Germ Line and Somatic Mutator Activity: Are they Functionally Related?
Results of experiments to test for a relationship, if any, between somatic Mutator (Mu) activity (somatic mutability) and germline Mu activity are described. Somatic Mu activity was measured by the intensity of the mutable pattern in unstable al-Mum aleurone mutants. Germinal activity was determined by the frequency with which a Mu plant transmitted new mutants to its outcross progeny plants. None of the experiments demonstrated tight linkage between these two Mu-regulated phenomena. Not all plants with intense somatic mutability patterns exhibited germline activity. Nor did all plants that had little or no somatic mutability lack germinal activity. In one inbred lineage, which had retained an intense somatic mutability pattern for four generations, there was a sudden shift to low somatic mutability in the progeny of the fifth generation. Some representatives of this lineage, taken from different generations but all with intense mutability, had germinal activity, but others did not. The same was true for the low-intensity lines observed in the progeny of the fifth generation. The lines with a low-intensity somatic mutability pattern had Mu elements that were modified at their HpaII sites. This modification was found in “low” somatic mutability lines with and “low” somatic mutability lines without germinal Mu activity.
At present, there is insufficient evidence to establish how germline activity and somatic mutability in Mutator stocks are regulated and if they are regulated via a common mechanism. There is evidence that DNA modification is involved in both phenomena, but more information on the state of modification of the element inserted at the mutant aleurone locus in different situations with respect to levels of somatic mutability and germinal activity is needed before the role of modification in these two aspects of the Mutator system can be fully understood. What role, if any, putative regulators of somatic activity have in germinal activity is yet to be determined.
KeywordsSomatic Mutability Mutable Seed Stable Derivative Mutability Score Medium Mutability
Unable to display preview. Download preview PDF.
- 3.Bennetzen, J.L. (1984) Transposable element Mul is found in multiple copies only in Robertson’s Mutator maize lines. J. Molec. Appl. Genet. 2:519–524.Google Scholar
- 4.Bennetzen, J.L. (1985) The regulation of Mutator function and Mu1 transposition. In Plant Genetics, U.C.L.A. Symposium on Molecular and Cellular Biology, Vol. 35, M. Freeling, ed. Alan R. Liss, New York, pp. 317–331.Google Scholar
- 5.Bennetzen, J.L. (1987) Covalent DNA modification and the regulation of Mutator element transposition in maize. Molec. Gen. Genet. 208:454–451.Google Scholar
- 10.Fedoroff, N.V. (1983) Controlling elements in maize. In Mobile Genetic Elements, J. Shapiro, ed. Academic Press, New York, pp. 1–63.Google Scholar
- 12.Maniatis, T., E.F. Fritsch, and J. Sambrook (1982) Molecular Cloning: A Laboratory Manual. Cold Spring Harbor Laboratory, Cold Spring Harbor, New York.Google Scholar
- 13.Rivin, C.J., E.A. Zimmer, and V. Walbot (1982) Isolation of DNA and RNA recombinants from maize. In Maize for Biological Research, W.F. Sheridan, ed. Plant Molecular Biology Association, Charlottesville, Virginia, pp. 161–164.Google Scholar
- 17.Robertson, D.S. (1986) Loss of Mu mutator activity when active Mu systems are transferred to inbred lines. Maize Genet. Coop. Newsl. 60:10.Google Scholar
- 18.Robertson, D.S. (1987) Mendelian ratios in crosses of mutable Mutator-induced al mutants. Maize Genet. Coop. Newsl. 61:11–13.Google Scholar
- 19.Robertson, D.S., P.S. Stinard, J.G. Wheeler, and D.W. Morris (1985) Genetic and molecular studies on germinal and somatic mutability in Mutator-induced aleurone mutants of maize. In Plant Genetics, U.C.L.A. Symposium on Molecular and Cellular Biology, Vol. 35, M. Freeling, ed. Alan R. Liss, New York, pp. 317–331.Google Scholar
- 20.Roth, B.A. (1987) Robertson’s Mutator system in maize: Studies on the regulation of activity and the prevalence of Mu1-homologous DNA sequences in diverse lines of maize. Ph.D. Dissertation, Iowa State University, Ames.Google Scholar
- 24.Taylor, L.P., V.L. Chandler, and V. Walbot (1986) Insertion of 1.4 kb Mu elements into the bronzel gene of Zea mays L. Maydica 31:31–45.Google Scholar
- 26.Walbot, V., and C. Warren (1987) Regulation of Mu element copy number in maize lines with an active or inactive Mutator transposable element system. Molec. Gen. Genet. (in press).Google Scholar