Understanding the genetic diversity and differentiation of the genetic resources of a species is important for the effective use and protection of forest tree resources. Ex situ development is a common method for the protection of genetic diversity and an essential resource for users who require ready access to a species’ germplasm. In this study, we collected seeds of black locust (Robinia pseudoacacia L.) from 19 provenances, covering most of its natural distribution; we randomly selected 367 tender leaves with well-grown and different maternal strains from this group for further analysis. Forty-eight simple sequence repeat (SSR) primers were successfully selected from 91 pairs of SSR primers using native-deformation polyacrylamide gel electrophoresis. In addition, we identified identical genotypes among all individuals and evaluated the quality of the markers. From this, 35 loci were confirmed for analyses of genetic diversity and differentiation of the black locust provenances, which contained 28 expressed sequence tag-derived simple sequence repeats (EST-SSRs) and 7 genomic DNA-derived simple sequence repeats (G-SSRs). We observed high genetic diversity among the native black locust provenances, from which Wright’s fixation index and molecular variance suggested that a majority of the genetic differentiation variation could be attributed to within-provenance differences. The genetic distance and identity results indicated that geographic distance was not a dominating factor influencing the distribution of black locust. This is the first study to evaluate provenance genetic variation in native black locust samples using two types of SSR markers, which provides a comprehensive theoretical basis for ex situ conservation and utilization of genetic resources, with an emphasis on breeding applications.
Robinia pseudoacacia is an important afforestation tree introduced to China in 1878. In the present study, we examined the genetic diversity among 687 strains representing four improved varieties and two secondary provenances, comprising 641 clones and 46 seedlings. Ninety-one simple sequence repeats (SSRs) were selected through segregation analysis and polymorphism characterization, and all sampled individuals were genotyped using well-characterized SSR markers. After excluding loci with non-neutral equilibrium, missing locus data and null alleles, we used 36 primer pairs to assess the genetic diversity of these germplasm resources, revealing vast genetic differentiation among the samples, with an average of 8.352 alleles per locus and a mean Shannon′s index of 1.302. At the population level, the partitioning of variability was assessed using analysis of molecular variance, which revealed 93% and 7% variation within and among collection sites, respectively. Four clusters were detected using structure analysis, indicating a degree of genetic differentiation among the six populations. Insights into the genetic diversity and structure of R. pseudoacacia provide a theoretical basis for the conservation, breeding and sustainable development in China.
An endonuclease was purified from the basidiocarps of the fungus Coprinus cinereus during late premeiotic S-phase, karyogamy, and pachytene stages of meiosis. This endonuclease causes single-strand nicks on supercoiled PM2 DNA. Its activity is dependent on cofactors such as Mg2+ and Ca2+, and is enhanced by hexaminecobalt chloride and dimethylsulfoxide. Treatments with increasing cofactor concentration elicit increasing enzyme activity in vitro and increasing genetic recombination in vivo. The percent recombination that can be induced by cofactor treatment during late premeiotic S-phase, karyogamy and pachytene is correlated with the amount of endonuclease that can be extracted from the respective stages. These results suggest that Mg2+ and Ca2+ induce genetic recombination by increasing the endonuclease activity that creates nicked and gapped DNA substrates for ensuing recombination events. We believe that the meiotic endonuclease of Coprinus is involved in the early phase of genetic recombination. Cold temperature treatment is known to retard repair activity at pachytene and causes a threefold increase in recombination. Double treatments involving Mg2+ and Ca2+ at karyogamy followed by cold temperature at pachytene result in an additive (more than fourfold) increase in recombination frequency. The peak concentration of the nicking endonuclease is found at late premeiotic S and early karyogamy, whereas the peak activity of the repairing DNA polymerase b is found at late pachytene. The staging of these two enzymes is in good accord with the genetic data.Key words: Coprinus, endonuclease, meiosis, genetic recombination, Z-DNA.
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