RA6 THESIS: Structure and function of A. ...

The structure and function of effector proteins expressed by Austropuccinia psidii in the early stages of myrtle rust infection

2021

Johns T. 2021. The structure and function of effector proteins expressed by Austropuccinia psidii in the early stages of myrtle rust infection. Unpublished Honours thesis, University of Canterbury. 46 p.

NOTE

This thesis has been rewritten in a manuscript format and co-authored by Grant Smith, Rebekah Frampton, Falk Kalamorz, Michael Currie, Jenna Gilkes, Claudia Meisrimler and Renwick Dobson.

ABSTRACT

Myrtle rust disease, caused by the fungal rust pathogen Austropuccinia psidii, has been known to infect a wide range of Myrtaceae hosts. In Australia, the disease has caused the population of Myrtaceae plants to decline, and threatens to do the same to beloved New Zealand natives. Despite the large host range of A. psidii, many aspects about the infection process are still unknown. It is hypothesised that like many other pathogens, effector proteins play a significant role in establishing a successful infection in the host. This research reports the identification of five novel A. psidii effector proteins that are predicted to be essential in the establishment of myrtle rust infection. These effector proteins are the first to be studied from A. psidii. Structural features were identified on A. psidii effector candidates using bioinformatics and analytical methods. Bioinformatics show that two of these proteins are similar to fungal cellulase and xyloglucanase enzymes. One effector protein, AP1260 was successfully expressed and purified by recombinant expression in E. coli cells. AP1260 is a monodisperse protein as shown by analytical ultracentrifugation experiments and contains secondary structures as shown by circular dichroism. Emphasis was put on obtaining X-ray crystallography data on AP1260 to probe its biochemical function in myrtle rust infection, however further crystallography screening is required. Understanding the structure and mode of action of these effectors is crucial in order to provide insight into the establishment and progression of myrtle rust. Therefore, it is crucial to further probe these effectors as they are potential targets for a disease management strategy for myrtle rust disease.

KEYWORDS

Bioinformatics; APSIP001; APSIP005; Effector; Proteins; SWISS-MODEL; AlphaFold2; X-ray crystallography; Enzymes; Homology