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Guan X.,Karlsruhe Institute of Technology | Buchholz G.,AlPlanta Institute for Plant Research | Nick P.,Karlsruhe Institute of Technology
Journal of Experimental Botany

Plant innate immunity is composed of two layers. Basal immunity is triggered by pathogen-associated molecular patterns (PAMPs) such as the fagellin-peptide flg22 and is termed PAMP-triggered immunity (PTI). In addition, effector-triggered immunity (ETI) linked with programmed cell death and cytoskeletal reorganization can be induced by pathogen-derived factors, such as the Harpin proteins originating from phytopathogenic bacteria. To get insight into the link between cytoskeleton and PTI or ETI, this study followed the responses of actin flaments and microtubules to flg22 and HrpZ in vivo by spinning-disc confocal microscopy in GFP-tagged marker lines of tobacco BY-2. At a con-centration that clearly impairs mitosis, flg22 can induce only subtle cytoskeletal responses. In contrast, HrpZ causes a rapid and massive bundling of actin microflaments (completed in ∼20 min, i.e. almost simultaneously with extracellular alkalinization), which is followed by progressive disintegration of actin cables and cytoplasmic microtubules, a loss of cytoplasmic structure, and vacuolar disintegration. Cytoskeletal disruption is proposed as an early event that discriminates HrpZ-triggered ETI-like defence from flg22-triggered PTI. © The Author(s) [2013]. Source

Lamprecht R.L.,Stellenbosch University | Spaltman M.,Stellenbosch University | Stephan D.,Stellenbosch University | Wetzel T.,AlPlanta Institute for Plant Research | Burger J.T.,Stellenbosch University

The complete sequences of RNA1, RNA2 and satellite RNA have been determined for a South African isolate of Grapevine fanleaf virus (GFLV-SACH44). The two RNAs of GFLV-SACH44 are 7,341 nucleotides (nt) and 3,816 nt in length, respectively, and its satellite RNA (satRNA) is 1,104 nt in length, all excluding the poly(A) tail. Multiple sequence alignment of these sequences showed that GFLV-SACH44 RNA1 and RNA2 were the closest to the South African isolate, GFLV-SAPCS3 (98.2% and 98.6% nt identity, respectively), followed by the French isolate, GFLV-F13 (87.3% and 90.1% nt identity, respectively). Interestingly, the GFLV-SACH44 satRNA is more similar to three Arabis mosaic virus satRNAs (85%-87.4% nt identity) than to the satRNA of GFLV-F13 (81.8% nt identity) and was most distantly related to the satRNA of GFLV-R2 (71.0% nt identity). Full-length infectious clones of GFLV-SACH44 satRNA were constructed. The infectivity of the clones was tested with three nepovirus isolates, GFLV-NW, Arabis mosaic virus (ArMV)-NW and GFLV-SAPCS3. The clones were mechanically inoculated in Chenopodium quinoa and were infectious when co-inoculated with the two GFLV helper viruses, but not when co-inoculated with ArMV-NW. © 2013 by the authors; licensee MDPI, Basel, Switzerland. Source

Jarausch B.,AlPlanta Institute for Plant Research | Jarausch W.,AlPlanta Institute for Plant Research
Journal of Pest Science

The univoltine psyllid Cacopsylla picta (Foerster) is the main vector of 'Ca. Phytoplasma mali' in Germany, the causal agent of apple proliferation, an economically important disease of apple in Europe. Its population dynamics on its host plant apple (Malus spp.) and migration to coniferous shelter plants for overwintering have been described for Southwest Germany. Temporary greenhouse rearing under controlled conditions, starting from field-collected overwintered adults, was set up to produce homogeneous offspring. New generation adults were transferred to conifers in the greenhouse at the beginning of the natural migration phase to obtain a continuous rearing spanning the aestivation and hibernation period. However, efforts to directly overwinter C. picta on different conifer species failed. The natural overwintering sites were therefore identified and their climatic conditions, mainly moderate summer temperatures with increased humidity and natural cold winter conditions including frost were reproduced. Teneral individuals of the new generation did not switch instantaneously from host plants to conifers. Successful overwintering under experimental conditions was only achieved using a gradual host plant transfer. By incorporating these key factors two continuous rearings of C. picta were maintained over 3 years with both, spruce and pine, as suitable shelter plants. This is the first report of a permanent rearing of C. picta under experimental conditions. Our data show experimentally that C. picta is univoltine and that conifers act only as shelter plants for overwintering and not as hosts for reproduction. © 2014 Springer-Verlag Berlin Heidelberg. Source

Marcone C.,University of Salerno | Jarausch B.,AlPlanta Institute for Plant Research | Jarausch W.,AlPlanta Institute for Plant Research
Journal of Plant Pathology

'Candidatus Phytoplasma prunorum' is an important prokaryotic pathogen that infects stone fruits in Europe. It is known to cause several economically relevant disorders of Prunus spp. which are collectively referred to as European stone fruit yellows (ESFY). This organism is phylogenetically closely related to other important fruit trees pathogens such as apple proliferation (AP), pear decline (PD) and peach yellow leaf roll (PYLR) agents. Together they form a distinct phylogenetic cluster, the AP or 16SrX group. Like the other fruit tree phytoplasmas of the AP group, 'Ca. P. prunorum' exhibits a high host specificity. In nature, this pathogen has been reported to infect only plants in the genus Prunus and to be transmitted by one insect vector species, the psyllid (Psyllidae) Cacopsylla pruni. Also, 'Ca. P. prunorum' includes strains which greatly differ in virulence. This review summarizes the current knowledge of 'Ca. P. prunorum' with emphasis on advances that have been made during the last two decades in understanding molecular and epidemiological aspects. Prospects for disease management and future research which could provide insights into the largely unknown mechanisms involved in pathogenicity of 'Ca. P. prunorum', are also critically discussed. Source

Dalakouras A.,AlPlanta Institute for Plant Research | Wassenegger M.,AlPlanta Institute for Plant Research | Wassenegger M.,Center for Organismal Studies Heidelberg
RNA Biology

RNA-directed DNA methylation (RdDM) involves sequence-specific guiding of the de novo methylation machinery to complementary genomic DNA by RNA molecules. It is still elusive whether guide RNAs bind directly to DNA or to nascent transcripts produced from it. Even the nature of the guide RNAs is not elucidated. RNA interference (RNAi) studies provided a link between RNAi and RdDM indicating that small interfering RNAs (siRNAs) trigger and guide cytosine methylation. The "siRNA hypothesis" is generally accepted. However, recent data demonstrated that RdDM is not always associated with the accumulation of corresponding siRNAs. RdDM triggers may differ from guide RNAs and further studies are needed to clarify if guide RNAs are small or long RNAs, if they are single or double stranded and if they target DNA or nascent transcript. © 2013 Landes Bioscience. Source

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