| Affiliation: | 1. School of Chemistry and Molecular Biosciences, Australian Infectious Diseases Research Centre and Institute for Molecular Bioscience, University of Queensland, Brisbane, QLD, 4072 Australia;2. School of Chemistry and Molecular Biosciences, Australian Infectious Diseases Research Centre and Institute for Molecular Bioscience, University of Queensland, Brisbane, QLD, 4072 Australia Division of Plant Sciences, Research School of Biology, Australian National University, Canberra, ACT, 2601 Australia;3. Commonwealth Scientific and Industrial Research Organisation Agriculture and Food, Canberra, ACT, 2601 Australia;4. RIKEN Center for Sustainable Resource Science, Yokohama, Kanagawa, 230-0045 Japan;5. Commonwealth Scientific and Industrial Research Organisation Agriculture and Food, Adelaide, SA, 5064 Australia;6. Australian Synchrotron, Macromolecular Crystallography, Clayton, Victoria, 3168 Australia;7. Division of Plant Sciences, Research School of Biology, Australian National University, Canberra, ACT, 2601 Australia |
| Abstract: | During infection, plant pathogens secrete effector proteins to facilitate colonization. In comparison with our knowledge of bacterial effectors, the current understanding of how fungal effectors function is limited. In this study, we show that the effector AvrL567-A from the flax rust fungus Melampsora lini interacts with a flax cytosolic cytokinin oxidase, LuCKX1.1, using both yeast two-hybrid and in planta bimolecular fluorescence assays. Purified LuCKX1.1 protein shows catalytic activity against both N6-(Δ2-isopentenyl)-adenine (2iP) and trans-zeatin (tZ) substrates. Incubation of LuCKX1.1 with AvrL567-A results in increased catalytic activity against both substrates. The crystal structure of LuCKX1.1 and docking studies with AvrL567-A indicate that the AvrL567 binding site involves a flexible surface-exposed region that surrounds the cytokinin substrate access site, which may explain its effect in modulating LuCKX1.1 activity. Expression of AvrL567-A in transgenic flax plants gave rise to an epinastic leaf phenotype consistent with hormonal effects, although no difference in overall cytokinin levels was observed. We propose that, during infection, plant pathogens may differentially modify the levels of extracellular and intracellular cytokinins. |
