Assessment Of Somaclonal Variation In Maize Intra-specific Hybrids And Their Parental Inbrid Lines

Somaclonal variation refers to genetic and/or epigenetic changes that arise through the culture of plant cells, tissues and organs, which was suggested to hold great promise in crop genetic improvement.In this study, three elite maize inbred lines were selected and were crossed with each other to produce two sets of reciprocal hybrids (Mo17×78599 and Mo17×C8605-2), and an efficient tissue culture protocol was developed for embryogenic callus culture and plant regeneration from immature embryos of these plant lines. Genetic and epigenetic instabilities in the callus and regenerated plants of all the seven genotypes were assessed by AFLP and MSAP marks.The main results obtained in this study were summerized as following:1. Genotype had an important effect on the induction frequency of callus derived from immature embryos in maize. Hybrids always showed a higher induction frequency han inbred lines, though no discernibale differnce was observed in the reciprocal crosses.2. Tissure culture induced both genetic and epigenetic (based on different levels and patterns of DNA methylation) variations in all the maize hybrids and inbred lines. Again, no difference was detected between the cross directions.3. The 7 genotypes showed more or less similar frequencies of genetic variations. The regenerants showed lower levels of variation compared to callus.4. For most genotypes, the levels of both hemi-methylation at external Cs and full-methylation at internal Cs at CCGG sites showed demethylation in calli, and followed by hyper methlation in the regenerants. In general, the frequencies of demethylation (0.9%-9.2%)were hiher than hypermethylation (0.6%-3.6%.5. Correlation analysis of the genetic and epigenetic instabilities by Mentel test indicated that there existed a significant correlation between AFLP and MSAP both in Mo17×78599 (r=0.8145,1,000 permutations,p<0.01)and Mo17×C8605-2 (r=0.8640, 1,000 permutations, p<0.01), which suggested the existance of some intrinsinc interrelatedness between genetic variation and epigenetic variations.6. BLAST results of isolated variable sequences showed that the alterations occurred in diverse sequences including cellular genes, transposons ,ESTs and sequences of unknown function. A majority of DNA methylation alterations occured randomly, but a few did not.