Unser 10. Leibniz Plant Biochemistry Symposium am 7. und 8. Mai war ein großer Erfolg. Thematisch ging es in diesem Jahr um neue Methoden und Forschungsansätze der Naturstoffchemie. Die exzellenten Vorträge über Wirkstoffe…
Omanische Heilpflanze im Fokus der Phytochemie IPB-Wissenschaftler und Partner aus Dhofar haben jüngst die omanische Heilpflanze Terminalia dhofarica unter die phytochemische Lupe genommen. Die Pflanze ist reich an…
Geschmack ist vorhersagbar: Mit FlavorMiner. FlavorMiner heißt das Tool, das IPB-Chemiker und Partner aus Kolumbien jüngst entwickelt haben. Das Programm kann, basierend auf maschinellem Lernen (KI), anhand der…
Genome editing by RNA-guided nucleases in model species is still hampered by low efficiencies, and isolation of transgene-free individuals often requires tedious PCR screening. Here, we present a toolkit that mitigates these drawbacks for Nicotiana benthamiana and Arabidopsis thaliana. The toolkit is based on an intron-optimized SpCas9-coding gene (zCas9i), which conveys dramatically enhanced editing efficiencies. The zCas9i gene is combined with remaining components of the genome editing system in recipient vectors, which lack only the user-defined guide RNA transcriptional units. Up to 32 guide RNA transcriptional units can be introduced to these recipients by a simple and PCR-free cloning strategy, with the choice of three different RNA polymerase III promoters for guide RNA expression. We developed new markers to aid transgene counter-selection in N. benthamiana, and demonstrate their efficacy for isolation of several genome-edited N. benthamiana lines. In Arabidopsis, we explore the limits of multiplexing by simultaneously targeting 12 genes by 24 sgRNAs. Perhaps surprisingly, the limiting factor in such higher order multiplexing applications is Cas9 availability, rather than recombination or silencing of repetitive sgRNA TU arrays. Through a combination of phenotypic screening and pooled amplicon sequencing, we identify transgene-free duodecuple mutant Arabidopsis plants directly in the T2 generation. This demonstrates high efficiency of the zCas9i gene, and reveals new perspectives for multiplexing to target gene families and to generate higher order mutants.
Publikation
Lee Erickson, J.; Ziegler, J.; Guevara, D.; Abel, S.; Klösgen, R. B.; Mathur, J.; Rothstein, S. J.; Schattat, M. H.;Agrobacterium-derived cytokinin influences plastid morphology and starch accumulation in Nicotiana benthamiana during transient assaysBMC Plant Biol.14127(2014)DOI: 10.1186/1471-2229-14-127
BackgroundAgrobacterium tumefaciens-based transient assays have become a common tool for answering questions related to protein localization and gene expression in a cellular context. The use of these assays assumes that the transiently transformed cells are observed under relatively authentic physiological conditions and maintain ‘normal’ sub-cellular behaviour. Although this premise is widely accepted, the question of whether cellular organization and organelle morphology is altered in Agrobacterium-infiltrated cells has not been examined in detail. The first indications of an altered sub-cellular environment came from our observation that a common laboratory strain, GV3101(pMP90), caused a drastic increase in stromule frequency. Stromules, or ‘stroma-filled-tubules’ emanate from the surface of plastids and are sensitive to a variety of biotic and abiotic stresses. Starting from this observation, the goal of our experiments was to further characterize the changes to the cell resulting from short-term bacterial infestation, and to identify the factor responsible for eliciting these changes.ResultsUsing a protocol typical of transient assays we evaluated the impact of GV3101(pMP90) infiltration on chloroplast behaviour and morphology in Nicotiana benthamiana. Our experiments confirmed that GV3101(pMP90) consistently induces stromules and alters plastid position relative to the nucleus. These effects were found to be the result of strain-dependant secretion of cytokinin and its accumulation in the plant tissue. Bacterial production of the hormone was found to be dependant on the presence of a trans-zeatin synthase gene (tzs) located on the Ti plasmid of GV3101(pMP90). Bacteria-derived cytokinins were also correlated with changes to both soluble sugar level and starch accumulation.ConclusionAlthough we have chosen to focus on how transient Agrobacterium infestation alters plastid based parameters, these changes to the morphology and position of a single organelle, combined with the measured increases in sugar and starch content, suggest global changes to cell physiology. This indicates that cells visualized during transient assays may not be as ‘normal’ as was previously assumed. Our results suggest that the impact of the bacteria can be minimized by choosing Agrobacterium strains devoid of the tzs gene, but that the alterations to sub-cellular organization and cell carbohydrate status cannot be completely avoided using this strategy.