Multi‐omics reveal the pathways involved in induced defensive colony formation of Tetradesmus obliquus in response to Daphnia grazing cues

Abstract

AbstractInducible defenses occur in various taxa of prey organisms. Many phytoplankton species, including the freshwater Chlorophyta Tetradesmus spp., can form defensive morphs under the zooplankton‐released grazing cues. However, definite statements on the actual mechanisms of inducible defense in phytoplankton are quite deficient. In the present study, the defensive mechanism of Tetradesmus obliquus (formerly known as Scenedesmus obliquus) induced by Daphnia infochemicals was analyzed through multifaceted analyses integrating physiological and biochemical monitoring, transcriptomics, and metabolomics. Results showed that the upregulated genes encoding G protein‐coupled receptor and phospholipase C were involved in the perception and transduction of grazing cues, and the transcripts related to extracellular polysaccharides formation and transductions were upregulated. The results provided molecular evidence for the role of extracellular polysaccharides in colony formation. Increased lipid content revealed through metabolomics suggested higher investment in lipid biosynthesis within colonial cells, whereas the downregulation of ribosome‐related pathways indicated less allocation of energy and resources to protein biosynthesis. The significant increase in indole‐3‐acetic acid content indicated that growth was activated under grazing cues. This study provided essential information on the inducible defensive mechanism of Tetradesmus and direct evidence for the intracellular reallocation of resources and energy owing to the defensive colony formation, which had considerable implications for enriching the theory of inducible defenses at the molecular level.