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Signal transduction pathways regulating morphogenesis in Colletotrichum trifolii and Sclerotinia sclerotiorum

Changbin Chen, University of Nebraska - Lincoln

Abstract

Fungal morphogenesis is a key component of host invasion. Pathogenic development of fungi requires perception of the environment and response to appropriate cues, which triggers signaling pathways that eventually modulate genes expression leading to the desired cellular responses. The goal of my research is to explore the molecular events regulating fungal morphogenesis, with particular emphasis on the response pathways specifying hyphal growth in Colletotrichum trifolii and sclerotial development in Sclerotinia sclerotiorum. A major focus of this project is to identify and characterize the important signaling molecules that control fungal morphogenesis by comparison to functionally equivalent mammalian proteins, based on the assumption that similar signal transduction pathways exist in both. Thus, several important genes and their related signaling pathways were investigated, including TB3 kinase and two small GTPases (Ct-Ras and Ct-Rac1) in C. trifolii and a MAP kinase (smk1) gene in S. sclerotiorum. ^ Our evidence has demonstrated that C. trifolii TB3 kinase, a functional homologue of Neurospora crassa COT1, may be positioned in a signaling cascade regulating proper hyphal morphology by functioning as a transcription factor. We also characterized the role of small GTPases in fungal morphogenesis. Previous studies have shown that an “oncogenic” Ras (DARas), when expressed in C. trifolii , exhibited aberrant hyphal growth and differentiation under nutrient deprivation conditions. We found that Rac is a downstream effector of Ras and regulates proper hyphal morphology via two distinct signaling pathways (MAPK activation and ROS generation). Finally, we established a novel model to explain the observation that proline reverts the DARas phenotype in minimal media. Proline acts as a potent antioxidant to scavenge ROS generation induced by DARas and therefore inhibits ROS-dependent apoptosis. ^ Additionally, we investigated the role of an ERK-type MAPK homologue (smk1) in sclerotial development in S. sclerotiorum . Inhibition of MAPK severely interferes with hyphal growth and sclerotial maturation. Our findings demonstrate that Smk1 functions to regulate sclerotial development through interconnection with pH-dependent and cAMP-dependent pathways. Importantly, the Ras/MAPK pathway is necessary for sclerotial development and is tightly regulated by a PKA-independent cAMP signaling pathway. Our data suggest the cross-talk between these two pathways is controlled, at least in part by the small GTPase Rap-1. ^

Subject Area

Biology, Molecular|Agriculture, Plant Pathology

Recommended Citation

Chen, Changbin, "Signal transduction pathways regulating morphogenesis in Colletotrichum trifolii and Sclerotinia sclerotiorum" (2004). ETD collection for University of Nebraska - Lincoln. AAI3142074.
http://digitalcommons.unl.edu/dissertations/AAI3142074

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