Abstract - To better understand regulation for expressions of fungal effector genes, in this study, I conducted experiments on isolating the key regulators for two important necrotrophic effectors in Parastagonospora nodorum. Parastagonospora nodorum (P. nodorum) is an important necrotrophic fungus on wheat causing enormous yield losses in Australia per annum. A well-known infection strategy in this fungus is secreting necrotrophic effectors into the wheat cell and causes necrosis on the wheat leaves. Two of the necroptrophic effectors are named ToxA and Tox3. The past studies have been focusing on the interactions between the plant proteins and necrotrophic effectors. However, how these effectors are regulated and expressed is largely unclear.
In this research, it was indicated that nutrient sources such as ammonium and nitrate could trigger or suppress Tox3 expression in vitro; on the contrary, ToxA expression was not affected by nutrients. Surprisingly, ToxA expression was extremely low in vitro; however, showed consistent and strong expression after replacing the ToxA gene with GFP. This implied that expression of ToxA might be dependent on post-transcriptional regulation.
Also, an important cis-regulatory element (Tox3BS) for Tox3 expression was discovered in this study. A putative C2H2 zinc finger transcription factor PnCon7 was found to bind to Tox3BS and regulated Tox3 expression. Interestingly, PnCon7 was alternatively spliced into 4 variants in P. nodorum and therefore produced 4 proteins with different structures. Nevertheless, only 3 variants were identified to specifically interact with the Tox3 promoter. The dynamic existence of these variants revealed that alternative splicing of PnCon7 was associated with fungal adaptation. Silencing of PnCon7 showed dose-dependent down-regulation of Tox3 expression and expressions of genes with the putative Tox3BS. Moreover, PnCon7 silenced transformants were less pathogenic on the Tox3 sensitive wheat plants. Surprisingly, expressions of two other necrotrophic effector genes ToxA and Tox1 were also down-regulated in those transformants.
In this talk, I am going to show several important and novel findings: 1. P. nodorum senses nutrients and triggers or suppresses Tox3 expression; 2. ToxA expression is not largely dependent on nutrients or transcription initiation; 3. PnCon7 binds to Tox3BS and regulates Tox3 expression; 4. Alternative splicing is related with fungal adaptation in different environment.
Biography - Shao-Yu completed a Bachelor degree in Plant Pathology in 2008 at National Taiwan University then moved to Japan to pursue a Master degree in 2009 at Kyoto University. During her study at Kyoto University, she worked on isolating important effectors for the anthracnose fungus Colletotrichum orbiculare. She joined Peter Solomon's lab to conduct her PhD study in 2013. Her work involved in deciphering the transcriptional regulation of necrotrophic effector genes and disease development in plant pathogenic fungus Parastagonospora nodorum.