THE PLANT CELL, Vol 4, Issue 9 1141-1146, Copyright © 1992 by American Society of Plant Biologists
A Mutant Lectin Gene Is Rescued from an Insertion Element That Blocks Its Expression
J. K. Okamuro and R. B. Goldberg
Department of Biology, University of California, Los Angeles, California 90024-1606
The soybean lectin gene Le1 encodes a prevalent seed protein and is highly
regulated during the life cycle. The mutant lectin gene allele Ie1 is not
transcribed detectably, contains a 3.5-kb Tgm1 insertion element within its
coding region 0.6 kb 3[prime] to the transcription start site, and leads to
a lectinless phenotype. To determine whether the Tgm1 element or a
secondary mutation was responsible for repressing Ie1 gene transcription,
we eliminated the insertion element by constructing a chimeric lectin gene
(Ie1/Le1) that contained the 5[prime] half of the Ie1 gene and its promoter
region and the 3[prime] half of the wild-type Le1 gene. Transformed tobacco
seed containing the Ie1/Le1 gene produced both lectin mRNA and protein,
demonstrating that the mutant lectin gene control region is
transcriptionally competent. By contrast, transformed seed containing the
Ie1 gene produced no detectable lectin mRNA. We conclude that the absence
of detectable transcription from the Ie1 gene is due to transcriptional
inhibition by the Tgm1 insertion element and that this element acts at a
distance to block transcription from an upstream promoter region.
