Genome Report: A reference genome sequence for the exceptionally long-lived Great Basin bristlecone pine, <i>Pinus longaeva</i>

Great Basin bristlecone pine (Pinus longaeva), one of two species of bristlecone pine, the other being Rocky Mountain bristlecone pine (P. aristata), is endemic to the high Great Basin mountains in eastern California, Nevada, and Utah. It is the upper treeline forest tree in this region, found mostly between 2900 m and 3600 m. The primary goal of this project was to generate a reference genome sequence for P. longaeva that, among its many possible applications, will serve as an important genetic resource to better understand the genetic mechanisms underlying is extreme longevity and its adaptation to the extreme environmental conditions where it is found. A combination of short-read and long-read sequences were generated from haploid megagametophyte and diploid needle tissues, respectively. A customized genome assembly approach was used to construct a highly contiguous 23.8-gigabase genome with a scaffold N50 size of 1.2 gigabases. The chloroplast and mitochondrial genomes were assembled separately into circular chromosomes with lengths of 120 kilobases and 8.68 megabases, respectively. While the number of disease resistance genes known as nucleotide-binding leucine-rich repeat receptors (NLRs) and larger-than-average telomere lengths relative to other conifers have been suggested as genetic mechanisms for controlling longevity, we did not find strong evidence for their involvement. Clearly further study is needed.