Maize bronze 1:dSpm insertion mutations that are not fully suppressed by an active Spm

Area of Science:

• Molecular Biology
• Genetics
• Plant Science

Background:

• The Suppressor-mutator (Spm) family comprises autonomous Spm and nonautonomous defective Spm (dSpm) elements in maize.
• dSpm insertions in genes can allow expression without Spm activity, which is then suppressed by Spm.
• Spm's subterminal repetitive regions (SRRs) possess 12-bp repeat motifs, hypothesized to mediate suppression by blocking transcriptional readthrough.

Purpose of the Study:

• To investigate the role of Spm's subterminal repetitive regions (SRRs) in the suppression of gene expression.
• To determine if the number of SRR repeat motifs is sufficient for complete Spm-mediated suppression.

Main Methods:

• Analysis of the bz-m13 allele, containing a dSpm insertion in the maize Bronze-1 (Bz) gene.
• Characterization of four intra-dSpm deletion derivatives of bz-m13.
• Assessment of Bz gene expression in the presence and absence of Spm activity for each derivative.

Main Results:

• The bz-m13 allele shows significant Bz expression without Spm activity, fully suppressed by Spm.
• dSpm deletion derivatives retained at least 12 SRR repeat motifs but exhibited only partial suppression by Spm.
• The number of SRR repeat motifs alone does not guarantee complete Spm-mediated suppression.

Conclusions:

• The presence of SRR repeat motifs is necessary but not sufficient for complete Spm-mediated gene suppression.
• Other factors, potentially secondary structure or element size, likely contribute to the efficiency of Spm suppression.