Investigating Natural Products involved in Avirulence Signalling between Rice and the Fungal Rice Blast Pathogen Magnaporthe oryzae
Organic Molecular Chemistry - Synthesis and Characterisation
Metabolism, Biochemistry and Genetics of Microorganisms
Final Report Abstract
Fungi are ubiquitous organisms in the environment. They interact with plants, animals and other organisms and sometimes cause diseases, especially in plants. These diseases can cause significant harm in crop plants such as rice. Major rice diseases are caused by fungi of the Magnaporthe family including M. grisea and M. oryzae. Previous research has shown that resistance of some rice cultivars to fungal disease is mediated by small molecules known as natural products. In particular an unknown natural product produced by M. oryzae called ACE1 is known to stimulate resistance mechanisms in resistant rice cultivars. This project focused on attempts to determine the structure of ACE1 which could then be used as a new type of crop-protecting compound. The project demonstrated that ACE1 belongs to a class of fungal metabolites known as cytochalasins. Significant progress was made in determining the molecular precursors of the ACE1 compounds and many, but not all, of the chemical reactions which M. oryzae uses in its construction. Much new information has been gathered about the biochemical steps in the construction of the entire family of cytochalasins. These compounds often mediate disease processes, especially in plants, and the results of this project have enabled a much better understanding of how these compounds are made by fungi and the genetic control processes involved. Cytochalasins are compounds which also have significant effects on human cells. For example they are cytotoxic and can selectively kill cancer cells, but they are also toxic and cannot yet be used as medicines. This project has determined how cytochalasin molecules are made and allowed new versions to be designed and made using new biotechnology approaches. In addition we have devised the first methods for chemically modifying cytochalasins with useful marker molecules. This has allowed us to design compounds which can penetrate human cells and bind selectively to a molecule known as actin. Actin is involved in the division and reproduction of human cells, and is especially important in rapidly dividing cells such as those involved in cancer. Our new compounds should allow better methods for the study of these types of cells. We initially set out to use a fungal host known as Aspergillus oryzae for the expression of genes involved in the production of ACE1. In many previous studies this fungus had been shown to be a very reliable host organism. In this study we showed that A. oryzae possesses enzymes which can block the production of cytochalasins and prevent the successful production of these compounds. However we have now identified the gene and enzyme responsible for this behavior. We are now working on methods to remove (knockout) the gene in order to make a better A. oryzae host organism.
Publications
- Function of pathway specific regulators in the ACE1 and pyrichalasin H biosynthetic gene clusters, RSC Adv, 2019, 9, 35797–35802
V. Hantke, C. Wang, E. J. Skellam and R. J. Cox
(See online at https://doi.org/10.1039/c9ra07028a) - Investigating the Function of Cryptic Cytochalasan Cytochrome P450 Monooxygenases Using Combinatorial Biosynthesis, Org. Lett., 2019, 21, 8756–8760
C. Wang, K. Becker, S. Pfütze, E. Kuhnert, M. Stadler, R. J. Cox and E. Skellam
(See online at https://doi.org/10.1021/acs.orglett.9b03372) - Targeted Gene Inactivations Expose Silent Cytochalasans in Magnaporthe grisea NI980, Org. Lett., 2019, 21, 4163–4167
C. Wang, V. Hantke, R. J. Cox and E. Skellam
(See online at https://doi.org/10.1021/acs.orglett.9b01344) - Evidence for enzyme catalysed intramolecular [4+2] Diels–Alder cyclization during the biosynthesis of pyrichalasin H, Chem. Commun., 2020, 56, 2925–2928
V. Hantke, E. J. Skellam and R. J. Cox
(See online at https://doi.org/10.1039/c9cc09590j)
