UC Davis

Redwood (Sequoia sempervirens (D. Don) Endl.) is a long-lived, clonal, hexaploid tree species. Their longevity brings into focus questions about their genomic stability and integrity. Without a defined germline, mutations that accumulate in the branches of a plant may end up in sexual offspring, leading to possible decline of the population through propagation of deleterious mutations. To investigate how somatic mutations accumulate, we sequenced fourteen branches from a single 1400-year-old, 107-meter-tall redwood tree and germinated seedlings from cones from the two tops of this tree. Within the tree, the two tops had different fecundity (cone size, seed size, and seedling germination) attributable to a chromosomal deletion in one of them. Genomic and anatomical evidence suggests redwood trees have two coexisting cell lineages (tunica-corpus; L1, L2) within their usually stratified shoot apical meristems whose phenotypic expression is determined largely by normal branch ontogeny and parent branch selection. These separate cell lineages directly affect how mutations can accumulate in a redwood tree, which mutated lineages proliferate, and the extent to which any lineage contributes to sexual offspring. Redwoods usually show separation of cell lineages in their shoot apical meristems and different branch ontogeny which are shared with many other seed plants. Decoupling of stratified shoot apical meristem cell lineages through branching events leading to different fecundity between branches may well occur in other species, affecting per-generation mutation rate and genetic diversity in plant populations.