Plant Cuttings

Giant organisms, giant genomes…

Humans are 98% junk! But a carnivorous plant is far more efficient - containing only 3% junk-DNA.
Image: Wikimedia Commons.
Image: Wikimedia Commons.

A deluge of plant genomes for you this month (what is the collective name for loads of genomes – an embarrassment?). First a brace of gymnosperm genomes: the ginormous 20 gigabases of Norway Spruce (Picea abies) announced by Björn Nystedt et al., and the similarly sized genome of white spruce (P. glauca) published by Inanc Birol et al. At a size 20 times larger than arabidopsis’ sequencing, these huge genomes presents ‘unique challenges’, according to Birol et al. However, now those challenges have been overcome it is hoped that these genomics resources will be useful for improved forest management of, and conservation efforts for, these trees, which, as major representatives of conifers, are of ‘huge ecological and economic importance’ (Nystedt et al.), globally. Hmm, Norwegian wood, isn’t it good? Hands up all those who aren’t singing the lyrics to The Beatles’ song of the same name. From the very big to the more compact now with Enrique Ibarra-Laclette et al. and the much more modest 82-megabase genome of the carnivorous bladderwort Utricularia gibba. One of the main interests in this plant’s genome is its tiny size, but which still ‘accommodates a typical number of genes for a plant, with the main difference from other plant genomes arising from a drastic reduction in non-genic DNA’. Non-genic – or non-coding DNA, which doesn’t code for protein sequences – is often termed ‘junk DNA’. Humans have about 98 % of so-called junk DNA, bladderwort has 3 %, which makes plants much more DNA-efficient than humans: result! Finally, Ray Ming and co-workers have sequenced the genome of the sacred lotus, Nelumbo nucifera. I say ‘finally’ merely to indicate the pause for this quartet of genomes in this news item. But it may be that such reports have had their day if David Smith is correct in his thoughtful opinion article entitled ‘Death of the genome paper’. So, DNA RIP? I doubt it – those sequencers have to pay for themselves somehow! But it is important that behind the morass – however impressive it may appear! – of bases and sequence data we ‘don’t lose the organism in the excitement over its genes’.

[Interestingly, Robert Lanfear et al. have discovered that taller plants have lower rates of molecular evolution, which may explain why gymnosperms have been around for hundreds of millions of years (almost unchanged), whereas arabidopsis has undergone unprecedented amounts of genetic change and mutation in only the last 40 years(!). Well, that, the massive discrepancy in size of their respective genomes, and the intensive artificial-selection pressures foisted on thale cress by over-zealous molecular botanists. And, incidentally ‘tall’ is the Swedish word for … pine! – Ed.]