Transcriptome Metabolic Characterization of <em>Tuber borchii</em> SP1, a New Spanish Strain for<em> In Vitro</em> Studies of the Bianchetto Truffle

Abstract

Truffles are ascomycete hypogeous fungi belonging to the Tuberaceae family of the Pezizales order that grow in ectomycorrhizal symbiosis with tree roots and are known for their peculiar aromas and flavors. Axenic culture of truffle mycelium is problematic because it is not possible in many cases, and the growth rate is meager when it is possible. This limitation prompts searching and characterizing new strains that can be handled in laboratory conditions for basic and applied studies. In this work, a new strain of Tuber borchii (strain SP1) has been isolated and cultured, and its transcriptome has been analyzed under different in vitro culture conditions. The results show that the best T. borchii SP1 growth was obtained using maltose-enriched cultures made with soft-agar and in static submerged cultures made at 22ºC. The transcriptome analysis of this strain cultured in different media indicated that most of the gene transcription effort is due to a limited number of genes (20% of genes account for 80% of the transcription), that the transcription profile of the central metabolism genes was similar in the different conditions analyzed with a transcription signal detected for around 80% of the annotated genes. The gene expression profile suggests that T. borchii uses a fermentative rather than respiratory metabolism, even in aerobic conditions. Finally, there is a reduced expression of genes belonging to secondary metabolite clusters, whereas there is a significative transcription of those involved in producing volatile aromatic compounds.