Related Experiment Videos
Characterization of primary lesions caused by the plastome mutator of Oenothera
T L Chang1, L L Stoike, D Zarka
1Department of Botany and Plant Pathology, Michigan State University, East Lansing, MI 48824-1312, USA.
Abstract:
Oenothera plants homozygous for a recessive allele at the plastome mutator (pm) locus show non-Mendelian mutation frequencies that are 1000-fold higher than spontaneous levels. Characterization of RFLP sites in a collection of mutants indicates that insertion-deletion hot spots in the pm lines are defined by tandem direct repeats, implicating replication slippage or misalignment during recombination. Several sites known to contain very short direct repeats were examined, and all were found to have been targeted in one or more plants of the mutant collection. To determine if replication slippage was occurring, two oligo-A stretches in non-coding DNA were examined, and 3 of 12 plants were found to have an additional adenine in a 13-base track. To search for other mutations that would not be visible as restriction fragment length polymorphisms, PCR-amplification products of the psbB gene were digested with a restriction endonuclease, denatured, and examined for single-strand conformational polymorphisms. Among 21 mutants, one 4-bp insertion and one point mutation were identified in psbB. The discovery that the plastome mutator can cause base substitutions as well as repeat-mediated insertions and deletions points to a likely defect in a component of the cpDNA replication machinery.
Insights
The plastome mutator (pm) in Oenothera plants causes 1000-fold higher mutation rates. This mutator targets tandem repeats, suggesting replication errors, and causes insertions, deletions, and base substitutions in cpDNA.
Area of Science:
- Plant genetics
- Molecular biology
- Evolutionary biology
Background:
- The plastome mutator (pm) locus in Oenothera plants significantly elevates mutation frequencies in chloroplast DNA (cpDNA).
- Spontaneous mutation rates are dramatically increased (1000-fold) in pm lines, indicating a major genetic factor influencing cpDNA stability.
Purpose of the Study:
- To investigate the molecular mechanisms underlying the high mutation rates observed in Oenothera plastome mutator lines.
- To characterize the types and locations of mutations induced by the plastome mutator.
- To identify potential defects in the cpDNA replication machinery.
Main Methods:
- Restriction fragment length polymorphism (RFLP) analysis of cpDNA.
- Polymerase chain reaction (PCR) amplification and analysis of specific genes (e.g., psbB).
- Single-strand conformational polymorphism (SSCP) analysis to detect sequence variations.
Main Results:
- Insertion-deletion hotspots in pm lines are associated with tandem direct repeats, suggesting replication slippage or misalignment.
- Analysis of non-coding DNA revealed adenine insertions in repeat regions, supporting replication slippage.
- SSCP analysis of the psbB gene identified a 4-bp insertion and a point mutation, indicating base substitutions also occur.
Conclusions:
- The plastome mutator induces both repeat-mediated insertions/deletions and base substitutions in cpDNA.
- These findings implicate a defect in a component of the chloroplast DNA replication machinery.
- The study provides insights into the molecular basis of cpDNA mutation and evolution.