Genetic and epigenetic changes induced by maize tissue culture

The efficiency of crop improvement can presumably be enhanced via a somatic cell genetic system. Effective procedures for transformation also focus on the use of cultured cells. Although genetic variation is a critical element of plant breeding, many of the applications of cell and tissue culture depend on genetic stability. Tissue culture induced variation appears to be a common features of most tissue culture systems, the frequency of which depends on several factors, including the genomic structure of the species. An understanding of the mechanisms leading to this variation is important relative to attempts to manipulate the frequency. Previous studies with maize have documented the occurrence of single gene mutations, chromosomal aberrations, quantitative trait variation, transposable element activation and changes in DNA methylatin. The data on methylation reported on here show that hypomethylation occurs 3.5 times more frequently than hypermethylation among regenerated lines, massive genomic methylation does not occur, changes in methylation are often detected in normally transcribing genes, and base changes are relatively rare. In addition, 24% of the 756 regenerant family-probe combinations tested revealed homozygous DNA methylation changes in the original regenerated plant. Information on the role of methylation with regard to DNA binding proteins is discussed relative to these results. (author). 60 refs, 2 tabs