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Viroids: unusual small pathogenic RNAs

100%

Gora-Sochacka A.

Acta Biochimica Polonica

2004

tom 51

nr 3

Viroids are small (about 300 nucleotides), single-stranded, circular, non-en- capsidated pathogenic RNA molecules. They do not code for proteins and thus depend on plant host enzymes for their replication and other functions. They induce plant diseases by direct interaction with host factors but the mechanism of pathogenicity is still unknown. They can alter the expression of selected plant genes important for growth and development. Viroids belong to two families, the Avsunviroidae and the Pospiviroidae. Viroids of the Avsunviroidae family adopt a branched or quasi rod-like secondary structure in their native state. Members of the Pospiviroidae family adopt a rod-like secondary structure. In such native structures five structural/functional domains have been identified: central (C), pathogenicity, variable and two terminal domains. The central conserved region (CCR) within the C domain characterizes viroids of the Pospiviroidae. Specific secondary structures of this region play an important role in viroid replication and processing. Viroids of the Avsunviroidae family lack a CCR but possess self-cleaving properties by forming hammerhead ribozyme structures; they accumulate and replicate in chloroplasts, whereas members of the Pospiviroidae family have a nuclear localization. Viroid replication occurs via a rolling circle mechanism using either a symmetric or asymmetric pathway in three steps, RNA transcription, processing and ligation.

Wykorzystanie systemów roślinnych do produkcji rekombinowanych cytokin

51%

Gora-Sochacka A. , Redkiewicz P. , Napiorkowska B. , Sirko A.

nr 1

Co-inoculation with two non-infectious cDNA copies of potato spindle tuber viroid [PSTVd] leads to the appearance of novel fully infectious variants

51%

Podstolski W. , Gora-Sochacka A. , Zagorski W.

nr 1

Potato spindle tuber viroid (PSTVd) is one of the smallest (about 360 nt) infectious plant agents. It is composed of a single-stranded circular non-coding RNA molecule. In the course of previous passage experiments with two intermediate PSTVd variants I2 and I4, three non-infectious clones (I2-50, I4-37 and I4 VI-17) were found. When inoculated separately as cDNAs on tomato “Rutgers” test plants these variants did not induce any visible disease symptoms and did not produce progeny. The presence of such non-infectious variants raises several questions about their origin and biology and to answer them, mixed co-infections with cDNA copies of two non-infectious variants (I2-50, I4-37) were performed. PSTVd infection was observed in seven out of 30 inoculated plants. The progeny isolated from three separate plants contained novel variants, together with the parental I2 and I4 sequences. It is conceivable that the appearance of repaired PSTVd molecules, clearly capable of cell-to-cell movement leading to the systemic infection, results from recombination events. An analysis of the recombinant molecules and comparison with databases identified the specific sites responsible for the restricted infectivity of the I2-50 and I4-37 PSTVd variants. In parallel experiments in which (+) strand PSTVd infectious transcripts were used, no recombinants were observed, and the original I2-50 and I4-37 non-infectious sequences were not detected in the progeny.

Antibody response to DNA vaccine against H5N1 avian influenza virus in broilers immunized according to three schedules

45%

Stachyra A. , Gora-Sochacka A. , Zagorski-Ostoja W. , Krol E. , Sirko A.

tom 61

nr 3