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Related Experiment Videos

Molecular organization and germinal instability of R-stippled maize

W B Eggleston1, M Alleman, J L Kermicle

  • 1Laboratory of Genetics, University of Wisconsin, Madison 53706, USA.

Genetics
|September 1, 1995
PubMed
Summary

The spotted seed allele (R-st) involves strong seed color (Sc) and an inhibitor element (I-R). Loss of I-R results in fully colored seeds, indicating its role in seed color regulation.

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Area of Science:

  • Genetics
  • Molecular Biology
  • Plant Science

Background:

  • The R-stippled (R-st) allele controls seed spotting and is composed of strong seed color (Sc), inhibitor-of-R (I-R), and near-colorless seed (Nc) genetic components.
  • The inhibitor-of-R (I-R) element is mobile and irregularly represses Sc expression, with its loss leading to fully colored seeds.

Purpose of the Study:

  • To investigate the genetic structure and regulatory mechanisms of the R-stippled (R-st) allele.
  • To elucidate the role of the inhibitor-of-R (I-R) element in seed color phenotype and its relationship with r genes.

Main Methods:

  • Southern blot analysis was used to examine the r-hybridizing segments within the R-st allele and its deletion products.
  • Comparative analysis with published r gene structures was performed to infer gene content and organization.

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Main Results:

  • R-st contains four r-hybridizing segments, with deletion products showing three, two, or one segment, each presumed to contain at least one r gene.
  • The proximal Sc gene confers strong seed color, while three distal r genes contribute to the near-colorless phenotype.
  • A 3.3-kb insert, identified as I-R, in Sc correlates with the seed spotting phenotype. The level of the near-colorless phenotype is inversely related to the number of r genes, suggesting copy number-dependent silencing.
  • Phenotypic changes in R-st primarily arise from unequal exchange between r genes, with a strong polarity towards the 3' portions of these genes.

Conclusions:

  • The R-stippled allele's phenotype is determined by the interplay of multiple r genes and the mobile I-R element.
  • Unequal exchange events, particularly in the 3' regions of r genes, are the primary drivers of R-st allele variation and phenotypic changes.
  • A multiple copy silencing mechanism likely regulates the expression of distal r genes involved in the near-colorless phenotype.