A mutant lectin gene is rescued from an insertion element that blocks its expression

Area of Science:

• Molecular biology
• Plant genetics
• Gene regulation

Background:

• Soybean lectin (Le1) is a highly regulated seed protein.
• A mutant allele (le1) shows no detectable transcription and a lectinless phenotype.
• The le1 allele contains a Tgm1 insertion element within its coding region.

Purpose of the Study:

• To investigate if the Tgm1 insertion element or a secondary mutation represses le1 gene transcription.
• To determine the role of the Tgm1 element in the lectinless phenotype.

Main Methods:

• Constructed a chimeric le1/Le1 gene combining 5' le1 and 3' wild-type Le1 gene segments.
• Introduced the chimeric gene into transformed tobacco seeds.
• Analyzed lectin mRNA and protein production in transformed seeds.

Main Results:

• Transformed tobacco seeds with the le1/Le1 gene produced detectable lectin mRNA and protein.
• Transformed seeds with the original le1 gene produced no detectable lectin mRNA.
• The le1 gene's control region was shown to be transcriptionally competent.

Conclusions:

• The Tgm1 insertion element is responsible for repressing le1 gene transcription.
• The Tgm1 element acts at a distance to inhibit transcription from an upstream promoter.
• This study elucidates the mechanism of transcriptional inhibition by insertion elements in soybean lectin genes.