Plant mutations: slaying beautiful hypotheses by surprising evidence
Résumé
The Weismann theory (1) states that hereditary traits are transmitted exclusively from the germline. The theory is valid in most animals (2) where germline cells are set aside early in development (1). In plants, germline segregation is generally assumed to occur late in development (3-5), which leads to several predictions on the fate of somatic mutations occurring in plant tissues: mutations have generally low frequency in plant tissues (6); mutations at high frequency have a higher chance of intergenerational transmission; branching topology of the tree dictates mutation distribution (7); and, exposure to UV radiation increases mutagenesis (8). We produced a unique plant dataset of 60 high-coverage whole-genome sequences of two tropical tree species and identified 18,274 de novo somatic mutations, almost all at low frequency in tissues. We demonstrate that: 1) low-frequency mutations are transmitted to the next generation; 2) mutation phylogenies deviate from the branching topology of the tree; and 3) mutation rates and mutation spectra are not demonstrably affected by differences in UV exposure. Altogether, our results suggest far more complex links between plant growth, ageing, UV exposure, and mutation rates than commonly thought.