Effects of camptothecin on the rice blast fungus Magnaporthe oryzae

Rice blast caused by Magnaporthe oryzae B. Couch is one of the most devastating diseases on rice. Camptothecin (CPT), which was primarily isolated from Camptotheca acuminata, is well-known for its anti-tumor activities, and is also developed as a potential biological pesticide. We previously investigated the anti-microbial activities of CPT against 11 fungi, 3 oomycetes, and 4 bacteria, and found that CPT was strongly effective against M. oryzae, indicating its potential as a lead for developing fungicide against rice blast. However, the anti-fungal effects of CPT on M. oryzae need further elucidation. In this study, the anti-fungal activities of CPT against M. oryzae were further investigated, which revealed that CPT was effective against M. oryzae both in vitro and in vivo. The transcriptome of M. oryzae was analyzed after CPT treatment, which showed that CPT had a strong inhibitory effect on 'translation' and 'carbohydrate metabolism/energy metabolism' of M. oryzae. Some physiology characteristics of M. oryzae were also assayed, which confirmed that CPT inhibited RNA synthesis, protein synthesis, and carbohydrate metabolism/energy metabolism of M. oryzae, and caused membrane damage. The molecular simulation result showed that CPT binds to the interface of DNA-topoisomerase I complex of M. oryzae. In conclusion, CPT is a promising lead for developing fungicide against rice blast. CPT may bind to DNA-topoisomerase I complex of M. oryzae, thus affecting 'translation' and 'carbohydrate metabolism/energy metabolism', leading to cell death.