Organization of paramutagenicity in R-stippled maize.
In heterozygotes, R-stippled (R-st) reduces the pigmenting potential of sensitive r alleles heritably (paramutation). R-st is comprised of four r genes arranged in direct orientation. Unequal crossing over within R-st generates deletion products retaining from one to three r genes. Paramutagenic strength decreased in parallel with copy number, both among internal and distal deletions. Single-gene R-st derivatives were nonparamutagenic. This was so whether or not the single gene retained the transposable element (I-R) responsible for seed spotting. Adding back r genes by intragenic recombination increased paramutagenicity in proportion to total gene number. Each member of a set of overlapping deletions retained moderately strong activity, showing that no single r gene or intragenic region is required for paramutagenicity. Proximal and distal loss R-st derivatives, each retaining two r genes, were less paramutagenic in trans than the corresponding four copy cis combination, indicating R-st's paramutagenic determinants function as a cis-interdependent unit in bringing about modification of a sensitive allele.
Laboratory of Genetics, University of Wisconsin, Madison 53706, USA.
J L
JL
Kermicle
W B
WB
Eggleston
M
M
Alleman
D003434:Crossing Over, Genetic; D017353:Gene Deletion; D017343:Genes, Plant; D005816:Genetic Complementation Test; D016296:Mutagenesis; D009154:Mutation; D010858:Pigmentation / Q000235:genetics*; D018515:Plant Leaves; D003313:Zea mays / Q000235:genetics*