Comparative transcriptomics provides a powerful tool to identify the genes related to developmental differences in closely related organisms. In this study, we examined transcriptional similarities and differences during the stages of spore germination/initial infection stages of Fusarium graminearum and Metarhizium anisopliae, two related fungal species with distinct lifestyles. F. graminearum is a plant pathogen and the causal agent of Fusarium head blight on cereal crops, whereas M. anisopliae is an insect pathogen and root endophyte that forms beneficial associations with barley. Four conidial germination stages were selected for transcriptome analysis on the host, and on a common growth medium: fresh conidia, polar growth, doubling of the long axis, and first hyphal branching. A substantial difference was shown in the transcriptome of spore germination stages between F. graminearum and M. anisopliae when colonizing barley. F. graminearum expressed a higher number of genes encoding CAZymes and specialized metabolites during host colonization, whereas M. anisopliae did not. Both fungal species showed upregulated putative effector genes, particularly proteins with the LysM domain during early colonization events with more effector putative effectors upregulated in F. graminearum. Moreover, candidate genes associated with indole-3-acetic acid synthesis were upregulated during the appressorial stage in M. anisopliae, but not F. graminearum. We have also characterized the formation of biofilms in F. graminearum, which provides a basis for understanding the functionality of biofilms in the pathogen disease cycle. Collectively, these studies provide valuable insights into the network of genes necessary for spore germination, pathogenesis/symbiosis and significantly broadens our transcriptome data resources on fungal-plant interactions.

Acknowledgments

Funding was provided by U.S. Department of Agriculture, under agreement no. 59-0206-0-152 to F.T. This is a cooperative project with the U.S. Wheat and Barley Scab Initiative. This material is based upon work supported by the US Department of Agriculture National Institute of Food and Agriculture under Award No. 2020-67013-31185 to FT. We also acknowledge the support of Michigan State University AgBioResearch.