AG Boch Research Focus
Bacterial plant pathogens and their weapons.
Two organisms fight to survive. The prokaryote aims to acquire nutrients whereas the eukaryote aims to protects the integrity of its cells.
Plants are well able to defende themselves and only specialized pathogens can colonize them. These pathogens have evolved sophisticated molecular weapons. Pseudomonas syringae and Xanthomonas bacteria use a type III secretion system (T3SS) to inject ca. 30 different effector proteins into plant cells (Fig. 1). These effectors sabotage the host cell from within (Fig. 2) and we study their molecular activities.
Fig. 1: Electron microscopy picture of a bacterial cell with type III secretion system and secreted effectors. Picture by Ian Brown. Healthy and infected Arabidopsis thaliana leaves are shown below.
|Fig.2: Plant cells under attack. (1) Bacterial effector proteins (blue ball) are injected via a type III secretion system (red) into plant cells. (2) Inside the cell, effectors interact with host components and travel to subcellular locations. (3) TALEs from Xanthomonas bind to promoters inside the plant nucleus and induce expression of plant genes.|
TALEs (transcription activator-like effectors) from rice-pathogenic Xanthomonas oryzae induce plant SWEET sugar exporters (Fig. 3). X. oryzae strains can harbour up to 26 different TALEs and we explore which plant genes are targeted.
|Fig. 3: TALEs are molecular gene switches. Different TALEs induce the rice OsSWEET14 gene. The bacteria spread through the rice leaf veins and cause water-soaked lesions (black arrow).|
We have cracked the code how TALEs recognize DNA-sequences. They bind DNA via a central repeat domain. Each repeat recognizes one bp via two amino acids (called RVD) (Fig. 4). Different RVDs recognize different bases and different TALEs contain different arrangements of repeats. This modularity has been a breakthrough for biotechnology, because it allows to design artificial proteins with any desired DNA-binding specificity.
|Fig. 4: DNA-binding specificity of TALEs. Each 34-amino acid-repeat binds to one DNA bp and the amino acids at position 12 and 13 in each repeat determine specificity.|
Genome editing is a technique to specifically modify any sequence in a eukaryotic cell. This method holds great prospects for targeted breeding in agriculture and livestock, personalized medicine, and a cure to heritable genetic disorders in humans.
TALENs (TALE-nuclease fusions) and CRISPR/Cas (Fig. 5) are very recently developed tools that have heralded a new age for genome editing with worldwide interest. We explore these techniques to develop plants with elevated pathogen resistance and other beneficial traits.
|Fig. 5: TALEN and CRISPR/Cas are key tools for genome editing.|
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Jackson, R.W., Mansfield, J.W., Ammouneh, H., Dutton, L.C., Wharton, B., Ortiz-Barredo, A., Arnold, D.L., Tsiamis, G., Sesma, A., Butcher, D., Boch, J., Kim, Y.J., Martin, G.B., Tegli, S., Murillo, J., and Vivian, A. (2002): Location and activity of members of a family of virPphA homologues in pathovars of Pseudomonas syringae and P. savastanoi. , Mol. Plant Pathol. 3, 205-216. weitere Informationen