Defining the regulatory network that governs effector gene expression during plant infection by the blast fungus Magnaporthe oryzae

Molinari, Camilla (2025) Defining the regulatory network that governs effector gene expression during plant infection by the blast fungus Magnaporthe oryzae. Doctoral thesis, University of East Anglia.

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Abstract

Rice blast disease, caused by the filamentous fungus Magnaporthe oryzae, threatens global rice production. To invade the host plant, the fungus secretes a battery of effector proteins with distinct functions and subcellular targets. In M. oryzae, effector-encoding genes are subject to strict spatiotemporal regulation that aligns with disease progression. However, our understanding of infection-related transcriptional control remains limited in plant pathogenic fungi. This thesis explores effector gene regulation in M. oryzae through two complementary approaches: a forward genetic screen to identify novel regulatory components and a reverse genetic strategy to enhance our understanding of established regulatory pathways. The forward screen is based on the hypothesis that most effector genes are only expressed in the host plant and require transcriptional regulation for this expression profile. By mutagenesis of MEP3-GFP strains, I isolated three putative constitutive effector regulator (CER) mutants showing constitutive MEP3-GFP expression. Analysis of the CER mutants identified the G-protein regulator RGS1, previously reported to repress late expression effectors in M. oryzae prior to plant infection. This finding, consistent with earlier research, provides new insight into the regulatory role of RGS1 and its broader function in infection-related transcriptional networks. This prompted the second approach, in which we demonstrate that the transcription factor Bip1 (B-ZIP Involved in Pathogenesis-1) is a component of the conserved Pmk1 MAPK /Mst12 signalling pathway—essential for appressorium formation, penetration, and invasive growth. Global transcriptome analysis revealed Bip1 and Mst12 co-regulate a common subset of genes, including effectors, during pathogenesis. Furthermore, Bip1 is phosphorylated during plant infection in a Pmk1-dependent manner, BIP1 expression is Mst12-dependent, and it physically interacts with Mst12, suggesting heterodimer formation. These findings support a model in which Bip1 and Mst12 are components of a hierarchy of co-ordinately controlled transcription factors that regulate M. oryzae pathogenesis, offering new mechanistic insights into fungal virulence.

Item Type:	Thesis (Doctoral)
Faculty \ School:	Faculty of Science > School of Biological Sciences
Depositing User:	Chris White
Date Deposited:	07 Jul 2025 10:46
Last Modified:	07 Jul 2025 10:46
URI:	https://ueaeprints.uea.ac.uk/id/eprint/99849
DOI:

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