| Although mutation is a fundamental process in evolution and disease, little is known about the factors that affect the mutation rate, especially for plants. Five separate studies were conducted, each aimed towards the assessment of factors that affect the mutation rate in seed plants. Firstly, from an examination of molecular evolutionary rates of selectively neutral DNA (which equals the mutation rate) of phylogenetically independent pairs of closely related plant species, it was shown that, contrary to widely accepted opinion, generation time does not generally affect molecular evolutionary rates in plants. Secondly, an analysis of molecular evolutionary rates of selectively neutral maternally and paternally inherited organellar DNA of gymnosperms, lead to the discovery that the sperm contains more selectively neutral mutations than an egg. Thirdly, from the comparison of the fitness effects of UV on maternal and pollen parents, it was demonstrated that more deleterious mutations in the nuclear genome are transmitted by a sperm than by an egg in Arabidopsis thaliana. Fourthly, an assessment of the parallels between the p53-related pathway, the most well-characterized process for DNA repair in humans and mice, and the process of germination of aged seeds (which contain DNA damage) indicated that plants may eliminate DNA damage by a p53-related pathway. Fifthly, it is described why, in many cases, the mutation rate does not almost entirely depend on replication errors arising during the synthesis (S) stage of the cell cycle, as contended by many studies, but also depends on factors other than S-stage replication errors. Overall, the results suggest that although generation time does not influence the mutation rate in plants, gender does affect both the neutral mutation rate and the transmission of deleterious mutations. The implications of these results to understanding the cause of most mutations are discussed. |
