December 22, 2022  |  Plant + animal biology

The HiFi difference Christmas edition – Big genomes

PacBio holiday logoThis year, the scientific community has achieved many “firsts” – across genomes, transcriptomes, epigenomes, metagenomes, and more – with long and accurate HiFi sequencing. Another, seasonally timely, “first” was just reported by the Darwin Tree of Life Consortium, announcing the construction of the European mistletoe genome, the largest genome of any species from Britain and Ireland. At around 90 billion base pairs (90 Gbp), which is an astounding thirty times larger than the human genome, it is also the largest reference genome — assembled to a level representing all the chromosomes — thus far. Compared to the 23 human chromosome pairs, mistletoe only has ten, which in conjunction with its enormous genome size means that individual mistletoe chromosomes are many times larger than the entire human genome!

mistletoe genome discovery

As is standard practice with reference genomes today, the genome of this giant is also based on HiFi sequencing, carried out by the researchers at the Wellcome Sanger Institute, using their Sequel IIe systems. The high accuracy and uniformity of the HiFi data allowed for efficient algorithms to construct the genome assembly, thereby scaling to genome sizes much larger than the human genome. It is remarkable to think that even just a few years ago anyone who would have suggested assembling a genome this large would have been considered to having had a bit too much eggnog!

The mistletoe is much more than a simple gesture of holiday cheer. In fact, the mistletoe has both dramatic and positive effects on the biodiversity surrounding it. Some species of mistletoe have a crucial role in the way an ecosystem functions. But its benefits also go beyond keeping the balance of its environment too. There’s growing evidence suggesting some mistletoe species can help reduce the side effects of chemotherapy, helping patients tolerate cancer treatment.

In addition to the exciting biology of the mistletoe that awaits from mining this new reference genome, it is a testament that with HiFi sequencing, no genome is too big, or too complex, to prevent a reference-quality architectural blueprint of a species. This shift in the landscape of genomics is foundational to the many ongoing biodiversity and conservation genomics initiatives (highlighted in a previous post), and will now scale even more with the higher-throughput Revio system next year!

With heartfelt wishes for the holidays, we would like to thank all our customers for connecting with us, and we already look forward to continuing our partnership in the new year – with many more genomes (big and small!), and the resulting incredible science and amazing discoveries!

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