Format: ORAL

Andrew R. Leitch1, Marie Henniges1, 2, Joseph Morton1, 2, 3, Lubna Faizullah1, 2, Xiaotong (Elaine) Wang1, 2, Jaume Pelicer2, Maite Guignard1, 2, Erika Hersch-Green3, Ilia J. Leitch2.

1 Queen Mary University of London, London, UK 2 Royal Botanic Gardens, Kew, Surrey, UK 3 Michigan Technological University, Houghton, Michigan, USA

The amount of DNA in each cell of an organism, called the genome size, varies enormously between species. Indeed, amongst flowering plants there is a known ~2,500 fold range in genome size (from 60,000 -160,000,000 bp per 1C genome). However, most plant species have smaller genomes than would be expected given the incidence of polyploidy and (retro)transpostion in their ancestries, suggestive of evolutionary selection against large genome sizes. This talk first explores ecological selection acting on genome size, focussing in particular on nutrient limitation. We show from grassland nutrient experiments in UK, Germany, Inner Mongolia and from the Nutrient Network that species with large genomes are favoured in the presence of nitrogen and phosphate fertilizers, suggestive of ecological selection against large genomes when they are limiting (as in most soils of the world). But it is unknown if such ecological selection translates to evolutionary selection against large genomes, because available data suggests that there are only small rates of DNA loss per generation (470 Mb/million years, 500 bp/generation). This poses a problem as to how evolutionary selection might act, given that the size of even the smallest plant genome is three orders of magnitude larger than these DNA losses. We propose that a solution to this problem might be that genome downsizing is an emergent property of polyploidy, which after time has ecological advantages to plants growing in nutrient poor habitats.