Molecular organization and germinal instability of R-stippled maize.
The spotted seed allele R-stippled (R-st) is comprised of the following genetic components: strong seed color (Sc), inhibitor-of-R (I-R) and near-colorless seed (Nc). I-R is a mobile element that represses (Sc) expression irregularly. Germinal I-R losses produce progeny with fully colored seed. Southern blot analysis revealed four r-hybridizing segments in R-st and three, two or one in two sets of unequal crossover deletion products. By comparison to published reports of r gene structure, we maintain that each segment contains at least one r gene. The proximal r gene, Sc, confers strong seed color; the three distal r genes together produce near-colorless seed. R-st's seed spotting phenotype is correlated with the presence of a 3.3-kb insert in Sc identified as I-R. The level of the near-colorless phenotype is inversely correlated with the number of r genes present, suggesting involvement of a multiple copy silencing mechanism in their regulation. Phenotypic changes in R-st occurred primarily by unequal exchange between r genes. The locations of exchange positions showed a strong polarity, nearly all occurring in the 3' portions of the identified r genes.
Laboratory of Genetics, University of Wisconsin, Madison 53706, USA.
W B
WB
Eggleston
M
M
Alleman
J L
JL
Kermicle
D000483:Alleles; D003596:Cytosine / Q000378:metabolism; D017343:Genes, Plant; D006720:Homozygote; D008745:Methylation; D010641:Phenotype; D010858:Pigmentation / Q000235:genetics*; D003313:Zea mays / Q000235:genetics*
D003596:Cytosine