Physiological and Dual Transcriptional Analysis of Microalga Graesiella Emersonii–Amoeboaphelidium Protococcarum Pathosystem Uncovers Conserved Defense Response and Robust Pathogenicity

Abstract Background: The oleaginous microalga Graesiella emersonii, a potential industrial strain for lipid production, is frequently infected by the endoparasite Amoeboaphelidium protococcarum. It is essential to investigate the microalgae–endoparasite interaction to prevent and control microalgal diseases. However, the underlying mechanisms of microalgal host-pathogen interactions remain largely unknown. In this study, we applied physiological and simultaneous dual transcriptomic analysis to characterize the G. emersonii–A. protococcarum interaction for the first time. Results: Three infection stages were determined according to infection rate and physiological features. Dual RNA-seq results showed that the genes expression of G. emersonii and A. protococcarum were strongly dynamically regulated during the infection. For microalgal hosts, the expression of defense genes involved in the pattern recognition receptors, large heat shock proteins, and reactive oxygen scavenging enzymes (glutathione, ferritin, and catalase) were significantly upregulated during infection. However, some genes encoding resistance proteins (R proteins) with a leucine-rich repeat domain exhibited no significant changes during infection. Furthermore, ubiquitin-mediated proteolysis and endocytosis were strongly affected by A. protococcarum infection. For endoparasite A. protococcarum, genes for carbohydrate-active enzymes, pathogen-host interactions, and putative effectors were significantly upregulated during infection. Furthermore, the genes in cluster II were significantly enriched in pathways associated with the modulation of vacuole transport, including endocytosis, phagosome, ubiquitin-mediated proteolysis, and SNARE interactions in vesicular transport pathways.Conclusions: Our data provide a new promising basis for complete understanding of the algal host defense strategies and parasite pathogenicity. This is beneficial for the screening of resistant microalgal strains and developing control strategies for microalgal diseases.