Enhanced selenium tolerance and selenium nanoparticles biosynthesis in Chlamydomonas reinhardtii expressing Auxenochlorella pyrenoidosa selenocysteine lyase

Low levels of selenium can promote plant growth, but higher concentrations are toxic. Aquatic environments usually contain more selenium than terrestrial habitats, leading aquatic algae to develop efficient detoxification mechanisms to counteract selenium toxicity. The selenocysteine lyase gene plays a key role in reducing selenium toxicity and in biosynthesizing selenium nanoparticles. In this study, we found that Auxenochlorella pyrenoidosa exhibited the most efficient capability for synthesizing selenium nanoparticles among different algal species. The selenocysteine lyase gene ApScl was further identified from the Auxenochlorella pyrenoidosa genome, and the predicted protein structure of ApScl was consistent with the previously characterized class II cysteine desulfurases. Selenium tolerance experiments in Arabidopsis thaliana and Chlamydomonas reinhardtii overexpressing ApScl gene revealed that the ApScl enhanced selenium tolerance in both species and improved selenium nanoparticles biosynthesis efficiency in Chlamydomonas reinhardtii . Transcriptome analysis revealed that the most of differentially expressed genes in the oxidation-reduction process pathway were significantly downregulated in the ApScl overexpressed Chlamydomonas reinhardtii , indicating that the ApScl gene overexpression weakened the antioxidant defense capacity of the algal cells. These findings not only reveal the function of ApScl in microalgal selenium detoxification but also provide new insights into selenocysteine lyase–mediated selenium nanoparticles biosynthesis. • Pyrenoidosa exhibits the most efficient capability for synthesizing SeNPs. • ApScl enhances selenium tolerance and promotes SeNPs biosynthesis in C. reinhardtii . • ApScl gene plays an important role in regulating cellular redox processes.