Collaborative Research: Processes and Consequences of Somatic Mutation Accumulation in Plants

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This project will address the long-standing question of whether mutations during stem growth (somatic mutations) in plants undergo natural selection within the adult plant, are passed to offspring, and affect the fitness of those offspring. Mutation is the ultimate source of variation for evolution and adaptation, but unless a mutation is inherited in the next generation, it will not affect evolution. In animals, only mutations that occur during the development of the sperm and egg are heritable. However, plants differ from animals, because they can accumulate additional somatic mutations. Despite this extra source of genetic variation in plants, overall mutation rates are similar between plants and animals. One potential explanation for this paradox is that somatic mutations are filtered by natural selection as plants grow. This process is predicted to remove harmful mutations and to retain beneficial ones, which could affect plant vigor in subsequent generations. Using the yellow monkeyflower (Mimulus guttatus), this project will provide the first comprehensive tests of this filtering process. The results from this project will also have important applications for the fields of plant breeding, agriculture, and conservation biology. Additionally, this project will involve high school, undergraduate, and graduate students in hands-on research experiences.Despite the potential for somatic mutations to generate novel genetic variation in plant populations, their role in plant evolution remains almost entirely unexplored. Preliminary findings demonstrate that individual stems can possess unique complements of somatic variants, and that somatic mutations can have substantial effects on seedling vigor. Moreover, models predict the maintenance of moderate numbers and constant turnover of somatic mutations as stems grow. This project will test the assumptions and predictions of these models by: i) examining the distribution of shared somatic mutations in reproductive and vegetative tissues, ii) estimating rates of mutation turnover under high and low salinity stress, iii) identifying the genomic effects associated with the appearance of beneficial mutations, and iv) evaluating the consequences of somatic mutations on seedling vigor. Genomic sequencing will allow somatic mutations to be tracked through time along individual stems to estimate rates of turnover and to reveal the presence of beneficial mutations. Finally, this project will test the potential for somatic mutations to contribute to adaptive evolution by contrasting the responses to stress in selection lines propagated by different mating strategies. The outcomes of this work will reveal the genomic and phenotypic consequences of somatic mutations in plants and will improve our understanding of plant evolution.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.