Picea abies (L.) H.Karst. (Pinaceae)


Norway spruce

The Norway spruce is a cone-bearing tree (conifer) that grows in the cooler parts of Europe. Conifers are a group of plants called the gymnosperms that produce naked seeds. That is, their seeds are not fully surrounded by a layer of maternal tissue that forms a fruit or a rind.

The oldest known fossil gymnosperms are approximately 370 million years old and these plants continued to dominate the Earth's flora for the next 300 million years. Despite their ancient history, modern conifers are remarkably similar. Compare pines (Pinus) and monkey puzzles (Araucaria). Both are trees, produce needle-shaped leaves and cones containing seeds.

This lack of morphological diversity in such an ancient group of plants has long puzzled scientists. Recently an explanation for the relative paucity of conifer diversity has come from an analysis of the Picea abies genome. The sum total of the genetic material - DNA - of an organism is its 'genome'. It includes all the genes that are required for life including those that control shape and form. It has long been known that conifer genomes are among the largest of any organism - the Picea abies genome contains six times more DNA than the human genome.

Analysis of the Picea abies genome revealed that contrary to expectations, the conifer genome is really quite simple. All this DNA encodes approximately 28,000 genes - almost the same number as the tiny thale cress (Arabidopsis thaliana). What makes the Norway spruce genome so large is the vast number of virus-related DNA sequences that have inserted themselves between each of the genes.

The authors, who include John MacKay, the new Wood Professor of Forest Science, conclude that the large numbers of virus-related sequences have increased the amount of DNA in conifers to such an extent that 'genome paralysis' through 'genome obesity' has occurred! They hypothesize that this paralysis limited the amount of morphological diversity that evolved in conifers.

In contrast, the genomes of flowering plants have not experienced 'genome paralysis'. They underwent extensive genetic rearrangements that generated the enormous genetic variation underpinning the evolution of the huge diversity of morphologies.

Sequencing the genome of Picea abies has provided insight into one of the great mysteries of botany. As DNA sequencing becomes cheaper and the genomes of more plants are decoded, we will get explanations for many of the botanical conundrums that have confounded humanity for much more than 400 years.

Further reading
Nystedt B et al 2013. The Norway spruce genome sequence and conifer genome evolution. Nature 497, 579-584.

Sederoff R 2013. A spruce sequence. Nature 497, 569-570.

Liam Dolan