Paramutation in Plants

Abstract

Paramutation describes a directed, meiotically heritable alteration of gene regulation influenced by allelic interactions.

Keywords: gene silencing; epigenetics; transgenes; transcription; chromatin

Figure 1.

Paramutation behaviour. Anther phenotypes and corresponding diploid genotypes are represented for two sets of genetic crosses that together illustrate the nonmendelian inheritance pattern typifying paramutation. Pl‐Rhoades (Pl‐Rh) and Pl′ alleles control anthocyanin pigment production in the anthers (see text).

Figure 2.

Allelic interaction models. Two general models of allelic interactions mediating trans‐silencing. Solid horizontal arrows represent gene sequences and grey dots represent chromosome materials unfavourable to gene transcription. Bidirectional arrow indicates a diffusible substance. (a) Allelic interaction involving transfer of chromosome materials via physical pairing of homologous sequences. (b) Allelic interaction involving transfer of a diffusible substance.

Figure 3.

Paramutation phenotypes. Visible pigment phenotypes conferred by paramutable and paramutagenic alleles or haplotypes are displayed. (a) B‐I versus B′ leaf sheath phenotypes. (b) Pl‐Rh versus Pl′ anther phenotypes. (c) R‐r:std, R‐r:std′, R‐st and R‐mb kernel phenotypes.

Figure 4.

Paramutable versus paramutagenic allele and haplotype structures. Schematics (not to scale) represent genome organizations of the various alleles and haplotypes referred to in the text. Solid black arrows denote transcribed regions. Open boxes represent repetitive regions. Small horizontal triangles represent individual repeats; in the pl1 and p1 alleles these represent 3′ regions of the respective transcribed regions. Vertical triangles denote the presence of transposable elements. Hash marks indicate large regions of intervening sequences. Several individual r1 units are labeled; P is only expressed in the plant, S1 and S2 regions are expressed in the kernel, Self coloured (Sc) and Self coloured marbled (Scm) are highly expressed in kernels but are interrupted by the presence of two unrelated transposable elements. Somatic excisions of these elements from Sc and Scm during kernel development restore gene function and give rise to the pigment patterns displayed in Figure . Remaining unlabelled r1 regions are very weakly expressed in kernels.

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References

Brink RA (1956) A genetic change associated with the R locus in maize which is directed and potentially reversible. Genetics 41: 872–890.

Brink RA (1973) Paramutation. Annual Review of Genetics 7: 129–152.

Chandler VL, Eggleston WB and Dorweiler JE (2000) Paramutation in maize. Plant Molecular Biology 43: 121–145.

Coe EH Jr (1959) A regular and continuing conversion‐type phenomenon at the B locus in maize. Proceedings of the National Academy of Sciences of the USA 45: 828–832.

Hagemann R (1969) Somatic conversion (paramutation) at the sulfurea locus of Lycopersicon esculentum Mill III. Studies with trisomics. Canadian Journal of Genetics and Cytology 11: 346–358.

Hollick JB, Patterson GI, Coe EH Jr, Cone KC and Chandler VL (1995) Allelic interactions heritably alter the activity of a metastable maize pl allele. Genetics 141: 709–719.

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Stam M, Belele C, Dorweiler JE and Chandler VL (2002) Differential chromatin structure within a tandem array 100 kb upstream of the maize b1 locus is associated with paramutation. Genes and Development 16: 1906–918.

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Further Reading

Brink RA, Styles ED and Axtell JD (1968) Paramutation: directed genetic change. Science 159: 161–170.

Coe EH Jr (1966) The properties, origin and mechanism of conversion‐type inheritance at the b locus in maize. Genetics 53: 1035–1063.

Chandler VL, Eggleston WB and Dorweiler JE (2000) Paramutation in maize. Plant Molecular Biology 43: 121–145.

Hollick JB, Dorweiler JE and Chandler VL (1997) Paramutation and related allelic interactions. Trends in Genetics 13: 302–308.

Lisch D, Carey CC, Dorweiler JE and Chandler VL (2002) A mutation that prevents paramutation in maize also reverses Mutator transposon methylation and silencing. Proceedings of the National Academy of Sciences of the USA 99(9): 6130–6135.

Russo VEA, Martienssen RA and Riggs AD (eds) (1996) Epigenetic Mechanisms of Gene Regulation. Cold Spring Harbor, NY: Cold Spring Harbor Laboratory Press.

Stam M, Belele C and Ramakrishna W et al. (2002) The regulatory regions required for B′ paramutation and expression are located far upstream of the maize b1 transcribed sequences. Genetics 162: 917–930.

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How to Cite close
Hollick, Jay B(May 2005) Paramutation in Plants. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0001199]