title: Variation in genomic methylation in natural populations of chinese white poplar.
abstract: BACKGROUND
  It is thought that methylcytosine can be inherited through meiosis and mitosis, and that epigenetic variation may be under genetic control or correlation may be caused by neutral drift. However, DNA methylation also varies with tissue, developmental stage, and environmental factors. Eliminating these factors, we analyzed the levels and patterns, diversity and structure of genomic methylcytosine in the xylem of nine natural populations of Chinese white poplar.
  
  
  RESULTS
  On average, the relative total methylation and non-methylation levels were approximately 26.567% and 42.708% (P<0.001), respectively. Also, the relative CNG methylation level was higher than the relative CG methylation level. The relative methylation/non-methylation levels were significantly different among the nine natural populations. Epigenetic diversity ranged from 0.811 (Gansu) to 1.211 (Shaanxi), and the coefficients of epigenetic differentiation (GST  = 0.159) were assessed by Shannon's diversity index. Co-inertia analysis indicated that methylation-sensitive polymorphism (MSP) and genomic methylation pattern (CG-CNG) profiles gave similar distributions. Using a between-group eigen analysis, we found that the Hebei and Shanxi populations were independent of each other, but the Henan population intersected with the other populations, to some degree.
  
  
  CONCLUSIONS
  Genome methylation in Populus tomentosa presented tissue-specific characteristics and the relative 5'-CCGG methylation level was higher in xylem than in leaves. Meanwhile, the genome methylation in the xylem shows great epigenetic variation and could be fixed and inherited though mitosis. Compared to genetic structure, data suggest that epigenetic and genetic variation do not completely match.
authors.affiliation: National Engineering Laboratory for Tree Breeding, College of Biological Sciences and Technology, Beijing Forestry University, Beijing, PR China.
authors.forename: Kaifeng
authors.initials: K
authors.lastname: Ma
authors.forename: Yuepeng
authors.initials: Y
authors.lastname: Song
authors.forename: Xiaohui
authors.initials: X
authors.lastname: Yang
authors.forename: Zhiyi
authors.initials: Z
authors.lastname: Zhang
authors.forename: Deqiang
authors.initials: D
authors.lastname: Zhang
mesh_terms: D001483:Base Sequence; D002681:China; D019175:DNA Methylation / Q000235:genetics*; D044127:Epigenesis, Genetic; D014644:Genetic Variation; D018745:Genome, Plant / Q000235:genetics*; D016133:Polymerase Chain Reaction; D011110:Polymorphism, Genetic; D032107:Populus / Q000235:genetics*; D025341:Principal Component Analysis