Phosphoenolpyruvate carboxylase (PEPC) and pyruvate phosphate dikinase (PPDK) are key enzymes of C4 photosynthesis. Both provide an excellent target for the development of effective weed control, as most troublesome weeds rely on C4 photosynthesis, while the majority of crops follow the classical C3 photosynthetic pathway. Our laboratory has identified potent, selective inhibitors targeting the C4 pathway based on high-resolution protein structures of PEPC and PPDK from the C4 model plant Flaveria trinervia.
High-throughput screening of purified C4 plant key enzymes revealed a number of small molecules as effective PPDK inhibitors, with IC50 values in the sub-µM and low µM range. Further studies on leaf tissues demonstrated that these compounds inhibit C4-driven photosynthesis in vivo, suggesting their potential as C4-specific herbicides. Similarly, pyrazolidine-3,5-diones emerged as a novel class of PEPC inhibitors with sub-µM inhibitory potential and no reported off-target effects.
Furthermore, chalcones, specifically natural products okanin and butein, were identified as selective C4 PEPC inhibitors, with IC50 values in the sub-µM and low µM range, respectively. These compounds bind at the same site as natural feedback inhibitors, offering a novel allosteric inhibition mode. They effectively suppressed the growth of the C4 weed Amaranthus retroflexus without affecting C3 plants or soil bacteria.
The development of these inhibitors addresses the challenge of weed resistance to conventional herbicides and the need for novel modes of action. By targeting the oligomeric state of C4 plant key enzymes with inhibitory peptides, we now aim to create biodegradable, C4-specific herbicides, ensuring food security in the face of climate change and evolving weed resistance. These findings pave the way for sustainable crop protection strategies that will minimize the environmental impact while maximizing agricultural productivity.