An Apomixis-Gene's view on Dandelions

Abstract

In asexual organisms, the clone constitutes a level above the individual. Most dandelions (Taraxacum officinale s.l.) reproduce asexually through apomixis, asexual reproduction through seeds. A clone can be seen as a superorganism that is born, that growths, degenerates and eventually dies. Apomixis in dandelions is controlled by a few dominant genes, the so called apomixis-genes. This implies that there should be three hierarchical levels in a field of dandelions: 1. the individual plant, 2. the clone and 3. the apomixis gene. Using co-dominant genetic markers that are linked to a dominant apomixis gene, we provide evidence that this hierarchical structure indeed exists in apomictic dandelion populations. The apomixis gene view implies that whereas individual clones may go extinct due to deleterious mutation accumulation or the lack of adaptive potential, apomixis genes can prevail much longer periods of evolutionary time in a succession of clones. We provide evidence that an apomixis-gene in Taraxacum is not transmitted to diploid offspring, which could explain the absence of apomixis in diploid dandelions. Haploid non-transmission may be caused by a mutation load that is linked to the apomixis genes as a consequence of the deep asexual reproduction history of these genes residing in many clones in the past.