Oral Presentation Australian Society for Microbiology Annual Scientific Meeting 2019

Dissecting the dual functionality of the Tox3 effector protein from the wheat pathogen Parastagonospora nodorum (#24)

Yi-Chang Sung 1 , Megan Outram 1 , Simon Williams 1 , Peter S Solomon 1
  1. Australian National University, Canberra, ACT, Australia

It had long been thought that necrotrophic plant pathogenic fungi use a barrage of lytic enzymes to break down host cells releasing nutrients for growth. However, in recent years it has emerged that some necrotrophic fungi facilitate disease through a strict gene-for-gene mechanism as observed in biotrophic pathogens. For the wheat pathogen Parastagonospora nodorum, the basis of this host specific interaction is small cysteine-rich effector proteins secreted during infection (ToxA, Tox1 and Tox3). These effectors interact with specific dominant susceptibility genes in the host leading to a programmed cell death response and disease. However, whilst we now understand the requirement of these effector proteins for disease, their modes of action remain poorly understood.

To characterise these necrotrophic effectors, a search for potential host protein binding partners for the Tox3 effector was conducted. From this work, the wheat TaPR1-1 protein was validated through three independent approaches to interact with Tox3. Subsequent analysis confirmed that Tox3 was able to interact with most acidic and basic TaPR1 proteins in wheat, but not those harbouring a C-terminal extension. We have now generated high-resolution crystal structures of several PR-1 proteins as well Tox3 and are using these dissect the basis and function of this protein interaction.

In this talk I will present our latest findings on dissecting the dual functionality of the Tox3 effector protein. Together with its function in causing cell death through its interaction with Snn3, we demonstrate that Tox3 has an important role in mediating PR-1 defence signalling and is required for disease development. These data have not only significantly advanced our understanding of necrotrophic diseases, but also provided a rare insight into the function and mechanism of the enigmatic plant PR-1 proteins.