GPCR genes as activators of surface colonization pathways in a model marine diatom

Surface colonization allows diatoms, a dominant group of phytoplankton in oceans, to adapt to harsh marine environments while mediating biofoulings to human-made underwater facilities. The regulatory pathways underlying diatom surface colonization, which involves morphotype switching in some species, remain mostly unknown. Here, we describe the identifications of 61 signaling genes, including G-protein-coupled receptors (GPCRs) and protein kinases, that are differentially regulated during surface colonization in the model diatom species, Phaeodactylum tricornutum. We show that the transformation of P. tricornutum with constructs expressing individual GPCR genes induces cells to adopt the surface colonization morphology. P. tricornutum cells transformed to express GPCR1A display 30% more resistance to UV light exposure than their non-biofouling wild type counterparts, consistent with increased silicification of cell walls associated with the oval-biofouling morphotype. Our results provide a mechanistic definition of morphological shifts during surface colonization and identify candidate target proteins for the screening of eco-friendly, anti-biofouling molecules.

Methods
Total RNA extraction was performed using the MagMAX-96 Total RNA Isolation kit AM1830 with all necessary reagents (Thermo Fisher Scientific Inc.) according to the manufacturer’s instruction. The complementary DNA (cDNA) libraries were prepared using the TruSeq RNA Library Preparation kit v2 (Illumina) according to the manufacturer’s instruction as previously described (Fu et al., 2017). After quality inspection, the library was quantified by quantitative PCR for cluster generation on the Bot system and then sequenced using paired-end sequencing of 2 × 100–base pair read length on an Illumina HiSeq 2500 system.