The Norway spruce genome sequence gives insights into conifer genome evolution: Transcriptome Assembly

Conifers have dominated forests for more than 200 million years and are of huge ecological and economical importance. We present the draft assembly of the 20 Gbp genome of Norway spruce (Picea abies), the first genome sequence available for any gymnosperm. The number of well-supported genes (28,354) was similar to the >100 times smaller genome of Arabidopsis thaliana and there was no evidence of a recent whole-genome duplication. Instead, the large genome size has resulted from the slow and steady accumulation of a diverse set of LTR TEs, probably due to the lack of an efficient elimination mechanism. Comparative sequencing of Pinus sylvestris, Abies sibirica, Juniperus communis, Taxus baccata and Gnetum gnemon revealed that the TE diversity is shared among extant conifers. Expression of 24nt sRNAs, previously implicated in TE silencing, was tissue-specific and much lower than in other plants. We further identified numerous long (>10,000 bp) introns, gene like fragments, uncharacterized long non- coding RNAs and short RNAs. This opens up new genomic avenues for conifer forestry and breeding.