Computational screening and biochemical analyses have identified a range of substances that selectively inhibit phosphoenolpyruvate carboxylase (PEPC), a key enzyme of the C4 photosynthetic pathway, which is used for carbon fixation and biomass increase in many of the world’s worst weeds. In contrast, many of the most important crop plants use C3 photosynthesis. The selected substances belonging to the classes of chalcones, flavonoids, quinoxalines, stilbenes, or chemical derivatives thereof were tested for their affinity, selectivity, and binding mode at C3 and C4 isoforms of the enzyme as well as for their toxicity on typical soil bacteria and their inhibitory effect on photosynthesis, plant growth, and development in typical C3 and C4 plants. Substances belonging to the chalcone family showed the most pronounced effects in these studies. Depending on the number and position of hydroxyl substituents these substances show potent inhibition against C4 PEPC from Flaveria trinervia and weaker inhibition against C3 PEPC from Flaveria pringlei. Among the tested chalcones, okanin (2',3',4',3,4-Pentahydroxychalcone), found in the flowering plant Bidens pilosa, is the best C4 PEPC inhibitor with 5-fold selectivity on C4 over C3 PEPC. Binding measurements indicate that the compound binds to PEPC at the same binding pocket as the natural feed-back inhibitors of the C4 pathway, aspartate or malate. Growth of the soil bacteria Bacillus subtilis, Corynebacterium glutamicum, and Pseudomonas putida and of the gut bacterium Escherichia coli was not affected by this compound. Some of the other chalcones tested showed effects on some of the soil bacteria, but usually only at concentrations 10-fold above the IC50 for the C4 PEPC. 2',5'-dihydroxychalcone completely inhibited growth of the Gram-positives in minimal medium at 10-fold IC50. A screening assay on leaf disc level based on chlorophyll fluorescence measurements was established, which made it possible to rapidly screen in planta all of the compounds identified in the computational and biochemical screening experiments that are only available in small quantities. When studied on a whole plant level, okanin and another polyhydroxy chalcone derivative showed pronounced growth-inhibitory effects on the C4 weed Amaranthus retroflexus. There were no measurable effects on oilseed rape, a C3 plant, indicating selectivity. Hyperspectral imaging of the plants revealed altered photosystem efficiency and pigment composition.
Participating Core Groups
Prof. Dr. G. Groth, Biochemische Pflanzenphysiologie, HHU Düsseldorf
Prof. Dr. H. Gohlke, Pharmazeutische und Medizinische Chemie, HHU Düsseldorf
Prof. Dr. M. Bott and Dr. Melanie Brocker, IBG-1: Systemische Mikrobiologie, FZ Jülich
Dr. Fabio Fiorani, IBG-2 Pflanzenwissenschaften: Jülich Plant Phenotyping Centre, FZ Jülich
Prof. Dr. G. Groth
Tel: +49 (0)211 / 81 - 12822
Fax: +49 (0)211 / 81 - 13569
01.01.2014 – 31.12.2015
The total budget of C4-PSH is € 775.772. C4-PSH is part of the NRW-Strategieprojekt BioSC and thus funded by the Ministry of Innovation, Science and Research of the German State of North Rhine-Westphalia.
Nguyen, GT, Erlenkamp, G, Jack, O, Kuberl, A, Bott, M, Fiorani, F, Gohlke, H and Groth, G (2016). Chalcone-based selective inhibitors of a c4 plant key enzyme as novel potential herbicides. Sci Rep 6: 27333.
Paulus, JK, Forster, K and Groth, G (2014). Direct and selective small-molecule inhibition of photosynthetic pep carboxylase: New approach to combat c4 weeds in arable crops. FEBS Lett 588(12): 2101-2106.