Copy number analyses of DNA repair genes reveal the role of poly(ADP-ribose) polymerase (PARP) in tree longevity.

Long-lived organisms are exposed to the risk of accumulating mutations due to DNA damage. Previous studies in animals have revealed the positive relationship between the copy number of DNA repair genes and longevity. However, the role of DNA repair in the lifespan of plants remains poorly understood. Using the recent accumulation of the complete genome sequences of diverse plant species, we performed systematic comparative analyses of the copy number variations of DNA repair genes in 61 plant species with different lifespans. Among 121 DNA repair gene families, PARP gene family was identified as a unique gene that exhibits significant expansion in trees compared to annual and perennial herbs. Among three paralogs of plant PARPs, PARP 1 showed a close association with growth rate. PARPs catalyze poly(ADP-ribosyl)ation and play pivotal roles in DNA repair and antipathogen defense. Our study suggests the conserved role of PARPs in longevity between plants and animals.

Low mutation rates promote the evolution of advantageous traits by preventing interference from deleterious mutations.

We studied how mutation rates promote the evolution of advantageous traits in an asexual population. First, to examine the effects of mutation rates on the evolution of an advantageous trait (high competitive ability), we carried out simulation analyses with competition between individuals for survival. Second, to examine the mechanism underlying the promotion of advantageous trait evolution, we calculated the probabilities that new favorable effects of mutations on the phenotype were acquired and that existing favorable effects were maintained. In the simulation analyses, advantageous traits evolved in the population with a low mutation rate; however, when the mutation rate was extremely low, advantageous traits evolved slowly because few beneficial mutations occurred. Then, the numerical calculations showed that the probability of acquiring new favorable effects of mutations on the phenotype and the probability of maintaining existing favorable effects are high if the mutation rate is low. The former occurs because, if the mutation rate is high, multiple mutations may occur in a genome, and even if beneficial mutations occur, their favorable effects may be masked by simultaneously occurring deleterious mutations. However, if the mutation rate is low, it is likely that only one beneficial mutation occurs, and its favorable effect on the phenotype is direct. In conclusion, low mutation rates are advantageous because they promote favorable phenotypic effects of mutations without interference from deleterious mutations; these low rates not only prevent the occurrence of deleterious mutations but also help maintain existing beneficial mutations and promote the evolution of advantageous traits.

Ovule and seed production patterns in relation to flower size variations in actinomorphic and zygomorphic flower species.

Zygomorphic flower species tend to show lower flower size variation than actinomorphic flower species. Have these differences also brought an association in ovule and seed production that has arisen due to natural selection in these species? Flowers were collected from 29 actinomorphic and 20 zygomorphic flower species, and fruits were collected from 21 actinomorphic and 14 zygomorphic flower species in Miyagi and Aomori prefectures, in Japan. The coefficient of variations (CVs) of flower sizes, mean ovule sizes of flowers, ovule numbers of flowers and mean seed sizes of fruits were calculated. The CV of flower sizes was marginally different between the floral symmetry types; tending to be lower in the zygomorphic flower species than in the actinomorphic flower species. The CVs of mean ovule sizes and ovule numbers of flowers increased with increase in the CV of flower sizes in the actinomorphic flower species but not in the zygomorphic flower species. Mean ovule number of flowers tends to increase with increase in mean flower size in the actinomorphic flower species but not in the zygomorphic flower species. The degrees in variations in ovule size and number of flowers were influenced by the interaction of floral symmetry type and flower size variation, suggesting that floral symmetry also has brought an evolutionary association in ovule production by flowers.

Evolution towards minimum ovule size? Ovule size variations and the relative sizes of ovules to seeds.

BACKGROUND AND AIMS: Is there selection minimizing the costs of ovule production? Such selection should lead to a smaller ovule size in relation to seed size and, at the same time, smaller variation in ovule size within plants, the latter because the minimum structures and resources for functioning of ovules should be the same among ovules. Additionally, within species, ovule size should not depend on the plant's resource status. METHODS: To confirm these predictions, we examined ovule and seed production for a variety of species. KEY RESULTS: Among the 27 species studied, we found a significant negative dependence of the species mean of the coefficient of variation for plant ovule size on the ratio of the mean species seed size/mean species ovule size. Thus, the smaller the ovule size as compared with seed size, the smaller the degree of variation in ovule size. Among the 49 species studied, only two species showed significant positive dependence of mean ovule size on plant size. Although larger plants should have greater resources for ovule production, selection has not enhanced the production of large ovules in most species. CONCLUSIONS: These results suggest that there is selection minimizing the costs of ovule production.