Transcriptome metabolic characterization of Tuber borchii SP1, a new Spanish strain for in vitro studies of the Bianchetto truffle

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. Gene expression profiling from RNA-seq data in truffle mycelium, Tuber borchii.

块菌（truffle）是隶属于盘菌目（Pezizales）块菌科（Tuberaceae）的子囊菌门地下生真菌，可与树木根系形成外生菌根共生关系，以其独特的香气与风味闻名。块菌菌丝体的无菌纯培养存在诸多局限：多数情况下无法实现，即便培养成功，其生长速率也极为缓慢。这一局限推动研究者探寻并鉴定可在实验室条件下稳定培养的新型菌株，以开展基础与应用研究。本研究分离培养出一株新的博奇块菌（Tuber borchii）SP1菌株，并针对其在不同体外培养条件下的转录组进行了分析。研究结果显示，博奇块菌SP1的最优生长条件为：采用添加麦芽糖的软琼脂培养基，以及22℃下的静态液体浸没培养。对该菌株在不同培养基中培养后的转录组分析表明，基因转录的主要贡献来自少量基因——仅20%的基因贡献了80%的转录总量；在所有分析条件下，中心代谢基因的转录谱均较为相似，约80%的注释基因可检测到转录信号。基因表达谱显示，即便在有氧条件下，博奇块菌也采用发酵而非呼吸代谢途径。最后，属于次级代谢产物合成基因簇的基因表达量较低，而参与挥发性香气物质合成的基因则呈现显著的转录水平。本数据集为基于RNA测序获得的博奇块菌菌丝体基因表达谱数据。