Abstract
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 microalga Graesiella emersonii–Amoeboaphelidium protococcarum interaction. 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, similar to plant defense response, 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. 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. These results suggest that G. emersonii has a conserved defense system against pathogen and that endoparasite A. protococcarum possesses a robust pathogenicity to infect the host. Our study characterizes the first transcriptomic profile of microalgae–endoparasite interaction, providing a new promising basis for complete understanding of the algal host defense strategies and parasite pathogenicity.
Highlights
Microscopic observation of the infection progress revealed that A. protococcarum was an endoparasite that can occupy the microalgal host cell and replace the host cytoplasm (Figure 1a)
Given the above-mentioned enriched pathways in the microalga G. emersonii during infection, we focused on the pathways of ubiquitin-mediated proteolysis and endocytosis
The SignalP 4.0 (Petersen et al 2011), TMHMM v. 2.0, TargetP-2.0 Server, and kohgpi-1.5 programs (GPI-SOM database) were used. This is the first report on microalgae–endoparasite interaction at the transcriptional level
Summary
Oleaginous microalgae have been suggested as a promising feedstock for biodiesel production [1]. Oleaginous microalgae cultivation, combined with wastewater treatment and CO2 mitigation, has been suggested as an environmentally sustainable process with the production of high value-added bioproducts [2,3]. The mass cultivation of microalgae is susceptible to microbial contamination (especially parasitic fungi), which can lead to algal culture crashes [4]. Algal parasites are a key driving factor in phytoplankton seasonal successions [5]. In the mass cultivation of microalgae, these parasites can cause microalgal population crashes and trigger further damage to their valuable products [6].
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