It has recently been proposed as the official primary barcoding marker for fungi (Deliberation of 37 mycologists from 12 countries at the Smithsonian’s Conservation and Research Centre, Front Royal, Virginia, May 2007). More than 100 000 fungal ITS sequences generated by conventional Sanger sequencing are deposited in the International Nucleotide Sequence Databases and/or
other databases , providing a large reference material for identification of fungal taxa. However, these data are to some extent hampered by misidentifications or technical errors such as mixing of DNA templates or sequencing errors . Furthermore, a large amount of partial ITS sequences generated by next-generation sequencing has Selleck MI-503 recently been deposited in public sequence databases. The ITS region includes the ITS1 and ITS2 regions, separated by the 5.8S gene, and is situated between the 18S (SSU) and 28S (LSU) genes in the nrDNA repeat unit (Figure 1). The large number of ITS copies per cell (up to 250; ) makes the region an appealing target for sequencing environmental substrates where the quantity of DNA
present is low. The entire ITS region has commonly been targeted with traditional Sanger sequencing approaches and typically ranges between 450 and 700 bp. Either the ITS1 or the ITS2 region have been targeted in recent high-throughput sequencing check details studies [14–17], because the entire ITS region is still too long for 454 sequencing or other high-throughput sequencing methods. Using high-throughput sequencing, thousands of sequences can be analysed from a single environmental sample, enabling in-depth analysis of the fungal diversity. Various primers Farnesyltransferase are used for amplifying the entire or parts of the ITS region (Figure 1). The most commonly used primers were published
early in the 1990′s (e.g. [18, 19] when only a small fraction of the molecular variation in the nrDNA repeat across the fungal kingdom was known. Several other ITS primers have been published more recently  but have not been used extensively compared to the earlier published primers. However, little is actually known about the potential biases that commonly used ITS primers introduce during PCR amplification. Especially during high-throughput sequencing, where quantification (or semi-quantification) of species abundances is also possible to a certain degree (although hampered by factors like copy-number variation), primer mismatches might potentially introduce large biases in the results because some taxonomic groups are favoured during PCR. Our main focus in this study is on the two dominating taxonomic groups of fungi in the Dikarya, Ascomycota and Basidiomycota.