Grafting the Way to the Systemic Silencing Signal in Plants

Grafting is a powerful but complex means to study the spread of RNA silencin

Light intensity affects RNA silencing of a transgene in Nicotiana benthamiana plants

Abstract Background Expression of exogenous sequences in plants is often suppressed through one of the earliest described RNA silencing pathways, sense post-transcriptional gene silencing (S-PTGS). This type of suppression has made significant contributions to our knowledge of the biology of RNA silencing pathways and has important consequences in plant transgenesis applications. Although significant progress has been made in recent years, factors affecting the stability of transgene expression are still not well understood. It has been shown before that the efficiency of RNA silencing in plants is influenced by various environmental factors. Results Here we report that a major environmental factor, light intensity, significantly affects the induction and systemic spread of S-PTGS. Moreover, we show that photoadaptation to high or low light intensity conditions differentially affects mRNA levels of major components of the RNA silencing machinery. Conclusions Light intensity is one of the previously unknown factors that affect transgene stability at the post-transcriptional level. Our findings demonstrate an example of how environmental conditions could affect RNA silencing.</p

PSTVd infection in Nicotiana benthamiana plants has a minor yet detectable effect on CG methylation

Viroids are small circular RNAs infecting a wide range of plants. They do not code for any protein or peptide and therefore rely on their structure for their biological cycle. Observed phenotypes of viroid infected plants are thought to occur through changes at the transcriptional/translational level of the host. A mechanism involved in such changes is RNA-directed DNA methylation (RdDM). Till today, there are contradictory works about viroids interference of RdDM. In this study, we investigated the epigenetic effect of viroid infection in Nicotiana benthamiana plants. Using potato spindle tuber viroid (PSTVd) as the triggering pathogen and via bioinformatic analyses, we identified endogenous gene promoters and transposable elements targeted by 24 nt host siRNAs that differentially accumulated in PSTVd-infected and healthy plants. The methylation status of these targets was evaluated following digestion with methylation-sensitive restriction enzymes coupled with PCR amplification, and bisulfite sequencing. In addition, we used Methylation Sensitive Amplification Polymorphism (MSAP) followed by sequencing (MSAP-seq) to study genomic DNA methylation of 5-methylcytosine (5mC) in CG sites upon viroid infection. In this study we identified a limited number of target loci differentially methylated upon PSTVd infection. These results enhance our understanding of the epigenetic host changes as a result of pospiviroid infection

Dicer-like 4 is involved in restricting the systemic movement of Zucchini yellow mosaic virus in Nicotiana benthamiana

[EN] Zucchini yellow mosaic virus (ZYMV) induces serious diseases in cucurbits. To create a tool to screen for resistance genes, we cloned a wild ZYMV isolate and inserted the visual marker Roseal to obtain recombinant clone ZYMV-Rosl. While in some plant-virus combinations Roseal induces accumulation of anthocyanins in infected tissues, ZYMV-Rosl infection of cucurbits did not lead to detectable anthocyanin accumulation. However, the recombinant virus did induce dark red pigmen-tation in infected tissues of the model plant Nicotiana ben-thamiana. In this species, ZYMV-Rosl multiplied efficiently in local inoculated tissue but only a few progeny particles estab-lished infection foci in upper leaves. We used this system to analyze the roles of Dicer-like (DCL) genes, core components of plant antiviral RNA silencing pathways, in ZYMV infection. ZYMV-Rosl local replication was not significantly affected in single DCL knockdown lines nor in double DCL2/4 and triple DCL2/3/4 knockdown lines. ZYMV-Rosl systemic accumula-tion was not affected in knockdown lines DCL1, DCL2, and DCL3. However in DCL4 and also in DCL2/4 and DCL2/3/4 knockdown lines, ZYMV-Rosl systemic accumulation dra-matically increased, which highlights the key role of DCL4 in restricting virus systemic movement. The effect of DCL4 on ZYMV systemic movement was confirmed with a wild-type version of the virus.We thank V. Aragones for excellent technical assistance. This work was supported by the Spanish Ministerio de Economia y Competitividad (MINECO) through grants BI02014-54269-R and AGL2013-49919-EXP and by the Greek Ministry for Education and Religious Affairs (Program Aristeia II, 4499, ViroidmiR; ESPA 2007-2013). A. Carbonell was supported by an Individual Fellowship from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 655841.Cordero-Cucart, MT.; Cerdán García, L.; Carbonell Olivares, A.; Katsarou, K.; Kalantidis, K.; Daros Arnau, JA. (2016). Dicer-like 4 is involved in restricting the systemic movement of Zucchini yellow mosaic virus in Nicotiana benthamiana. Molecular Plant-Microbe Interactions. 30(1):63-71. https://doi.org/10.1094/MPMI-11-16-0239-RS637130

Prediction of novel microRNA genes in cancer-associated genomic regions—a combined computational and experimental approach

The majority of existing computational tools rely on sequence homology and/or structural similarity to identify novel microRNA (miRNA) genes. Recently supervised algorithms are utilized to address this problem, taking into account sequence, structure and comparative genomics information. In most of these studies miRNA gene predictions are rarely supported by experimental evidence and prediction accuracy remains uncertain. In this work we present a new computational tool (SSCprofiler) utilizing a probabilistic method based on Profile Hidden Markov Models to predict novel miRNA precursors. Via the simultaneous integration of biological features such as sequence, structure and conservation, SSCprofiler achieves a performance accuracy of 88.95% sensitivity and 84.16% specificity on a large set of human miRNA genes. The trained classifier is used to identify novel miRNA gene candidates located within cancer-associated genomic regions and rank the resulting predictions using expression information from a full genome tiling array. Finally, four of the top scoring predictions are verified experimentally using northern blot analysis. Our work combines both analytical and experimental techniques to show that SSCprofiler is a highly accurate tool which can be used to identify novel miRNA gene candidates in the human genome. SSCprofiler is freely available as a web service at http://www.imbb.forth.gr/SSCprofiler.html

Insight on genes affecting tuber development in potato upon <i>Potato spindle tuber viroid</i> (PSTVd) infection

Potato (Solanum tuberosum L) is a natural host of Potato spindle tuber viroid (PSTVd) which can cause characteristic symptoms on developing plants including stunting phenotype and distortion of leaves and tubers. PSTVd is the type species of the family Pospiviroidae, and can replicate in the nucleus and move systemically throughout the plant. It is not well understood how the viroid can affect host genes for successful invasion and which genes show altered expression levels upon infection. Our primary focus in this study is the identification of genes which can affect tuber formation since viroid infection can strongly influence tuber development and especially tuber shape. In this study, we used a large-scale method to identify differentially expressed genes in potato. We have identified defence, stress and sugar metabolism related genes having altered expression levels upon infection. Additionally, hormone pathway related genes showed significant up- or down-regulation. DWARF1/DIMINUTO, Gibberellin 7-oxidase and BEL5 transcripts were identified and validated showing differential expression in viroid infected tissues. Our study suggests that gibberellin and brassinosteroid pathways have a possible role in tuber development upon PSTVd infection

Chromatin dynamics during interphase and cell division:similarities and differences between model and crop plants

Genetic information in the cell nucleus controls organismal development, responses to the environment and finally ensures own transmission to the next generations. To achieve so many different tasks, the genetic information is associated with structural and regulatory proteins, which orchestrate nuclear functions in time and space. Furthermore, plant life strategies require chromatin plasticity to allow a rapid adaptation to abiotic and biotic stresses. Here, we summarize current knowledge on the organisation of plant chromatin and dynamics of chromosomes during interphase and mitotic and meiotic cell divisions for model and crop plants differing as to the genome size, ploidy and amount of genomic resources available. The existing data indicate that chromatin changes accompany most (if not all) cellular processes and that there are both shared and unique themes in the chromatin structure and global chromosome dynamics among species. Ongoing efforts to understand the molecular mechanisms involved in chromatin organisation and remodeling have, together with the latest genome editing tools, potential to unlock crop genomes for innovative breeding strategies and improvements of various traits

Kriton Kalantidis introduces the fascinating biology of Virioids, smallest-known pathogens.

As part of the INDEPTH Academy Kriton Kalantidis from the University of Crete introduces the fascinating biology of viroids (the smallest known infectious pathogens) and their interaction with the plant nucleus