Preliminary Study On The Mutation Pattern Of Somatic Cells In Woodland Strawberry(Fragaria Vesca)

During the development of animals,the germline is segregated early in development thereby preventing mutations in somatic cells from being transmitted to progeny.Given the non-transmissibility of somatic mutations,the selection pressure on somatic cells may be lower than that on germ cells during long-term evolution.Therefore,the researchers assumed that mitosis has a higher mutation rate,but this hypothesis is difficult to be directly tested in animals.Since the flowering of plants generally occurs in the later period of plant growth,it is generally believed that the differentiation of plant germ cells and somatic cellhave s is relatively late.However,with the deepening of research,more and more experiments speculated that plants may have the same early separation and shelving of germ cells as animals,but this is controversial due to lack of clear evidence.Therefore,this study intends to use woodland strawberry as the research object,through the systematic tracking of the mutation rate and mutation inheritance relationship of different tissues,to explore whether the plant has the differentiation of tissue cells and the separation of germ cells.First,woodland strawberry has the characteristics of small genome(240 Mb),and it is relatively economical to detect and track mutations;Secondly,unlike the common cultivated strawberry(octaploid),woodland strawberry is diploid and easy to carry out genetic analysis;Thirdly,strawberries can be asexually propagated by the number of runner producing a large number of seedlings.On the one hand,it is conducive to the long-term tracking of somatic cells and germ cells;on the other hand,clear tissue differentiation is easy to detect mutations and trace lineages,providing a basis for the separation of germ cells and the testing of tissue mutation heterogeneity.Genomic sequencing of 49 samples(45 leaves,4 runner)showed that the mutation rate of ranner was higher than that of leaves of branched seedlings(runner=4.75/sample,leaves = 1.93/sample),indicating that the mutation rate of different tissues might have higher heterogeneity.Analysis of the lineages and histological locations of the mutations showed that runner mutations could be transmitted across the branch seedlings but could not be detected in the branch seedlings.This indicates that the stem cells of runner elongation and axillary meristem have differentiation and isolation,that is,there may be isolated stem cell layer in runner of strawberry.Only some of the mutations in the stem cell layer can be transmitted to the propagating plant and even to the offspring,thus acting as "germ cells",while the somatic mutations in the remaining stem cell layers will not be transmitted and inherited.Hence,the mutations detected in the runner mainly represent non-hereditary mutations,and the mutations in the leaves of the expanded plants are more likely to represent hereditary mutations,thus conforming to the hypothesis of the adaptive evolution of the previously proposed mutation rate.Such a tissue specificity of somatic mutation may be widespread in various plants,so this study will provide more clues for other similar studies.It could also provide a practical model for the existence of a true"germline"in plants and for the isolation of stem cells.