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BIOlogie et GEstion des Risques en agriculture - Champignons Pathogènes des Plantes

Impact of biotic and abiotic factors on the expression of fungal effector-encoding genes in axenic growth conditions

Meyer's publication in Fungal Genetics and Biology
The repression of expression of effector genes in axenic conditions seems to be a general trait in filamentous phytopathogens. In this paper, Meyer and colleagues at BIOGER identify for the first time biotic and abiotic stresses that are able to derepress the expression of effector genes in axenic cultures of the phytopathogenic fungus Leptosphaeria maculans.

In phytopathogenic fungi, the expression of hundreds of small secreted protein (SSP)-encoding genes is induced upon primary infection of plants while no or a low level of expression is observed during vegetative growth. In some species such as Leptosphaeria maculans, this coordinated in-planta upregulation of SSP-encoding genes expression relies on an epigenetic control but the signals triggering gene expression in-planta are unknown. In the present study, biotic and abiotic factors that may relieve suppression of SSP-encoding gene expression during axenic growth of L. maculans were investigated. Some abiotic factors (temperature, pH) could have a limited effect on SSP gene expression. In contrast, two types of cellular stresses induced by antibiotics (cycloheximide, phleomycin) activated strongly the transcription of SSP genes. A transcriptomic analysis to cycloheximide exposure revealed that biological processes such as ribosome biosynthesis and rRNA processing were induced whereas important metabolic pathways such as glycogen and nitrogen metabolism, glycolysis and tricarboxylic acid cycle activity were downregulated. A quantitatively different expression of SSP-encoding genes compared to plant infection was also detected. Interestingly, the same physico-chemical parameters as those identified here for L. maculans effectors were identified to regulate positively or negatively the expression of bacterial effectors. This suggests that apoplastic phytopathogens may react to similar physiological parameters for regulation of their effector genes.


Meyer M., Bourras S., Gervais J., Labadie K., Cruaud C., Balesdent M.-H. & Rouxel T. (2017) Impact of biotic and abiotic factors on the expression of fungal effector-encoding genes in axenic growth conditions. Fungal Genetics and Biology, 99, 1-12. doi :10.1016/j.fgb.2016.12.008