Related Experiment Video
Updated: Aug 19, 2026
Using Ustilago maydis as a Trojan Horse for In Situ Delivery of Maize Proteins
Published on: February 8, 2019
The structure and paramutagenicity of the R-marbled haplotype of Zea mays
T Panavas1, J Weir, E L Walker
1Biology Department, University of Massachusetts, Amherst, Massachusetts 01003, USA.
Abstract:
Paramutation is the meiotically heritable silencing of a gene that can occur in particular heterozygous combinations. The R-marbled (R-mb) haplotype is paramutagenic: it causes paramutable r1 haplotypes like R-r to become heritably silenced. R-mb was found to comprise three distinct r1 genes arranged as direct repeats. The most distal gene of R-mb, Scm, contains a novel transposable element, Shooter (Sho). Excision of the Sho element early in aleurone development results in the characteristic "marbled" aleurone pigmentation pattern conferred by R-mb. The effect of gene copy number on the paramutagenic strength of R-mb was tested. Paramutagenic strength of R-mb is directly correlated with r1 gene copy number. Paramutagenic strength of R-mb is directly correlated with r1 gene copy number. Paramutagenic strength of R-mb was not affected by removal, through crossing over, of the Sho transposon. Finally, R-mb does not appear to contain the transposable element, Doppia, which is associated with paramutability of R-r, and has been suggested to play a role in paramutagenicity of another paramutagenic haplotype, R-stippled.
Insights
Paramutation involves gene silencing in specific gene combinations. The R-marbled (R-mb) haplotype
Area of Science:
- Genetics
- Epigenetics
- Plant Biology
Background:
- Paramutation is a heritable gene silencing phenomenon observed in specific heterozygous combinations.
- The R-marbled (R-mb) haplotype is known to induce paramutation in other r1 haplotypes, such as R-r.
- The R-mb haplotype consists of three direct repeat r1 genes, with the most distal gene, Scm, containing the novel transposable element Shooter (Sho).
Purpose of the Study:
- To investigate the relationship between gene copy number and the paramutagenic strength of the R-mb haplotype.
- To determine the role of the Shooter (Sho) transposable element in the paramutagenicity of R-mb.
- To explore the presence of the Doppia transposable element in R-mb and its potential role in paramutation.
Main Methods:
- Experimental crosses were performed to generate varying gene copy numbers of the R-mb haplotype.
- Genetic analysis was conducted to assess the paramutagenic strength of R-mb under different conditions.
- Molecular techniques were employed to examine the presence and excision of transposable elements, including Sho and Doppia.
Main Results:
- Paramutagenic strength of R-mb was found to be directly correlated with the number of r1 gene copies.
- Removal of the Sho transposon through crossing over did not affect the paramutagenic strength of R-mb.
- The R-mb haplotype does not appear to contain the Doppia transposable element.
Conclusions:
- Gene copy number is a critical factor influencing the paramutagenic strength of the R-mb haplotype.
- The Sho transposable element is not essential for the paramutagenic activity of R-mb.
- The absence of Doppia in R-mb suggests it may not be universally required for paramutation across different haplotypes.
Related Concept Videos
01:18Dihybrid Crosses
02:27Trihybrid Crosses
Some of Mendel’s crosses examined three pairs of contrasting characteristics. Such a cross is called a trihybrid cross. A trihybrid cross is a combination of three individual monohybrid crosses. For example, plant height (tall vs. short), seed shape (round vs. wrinkled), and seed color (yellow vs. green).
The F1 generation plants of a trihybrid cross are heterozygous for all three traits and produce eight gametes. Upon self-fertilization, these gametes have an equal chance to...