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Viroids are highly structured, single-stranded, non-protein-coding circular RNA pathogens that replicate, spread and elicit severe to mild disease symptoms in sensitive host species. The functions of viroids are thought to be due to a molecular element (or elements) embedded within the small RNA molecule that recruits the host factors responsible for transcription, RNA transportation and regulation of gene expression. Coleus blumei viroid 1 (CbVd-1) is distributed worldwide and is known for its characteristic property of having an extremely high frequency of seed transmission. During our analysis of CbVd-1 seed transmission, two variants, CbVd-1/25A and CbVd-1/25UU, were shown to have distinct seed-transmission frequencies: 30 and 0 %, respectively. Seven infectious dimeric forms of CbVd-1 cDNA clones were created based on the sequences of CbVd-1/25A,CbVd-1/25UU and an additional five variants with unique loop structures in other portion(s) of the molecule, and in vitro transcripts were inoculated into viroid-free coleus seedlings. All seven CbVd-1 variants showed infectivity. Nucleotide sequence analysis of the progeny revealed that four of the five additional mutants changed to either CbVd-1/25A or CbVd-1/25UU, while, CbVd-1/25A, CbVd-1/25UU and one of the five additional mutants (CbVd-1/I2) replicated stably. As expected, CbVd-1/25A and CbVd-1/I2 were transmitted through seeds, but CbVd-1/25UU was not. CbVd-1/25A and CbVd-1/I2 shared the same nucleotide at position 25 in loop five but are different from CbVd-1/25UU at that position. Therefore, nucleotide 25 in loop five was identified as a determinant for seed transmission of CbVd-1.

Apple fruit crinkle viroid (AFCVd) is a tentative member of the genus Apscaviroid, family Pospiviroidae. AFCVd has a narrow host range and is known to infect apple, hop and persimmon as natural hosts. In this study, tomato, cucumber and wild hop have been identified as new experimental herbaceous hosts. Foliar symptoms were very mild or virtually undetectable, but fruits of infected tomato were small, cracked and distorted. These symptoms resemble those observed on some AFCVd-sensitive apple cultivars. After transfer to tomato, cucumber and wild hop, sequence changes were detected in a natural AFCVd isolate from hop, and major variants in tomato, cucumber and wild hop differed in 10, 8 or 2 nucleotides, respectively, from the predominant one in the inoculum. The major variants in tomato and cucumber were almost identical, and the one in wild hop was very similar to the one in cultivated hop. Detailed analyses of the host-dependent sequence changes that appear in a naturally occurring AFCVd isolate from hop after transfer to tomato using small RNA deep sequence data and infectivity studies with dimeric RNA transcripts followed by progeny analysis indicate that the major AFCVd variant in tomato emerged by selection of a minor variant present in the inoculum (i.e. hop) followed by one to two host-dependent de novo mutations. Comparison of the secondary structures of major variants in hop, tomato and persimmon after transfer to tomato suggested that maintenance of stem-loop structures in the left-hand half of the molecule is critical for infection.

Viroids are highly structured, single-stranded, non-protein-coding circular RNA pathogens that replicate, spread and elicit severe to mild disease symptoms in sensitive host species. The functions of viroids are thought to be due to a molecular element (or elements) embedded within the small RNA molecule that recruits the host factors responsible for transcription, RNA transportation and regulation of gene expression.

The hop metabolome important for the brewing industry and for medical purposes is endangered worldwide due to multiple viroid infections affecting hop physiology. Combinatorial biolistic hop inoculation with Citrus bark cracking viroid (CBCVd), Apple fruit crinkle viroid (AFCVd), Hop latent viroid, and Hop stunt viroid (HSVd) showed a low CBCVd compatibility with HSVd, while all other viroid combinations were highly compatible. Unlike to other viroids, single CBCVd propagation showed a significant excess of (-) over (+) strands in hop, tomato, and Nicotiana benthamiana, but not in citruses. Inoculation of hop with all viroids led to multiple infections with unstable viroid levels in individual plants in the pre- and post-dormancy periods, and to high plant mortality and morphological disorders. Hop isolates of CBCVd and AFCVd were highly stable, only minor quasispecies were detected. CBCVd caused a strong suppression of some crucial mRNAs related to the hop prenylflavonoid biosynthesis pathway, while AFCVd-caused effects were moderate. According to mRNA degradome analysis, this suppression was not caused by a direct viroid-specific small RNA-mediated degradation. CBCVd infection led to a strong induction of two hop transcription factors from WRKY family and to a disbalance of WRKY/WDR1 complexes important for activation of lupulin genes.

Hop stunt viroid (HSVd) was identified as the causal agent of a hop stunt disease, which first emerged in Japan in the 1960–80s, then in the United States and China in the 2000s, and in Slovenia in 2012. HSVd has a wide natural host range. Most hosts are symptomless carriers but some sensitive hosts develop cucumber pale fruit, citrus cachexia, and plum dapple fruit diseases. HSVd consists of 294–305 nucleotides. No conclusive host-determinants were found, however, a bias for the presence of certain sequences in certain hosts reflects viroid adaptation to hosts during a long history of viroid–host interactions.

The dahlia isolate of potato spindle tuber viroid (PSTVd) accumulates slowly and induces mild disease symptoms in tomato (Solanum lycopersicum, cv. Rutgers) plants in contrast to the intermediate isolate (PSTVd-I). The dahlia isolate (PSTVd-D) differs from PSTVd-I in eight locations: 42 and 43 in the terminal left (TL); 64/65, 311, and 312/313 in the pathogenicity (P); 118 and 126 in the variable (V); and 201 in the terminal right (TR) domains. To investigate the molecular determinants in the PSTVd-D genome responsible for the attenuation of symptom severity and lower replication/accumulation in tomato plants, a series of mutants between PSTVd-D and PSTVd-I were constructed by focusing first on the mutations in the TL and P domains in the left-hand half of the molecule. Then, more detailed analysis was performed on the three mutations at positions 118, 126, and 201 in the V and TR domains. One of these mutations is located around the boundary of the right border of the RY-motif, a predicted recognition site of Virp1, a viroid-binding protein. Of 14 mutants (seven based on PSTVd-D and the other seven based on PSTVd-I) examined, 11 propagated stably and three lost infectivity. Mutations in the TL and P domains (42U, 43C, 310U/C, and U or UU insertion to 311/312 in PSTVd mild types) majorly influenced the expression of mild-like symptoms. In contrast, when each of the mutations at 118, 126, and 201 in the V and TR domains were exchanged independently, they minimally influenced systemic accumulation and symptom expression. Mutants based on PSTVd-D with PSTVd-I-type mutations at nucleotide positions 118, 126, and/or 201 showed mild symptoms similar to PSTVd-D, but their systemic accumulation was a little faster than PSTVd-D. In contrast, mutants based on PSTVd-I with PSTVd-D-type mutations at 118, 126, and/or 201 nucleotide positions showed severe symptoms similar to PSTVd-I, and the systemic accumulation was similar to or a little slower than PSTVd-I. The nucleotide at position 201 could be changed to U, G, or A, but C was not acceptable for replication. Because introduction of C at the position 201 can change the loop structure at the right boundary of the RY-motif's consensus sequence, the loop structure may influence recognition by Virp1.

A new variant of Potato spindle tuber viroid (PSTVd) was detected for the first time from dahlia grown in Japan. The dahlia isolate of PSTVd formed a quasi-species and a major sequence variant consisting of 361 nucleotides in length, including five substitutions, three insertions, and one deletion, when compared to the intermediate strain from potato. In bioassays with the new isolate, Rutgers tomato developed mild stunting and leaf curling.

A novel gamma-methylidene-spirobutanolide spirolephtoshol (1) was isolated from ascomycetous fungus Leptosphaeria doliolum as a cytotoxic compound. The relative structure was established by the NMR analysis involving the NOE experiments. Absolute structure of the bicyclic moiety was determined by chemical derivation followed by the CD analysis. The relative and absolute stereochemistry of the side chain was established by comparison of the (1)H NMR spectra and the chiral GC chromatograms of the degradation product with the synthetic samples.

The absolute stereochemistry of altersolanol A (1) was established by observing a positive exciton couplet in the circular dichroism (CD) spectrum of the C3,C4-O-bis(2-naphthoyl) derivative 10 and by chemical correlations with known compound 8. Before the discussion, the relative stereochemistry of 1 was confirmed by X-ray crystallographic analysis. The shielding effect at C7′-OMe group by C1-O-benzoylation established the relative stereochemical relationship between the C8-C8′ axial bonding and the C1-C4/C1′-C4′ polyol moieties of alterporriols E (3), an atropisomer of the C8-C8′ dimer of 1. As 3 could be obtained by dimerization of 1 in vitro, the absolute configuration of its central chirality elements (C1-C4) must be identical to those of 1. Spectral comparison between the experimental and theoretical CD spectra supported the above conclusion. Axial stereochemistry of novel C4-O-deoxy dimeric derivatives, alterporriols F (4) and G (5), were also revealed by comparison of their CD spectra to those of 2 and 3. Chirality, 2012. © 2011 Wiley Periodicals, Inc.

A novel gamma-methylidene-spirobutanolide spirolephtoshol (1) was isolated from ascomycetous fungus Leptosphaeria doliolum as a cytotoxic compound. The relative structure was established by the NMR analysis involving the NOE experiments. Absolute structure of the bicyclic moiety was determined by chemical derivation followed by the CD analysis. The relative and absolute stereochemistry of the side chain was established by comparison of the (1)H NMR spectra and the chiral GC chromatograms of the degradation product with the synthetic samples.

Plectranthus scutellarioides (synonym: Coleus blumei ) is a popular garden plant, cultivated worldwide and is known to be infected with several viroids of the genus Coleviroid , family Pospiviroidae . Coleus blumei viroid 1 (CbVd-1) is the…

Dahlia (Asteraceae) has been cultivated since 1841 in Japan. Two viroids belonging to the family Pospiviroidae , Potato spindle tuber viroid (PSTVd) and Dahlia latent viroid (DLVd), were identified separately from dahlia plants in Japan and…