Limited tissue culture-induced mutations and linked epigenetic modifications in F hybrids of sorghum pure lines are accompanied by increased transcription of DNA methyltransferases and 5-methylcytosine glycosylases.

In plant tissue culture, developmental disturbance and mutagenic factors are involved in channeling an individual totipotent cell to an intact plant. Comparing a pair of sorghum reciprocal F(1) hybrids with their parental pure lines revealed a dramatic difference in the occurrence of both genetic and DNA methylation alterations in the respective regenerated plants. In contrast to those of the pure lines, regenerated plants of hybrids exhibit significantly enhanced genetic and epigenetic stability. The genetic changes detected by amplified fragment length polymorphism and the DNA methylation alterations detected by methylation-sensitive amplified polymorphism are intimately correlated with each other, suggesting a common mechanism underlying both kinds of instabilities. Markedly altered transcription of genes encoding four putative sorghum DNA methyltransferases and two 5-methylcytosine glycosylases with nucleotide sequences orthologous to Arabidopsis counterparts was induced by tissue culture. The steady-state transcript levels of these genes were negatively correlated with genetic and methylation alterations. A salient observation is that tissue culture-induced transcription of genes encoding DNA methyltransferases and 5-methylcytosine glycosylases in calli and/or regenerated plants of the hybrids was remarkably coordinated, but is largely uncoordinated and stochastically altered in calli and/or regenerated plants of the pure lines. We suggest that the uncoordinated regulation of expression of DNA methyltransferases and 5-methylcytosine glycosylases is a major cause of the high incidence of genetic and DNA methylation alterations in cultures of pure lines, but coordinated up-regulated expression of these enzymes in cultures of the F(1) hybrids fortified their genetic and epigenetic stability.