Multi-Omics Profiling of the Scaphoideus titanus Yeast-Like Symbiont Guides the Bioinformatic Discovery of Related Fungal Symbioses in Insects.

Symbiotic partnerships have opened new ecological niches and contributed to the remarkable diversification of insects. The leafhopper Scaphoideus titanus, a phloem-feeding insect known to be the primary vector of Flavescence dorée phytoplasma, harbours two primary endosymbionts: the bacterium 'Candidatus Karelsulcia muelleri' and a yeast-like symbiont (YLS). While most studies on insect-associated microorganisms have focused on obligate bacterial symbionts, fungal endosymbionts, although documented for almost a century, are only now gaining renewed attention for their evolutionary and ecological significance. In this study, we integrated genomic and proteomic data with phylogenetic analyses to elucidate the functional and evolutionary features of the YLS associated with S. titanus. Using a data-independent proteomic approach supported by a newly sequenced symbiont genome, we defined the proteins expressed by the YLS that may contribute to host physiology. Comparative analyses across the five currently available YLS genomes enabled a proteome-wide phylogenetic reconstruction within the genus Ophiocordyceps, refining the evolutionary placement of these symbioses. Finally, large-scale mining of NCBI transcriptomic Sequence Read Archive datasets using a novel computational workflow, combined with an extensive literature survey, identified several new candidate insect hosts and provided a comprehensive inventory of species harbouring these fungal partners.