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Stromuling when stressed!

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Stromules are stroma-filled tubules, extruding from the plastid and surrounded by both envelope membranes, but so far, stromules remain enigmatic structures and their function unknown. Stromules can interconnect plastids and have been found to associate with the nucleus, endoplasmic reticulum, Golgi complex, plasma membrane, mitochondria and peroxisomes. This minireview briefly summarizes markers to visualize stromules, inducers of stromules and provides new data about plant virus induced stromules.
 Translation of viral proteins from subgenomic RNAs (sgRNAs) is a common strategy among positive-stranded RNA viruses. Unlike host mRNA, sgRNA of Potato leafroll virus (PLRV) does not possess a cap at its 5' end nor a poly(A) tail at the 3' terminus, both of which are known to be crucial for translation of RNA in eukaryotic cells. Here, we demonstrate, that in wheat germ extract (WGE) truncation of the sgRNA1 5' UTR increases translation efficiency, as it has previously been observed in rabbit reticulocyte lysate (RRL), whereas removal of the 3' UTR does not affect translation. We also describe two regulatory elements located within the coding sequence of the coat protein (CP) gene and its read-through domain (RTD) and are responsible for regulation of in vitro translation of the PLRV sgRNA1. The first element is composed of the purine sequence AAAGGAAA located between the AUG codons of the CP and 17K genes. Deletion of this domain or its substitution by pyrimidines reduced by half the translation of both genes, whereas deletion of the RTD resulted in a 3.6-fold reduction in translation efficiency. This is the first report of translation regulatory elements of plant viruses located within a coding region.
Garlic virus A (GarV-A), Garlic virus B (GarV-B), Garlic virus C (GarV-C) and Garlic virus X (GarV-X) are members of the genus Allexivirus in the family Alphaflexiviridae. In this study, we collected 10, 30, 10 and 14 isolates of GarV-A, GarV-B, GarV-C and GarV-X, respectively, from different parts of Poland. All sequences of coat protein (CP) and nucleic-acid binding protein (NABP) regions of Allexivirus isolates available in GenBank were also included in this study. The nucleotide and amino acid sequences identities within each population differed substantially depending on the region of the genome and virus species. The results of selection pressure analysis showed that populations of each Allexivirus underwent negative selection, but the extent of the negative selection varied. It was also concluded that the GarV-A and GarV-C populations underwent a decrease in population size or balancing selection, while the GarV-B and GarV-X populations underwent an increase in population size. It was concluded that both populations of GarV-X evolved independently in each respective area, in contrast to populations of GarV-A, GarV-B and GarV-C.
Infectious transcripts play a key role in the research on plant viruses at the molecular level. A number of cDNA clones covering the whole genome of the Polish isolate of potato leafroll virus were constructed. Four overlapping clones were selected and assembled using restriction sites. The full copy was positioned between T7 RNA polymerase promoter and unique ScaI site. The full-length capped transcripts of the sequence of the viral genome synthesised in vitro were able to replicate in protoplasts and to produce the viral coat protein
The first demonstration on the aminoacylation capacity of the RNA genome of a plant virus appeared more than 25 years ago. Shortly thereafter, aminoacylation of the RNA genome of a number of other plant viruses was observed. This led to considerable work on the tRNA-like region of these viral RNAs, and to the first demonstration of the presence of pseudoknots in their folding pattern. In spite of the vast amount of efforts put into trying to understand the reason for the aminoacylation capacity of certain viral RNA genomes, as yet no clear general conclusion emerges. It rather looks as though the reason for aminoacylation may be different for different viruses, and that aminoacylation may operate at different levels in the virus life cycle. Given that certain RNA viruses possess structures which resemble that of tRNAs at their 5'- or 3'-termini, it is most likely that convergent evolution may have dominated the appearance of such structures in the virus world.
Viruses are known to be agents of important diseases of Insecta and Acarina, and many vertebrate and plant viruses have arthropods as propagative vectors. There is fossil evidence of arthropod pathogens for some micro-organisms, but not for viruses. Isolated virions would be hard to detect but, in fossil material, it could be easier to find traces of virus infection, mainly virus-induced cellular structures (VICS), easily recognisable by electron microscopy, such as virions encapsulated in protein occlusion bodies, aggregates of membrane-bounded virus particles and crystalline arrays of numerous virus particles. The following main taxa of viruses that multiply in arthropods are discussed both for some of their evolutionary aspects and for the VICS they cause in arthropods: A. dsDNA Poxviridae, Asfarviridae, Baculoviridae, Iridoviridae, Polydnaviridae and Ascoviridae, infecting mainly Lepidoptera, Hymenoptera, Coleoptera, Diptera and Acarina; B. ssDNA Parvoviridae, infecting mainly Diptera and Lepidoptera; C. dsRNA Reoviridae and Birnaviridae, infecting mainly Diptera, Hymenoptera and Acarina, and plant viruses also multiplying in Hemiptera; D. Amb.-ssRNA Bunyaviridae and Tenuivirus, that multiply in Diptera and Hemiptera (animal viruses) and in Thysanoptera and Hemiptera (plant viruses); E. -ssRNA Rhabdoviridae, multiplying in Diptera and Acarina (vertebrate viruses), and mainly in Hemiptera (plant viruses); F. +ssRNA Togaviridae, Nodaviridae, Tetraviridae, Flaviviridae and Picornaviridae, multiplying mainly in Lepidoptera, Hymenoptera, Diptera and Acarina (animal viruses), and in Hemiptera the plant Marafiviruses; G. RNA-RT Metaviridae and Pseudoviridae, multiplying in Diptera and Lepidoptera. Fossil arthropods included in amber or similar material derived from plant resins, that had the ultrastructure preserved, would be the best material for viral palaeontological studies. Volcanic ash and carbon deposits could also give good preservation.
Several different isolates of Tomato black ring virus (TBRV) have been collected in Poland from cucumber, tomato, potato and black locust plants. Biological tests showed some differences in the range of infected plants and the type of symptoms, which was the basis for selection of seven the most biologically different TBRV iso­lates. According to the sequence of TBRV-MJ, several primer pairs were designed and almost the entire sequence of both genomic RNAs was amplified. The RT-PCR products derived from all tested TBRV isolates were digested by restriction en­zymes. On the basis of the restriction patterns, the variable and the conserved re­gions of the TBRV genome were defined and the relationships between the Polish TBRV isolates established.
From Doronicum caucasicum plants exhibited chlorosis and/or mottling of leaves were isolated Cucumber mosaic virus (CMV) and Cherry leaf roll virus (CLRV). The identification was based on the biological and serological tests. Using ELISA test it was detected that more than 23% of Doronicum plants growing in Kraków and its surroundings was infected with CMV and only one plant was found to be infected with the complex of CMV/CLRV.
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