Communication of Colletotrichum graminicola in development and pathogenic maize interactions
by Anina Yasmin Rudolph
Date of Examination:2024-10-23
Date of issue:2025-05-05
Advisor:Dr. Daniela Nordzieke
Referee:Dr. Daniela Nordzieke
Referee:Prof. Dr. Gerhard Braus
Persistent Address:
http://dx.doi.org/10.53846/goediss-11236
Files in this item
Name:Communication of Colletotrichum graminicola ...pdf
Size:54.1Mb
Format:PDF
This file will be freely accessible after 2025-10-21.
Abstract
English
Colletotrichum graminicola is a filamentous ascomycete that infects Zea mays and reduces the annual yield by 10-20 % worldwide. The fungus produces two asexual spore types, oval and falcate-shaped conidia of which the latter type is the main dispersal and infection propagule for above-ground infection. The role of oval conidia has not been described so far. However, it is known that oval but not falcate conidia undergo germling fusion. This study focuses on inter- and intraspecies communication of the fungal pathogen C. graminicola and is divided into three major projects. (I) The first project is about the interspecies interaction between C. graminicola and Zea mays and aimed to understand root recognition with a focus on differences in the infection strategies of oval and falcate conidia. Root infection experiments showed that oval- but not falcate conidia germinate in soil and grow chemotropically towards maize root-secreted exudates (MRE). Thereby, only oval conidia infect maize roots, spread to above-ground plant material, and cause stunting of maize plants. Within MRE the attractive signal resembles the diterpenoid 3β,15,16-trihydroxydolabrene (THD), which is secreted as part of the plant defense. MRE and diterpenoid sensing is mediated by CgSte3, a G-protein coupled receptor (GPCR). (II) The second project summarizes the signal recognition and transduction mechanisms of C. graminicola that occur as a reaction to different plant-secreted defense molecules. This study shows that C. graminicola oval conidia can sense non host peroxidases via a conserved mechanism using the NADPH oxidase (Nox) complex 2. Moreover, the CgNox2 deletion strain has a penetration defect consistent with other ascomycetes. However, I showed that host-secreted diterpenoids are sensed Nox2 independently. Nevertheless, sensing and signal transduction of both, peroxidases and diterpenoids, requires the cell-wall integrity (CWI) pathway scaffold protein Cgso and the GPCR CgSte3. (III) The third project investigated pH as a factor in the germling fusion of ascomycetes. I collected the secretome of both C. graminicola conidia types and found that they differ in pH, with oval conidia secretome being more acidic. Subsequently, I identified a gradient starting from pH 7.5 as a chemoattractive signal for oval conidia which is perceived by the GPCR CgSte3. Furthermore, signal transduction requires cell wall integrity (CWI) pathway scaffold CgSo and the pheromone response pathway (PRP) mitogen-activated protein kinase (MAPK) CgMk1. Characterization of the CgMk1 deletion strain showed that it is fusion deficient as described for other ascomycetes. Further, this study shows that C. graminicola interacts with the ascomycete species Neurospora crassa and Botrytis cinerea. For all three species, the intraspecies interactions take place preferentially in acidic conditions.
Keywords: Colletotrichum graminicola; Maize; GPCR; MAPK pathway; NADPH oxidase; chemotropism; maize root exudate; Microbiology; Plant-microbe interaction
