Re-evaluating the driving force behind mutations

Abstract

Experiments on tropical trees suggest that new mutations in plants are driven by age rather than number of cell divisions during growth.

Keywords: evolution; evolutionary biology; genetics; genomics; heritable mutations; plants; tropical trees.

Figure 1.. Testing what drives mutations in animals and plants.

There are two hypotheses for how mutations appear and are putatively passed down to future offspring: through errors during DNA replication (cell division hypothesis), or unrepaired damage accumulating with age (age-related hypothesis). To test what drives germline mutations in animals (left panel), previous studies compared the age of the maternal parent at conception to the number of new mutations in the offspring of mammals. This revealed a positive correlation between the two variables (bottom graph, green tick). As oocytes stop dividing in childhood once they are fully formed, this suggests that heritable mutations are caused by age-related damage, not replication errors. Despite being typically harder to observe in males, heritable mutations transmitted from the paternal parent have also recently been shown to be consistent with the age-related hypothesis (Hahn et al., 2023). To test the two hypotheses in plants (right panel), Satake et al. calculated the number of somatic mutations per metre of growth in two evolutionary related tropical trees: a slow-growing (blue) and a fast-growing (green) species that were of similar heights but different ages. The two trees acquired somatic mutations at different rates (right graph), and the gap between these slopes corresponded to the age difference between them. This suggests that the age-related hypothesis also applies to plants (bottom panel, green tick), suggesting that there are parallels in how mutations arise in plants and animals, at least between mammals and trees.