomposition of plant cell wall.

Selection of internal control genes for real-time quantitative RT-PCR assays in the oomycete plant pathogen Phytophthora parasitica

Real-time quantitative reverse transcription-PCR (qRT-PCR) has become one of the most commonly used methods for RNA quantification in recent years. To obtain reliable results with biological significance, it is important that qRT-PCR data are normalized with a proper internal control. In this study, 18 housekeeping genes were selected and evaluated for their potential as a suitable internal control for study of gene expression in the oomycete plant pathogen Phytophthora parasitica. Analysis of qRT-PCR data using the geNorm software indicated that, although commonly used as internal controls, beta-actin (ACT) and translation elongation factor 1alpha (eEF1A) might not be the best choice due to variable expression across different life stages of P. parasitica. Instead, other genes would serve as better controls, including ubiquitin-conjugating enzyme (Ubc), WS21, and beta-tubulin (Tub-b) for 'asexual stage,' Ubc and Tub-b for 'sexual reproduction,' while Ubc and WS21 for the stage of pathogenesis, because of their constant expression levels in each given subset of RNA samples. Although normalization with more than one gene would generate more reliable results, use of a single stably expressed gene as an internal control would suffice for accurate data normalization in some experiments.

Cloning and analysis of pppg1, an inducible endopolygalacturonase gene from the oomycete plant pathogen Phytophthora parasitica

Phytophthora parasitica is an oomycete plant pathogen that causes severe disease in a wide variety of crops. Here, we report the isolation of a gene, named pppg1, which encodes an extracellular endopolygalacturonase in P. parasitica. Both cDNA and a genomic clone were isolated and sequenced. The pppg1 gene showed standard characteristics with respect to core promoter and intron sequences of Phytophthora. The predicted protein of pppg1 has a calculated molecular mass of 39.7 kDa and a pI value of 5.2, and contains a putative signal peptide of 20 amino acid residues on the N-terminus. The deduced amino acid sequence is highly conserved with those of other Phytophthora and fungal endopolygalacturonases. Analysis by reverse transcription followed by real-time quantitative polymerase chain reaction showed that transcription of pppg1 was repressed by glucose, but induced by pectin in the culture. Moreover, pppg1 is highly expressed during interaction of P. parasitica with the host plant, suggesting its involvement in the process of host infection. Heterologous expression of pppg1 in Pichia pastoris produced proteins with molecular mass ranging from 75 to 200 kDa, very likely due to differential glycosylation by the yeast. Deglycosylation of the recombinant protein resulted in a complete loss of the endopolygalacturonase activity.

Complete nucleotide sequence and genome organization of a Cactus virus X strain from Hylocereus undatus (Cactaceae)

The complete nucleotide sequence of a strain of Cactus virus X (CVX-Hu) isolated from Hylocereus undatus (Cactaceae) has been determined. Excluding the poly(A) tail, the sequence is 6614 nucleotides in length and contains seven open reading frames (ORFs). The genome organization of CVX is similar to that of other potexviruses. ORF1 encodes the putative viral replicase with conserved methyltransferase, helicase, and polymerase motifs. Within ORF1, two other ORFs were located separately in the +2 reading frame, we call these ORF6 and ORF7. ORF2, 3, and 4, which form the "triple gene block" characteristic of the potexviruses, encode proteins with molecular mass of 25, 12, and 7 KDa, respectively. ORF5 encodes the coat protein with an estimated molecular mass of 24 KDa. Sequence analysis indicated that proteins encoded by ORF1-5 display certain degree of homology to the corresponding proteins of other potexviruses. Putative product of ORF6, however, shows no significant similarity to those of other potexviruses. Phylogenetic analyses based on the replicase (the methyltransferase, helicase, and polymerase domains) and coat protein demonstrated a closer relationship of CVX with Bamboo mosaic virus, Cassava common mosaic virus, Foxtail mosaic virus, Papaya mosaic virus, and Plantago asiatica mosaic virus.

Molecular evidence that aphid-transmitted Alpinia mosaic virus is a tentative member of the genus Macluravirus

Alpinia mosaic virus (AlpMV), once assigned to the genus Potyvirus, infects primarily plants of the ginger family. To seek molecular evidence for correct classification of this virus, a cDNA clone corresponding to the 3' portion of the AlpMV genome was obtained by reverse transcriptase-PCR and TA cloning. The authenticity of the cDNA clone was confirmed by expression of the coat protein (CP) in E. coli followed by immunoblot analysis. Sequence analysis indicated that, in contrast to its low identity with all the other genera of the family Potyviridae, the deduced amino acid sequence of AlpMV CP was 42.9 - 61.9% identical to members of the genus Macluravirus. Phylogenetic analysis also demonstrated that the AlpMV CP clustered with those of Cardamom mosaic virus and Chinese yam necrotic mosaic virus. These results indicate that AlpMV should be classified as a tentative species within the genus Macluravirus rather than Potyvirus as proposed previously.

The period gene of the German cockroach and its novel linking power between vertebrate and invertebrate

Circadian clock protein PERIOD (PER) is essential for the endogenous clockworks in diverse lineages within Metazoa, but the protein sequences, the clock protein interactions, and the photic responses are variant and different between vertebrate and invertebrate PER homologs. Here we identified the German cockroach PER homologs and found it could bridge the huge phylogenetic gap and make possible a more precise protein sequence comparison between vertebrate and invertebrate PER homologs. Seven blocks of conserved regions (c1-c7) interspersed within PER proteins were defined, and two new significant homologies were found in the upstream portion of c3 region and in the c7 region, respectively. In addition, we found all dipteran insects PER homologs lack the c7 region and its following amino acid residues. Our results not only reveal the homology and divergence, but also imply the constraint and plasticity of divergent PER proteins during the course of evolution. These findings lay a solid foundation for understanding the general and divergent properties of circadian clockworks in diverse lineages within Metazoa.

First Report of Cactus virus X on Hylocereus undatus (Cactaceae) in Taiwan

Hylocereus undatus Britt. & Rose (Cactaceae), commonly known as pitaya, produces edible fruits with red thorny peel and sweet white pulp containing numerous small soft seeds. In recent years, this fruit crop has become increasingly important in Taiwan. During a survey of diseases of pitaya, some plants were found with systemic mild mottling on the stems. A virus was mechanically transmitted that caused necrotic local lesions on Chenopodium amaranticolor and chlorotic lesions on C. quinoa. This virus also caused necrotic lesions with chlorotic halos on Gomphrena globosa and small chlorotic spots followed by systemic infection in Celosia argentea. Back inoculation from C. quinoa by sap transmission caused mild mottling on pitaya similar to that observed on the naturally infected plants and thus confirmed that the agent was the cause of the mottle symptom. Electron microscopic examination of negatively stained extracts from diseased plants revealed a flexuous rod-shaped virus with a length of 480 to 520 nm. Purified viral particles contained a single major protein of approximately 26 KDa as estimated by SDS polyacrylamide gel electrophoresis. In immunodiffusion tests, this virus reacted with antiserum to Cactus X virus (CVX) (ATCC #PVAS245), but did not react with antisera to Bamboo mosaic or Papaya mosaic viruses. These results establish the identity of the virus causing mottle disease on H. undatus as a strain of CVX.

Complete nucleotide sequence of Beauveria bassiana 5.8s rRNA coding gene and flanking internal transcribed spacers

The nucleotide sequence of two clones of Beauveria bassiana in 5.8s rRNA coding gene and ITS regions were completely sequenced. The overall sequence similarity of these two clones is 96%. The identities of internal transcribed spacer (ITS) regions are 91 % (ITSI) and 100% (ITSII), respectively. Both of 5.8s rRNA sequences have 98% homology.

Conversion of a trans-spliced C. elegans gene into a conventional gene by introduction of a splice donor site

In Caenorhabditis elegans, pre-mRNAs that are trans-spliced are distinguished by the presence of an 'outron', intron-like RNA at the 5' end followed by a splice acceptor. We report that trans-splicing of the rol-6 gene can be completely suppressed simply by introducing a donor site into its 173 nt outron, at a site 50 nt upstream of the trans-splice site, thereby converting rol-6 into a conventional gene with a spliced intron near its 5' end. When the consensus donor site was inserted at sites further upstream it was less effective in replacing transplicing with cis-splicing. Surprisingly, the length of the intron was not the important variable, since lengthening of the 50 nt intron to 250 nt did not restore trans-splicing. Apparently the context into which the splice site was introduced determined the efficiency of its use. These results support the conclusion that the sole signal for trans-splicing is the presence of an outron. Clearly, cis- and trans-splice acceptor sites are interchangeable, allowing the possibility of competition between the two types of splicing.

Snake venom cardiotoxin can rapidly induce actin polymerization in intact platelets

The action of Taiwan cobra (Naja naja atra) venom cardiotoxin on rabbit platelets at 37 degrees C was characterized by observing cytoskeletal alterations and cell lysis. At a concentration of 21.4 microM the toxin produced no cell lysis within 30 s, and less than 5% of the total lactate dehydrogenase activity of intact cells was detected in the suspending medium after the interaction had proceeded for 3 min. The extent of cell lysis was proportional to toxin concentration and interaction time. Before cell lysis, the toxin caused rapid incorporation of actin monomers into cross-linked actin filaments. The actin incorporation could be inhibited by either the presence of cytochalasin B or increased CaCl2 concentration in the suspending medium. However, addition of indomethacin did not influence the toxin-induced cytoskeletal change.

Functional analysis of a C. elegans trans-splice acceptor

The rol-6 gene is trans-spliced to the 22 nt leader, SL1, 173 nt downstream of the transcription start. We have analyzed splicing in transformants carrying extrachromosomal arrays of rol-6 with mutations in the trans-splice acceptor site. This site is a close match to the consensus, UUUCAG, that is highly conserved in both trans-splice and intron acceptor sites in C. elegans. When the trans-splice site was inactivated by mutating the perfectly-conserved AG, trans-splicing still occurred, but at a cryptic site 20 nt upstream. We tested the frequency with which splicing switched from the normal site to the cryptic site when the pyrimidines at this site were changed to A's. Since most C. elegans 3' splice sites lack an obvious polypyrimidine tract, we hypothesized that these four pyrimidines might play this role, and indeed mutation of these bases caused splicing to switch to the cryptic site. We also demonstrated that a major reason the downstream site is normally favored is because it occurs at a boundary between A+U rich and non-A+U rich RNA. When the RNA between the two splice sites was made less A+U rich, splicing occurred preferentially at the upstream site.

trans-spliced Caenorhabditis elegans mRNAs retain trimethylguanosine caps

The nematode Caenorhabditis elegans has an unusual small nuclear RNA, containing a 100-nucleotide RNA molecule, spliced leader RNA, which donates its 5' 22 nucleotides to a variety of recipient RNAs by a trans-splicing reaction. The spliced leader RNA has a 5' trimethylguanosine (TMG) cap, which becomes the 5' end of trans-spliced mRNAs. We found that mature trans-spliced mRNAs were immunoprecipitable with anti-TMG cap antibodies and that TMG-containing dinucleotides specifically competed with the trans-spliced mRNAs for antibody binding. We also found that these mRNAs retained their TMG caps throughout development and that the TMG-capped mRNAs were polysome associated. Since the large majority of C. elegans mRNAs are not trans-spliced, the addition of the spliced leader and its TMG cap to a limited group of recipient RNAs may create a functionally distinct subset of mRNAs.

Interaction of snake venom cardiotoxin (a membrane-disruptive polypeptide) with human erythrocytes

The action of 7.2 microM cardiotoxin on 0.25% human erythrocytes in a plasma extender solution was studied by the interaction of toxin with intact red blood cells and subsequent hemolysis of the cells. The binding of toxin to cells was completed within 10 min, whereas the membrane rigidity was weakened in a non-lytic period for about 25 min. The toxin molecules bound almost exclusively to the membrane. The bound toxin could not be liberated with either 0.5% Triton X-100 or 0.1 N NaOH. The degree of binding was slightly reduced in the presence of 10 mM mono- and divalent inorganic salts. The action of toxin might weaken the in situ association of several proteins that are linked with band 3 protein of the membrane, thus making the cells fragile and altering the shape of the cell to a smooth sphere.

Separation of isoenzymes of glucose-6-phosphate dehydrogenase from human erythrocytes by two-dimensional gel electrophoresis

Isoelectric focusing performed in 6.0% polyacrylamide gel in the presence of 1.0 M urea separates well the various molecular forms of glucose-6-phosphate dehydrogenase from human erythrocytes. At least seven sharp bands appear in the gel pattern, which vary both in isoelectric points and in the relative intensity. Their isoelectric points are at pH 6.88 for band 1, pH 6.79 for band 2, pH 6.64 for band 3, pH 6.50 for band 4, pH 6.39 for band 5, pH 6.19 for band 6, and pH 6.10 for band 7. A second-dimensional disc electrophoresis performed in a polyacrylamide gel slab resolves each band into two components, a slow and a fast component defined according to their mobilities in the disc gel. The slow component constitutes the major portion of each band. All the seven slow components appear to be dimer having a molecular weight between 98,000-94,000. They belong to "change isomers" having identical molecular size but containing different net changes. The molecular weight of the fast components is between 66,800-50,600. These fast components might be monomer or the digested products of slow components.