The mutant STE 1 was isolated by screening an ethylmethane sulfonate (EMS)-mutagenized population of Arabidopsis thaliana which consisted of 22,000 M2 plants divided into 1100 pools of 20 plants by gas chromatography of sterols extracted from small leaf samples. STE 1 was characterized by the accumulation of three delta 7-sterols concomitantly with the decrease of the three corresponding delta 5-sterols which are the end products of the sterol pathway in wild-type leaves. The structure of these delta 7-sterols was determined after two steps of purification on HPLC, by gas chromatography coupled with mass spectrometry (GC-MS) and proton nuclear magnetic resonance spectrometry (1H-NMR). The accumulation of delta 7-sterols suggested that the mutant is deficient in the activity of the delta 7-sterol-C-5-desaturase. Genetic analysis showed that the accumulation of delta 7-sterols was due to a single recessive nuclear mutation. The mutant line STE 1 was backcrossed four times to the wild-type. The resulting STE 1 plants had wild-type morphology and set seeds normally, suggesting that the delta 7-sterols in STE 1 are good surrogates of physiologically active delta 5-sterols to sustain normal development. STE 1 roots were transformed with the Saccharomyces cerevisiae ERG 3 gene encoding the delta 7-sterol-C-5-desaturase under the control of the CaMV 35S promoter. Seven transgenic STE 1 root-derived calli showed an increase in delta 5-sterols and a concomitant decrease in delta 7-sterols in comparison with STE 1 untransformed root-derived calli. Northern blot analysis using the ERG 3 probe showed a strong expression of ERG 3 in three of the seven transgenic calli. These results suggest that the accumulation of delta 7-sterols in the STE 1 mutant is due to a deficiency of the delta 7-sterol-C-5-desaturation step in the plant sterol biosynthesis pathway.
|Evidence ID||Analyze ID||Interactor||Interactor Systematic Name||Interactor||Interactor Systematic Name||Type||Assay||Annotation||Action||Modification||Phenotype||Source||Reference||Note|
|Evidence ID||Analyze ID||Gene||Gene Systematic Name||Gene Ontology Term||Gene Ontology Term ID||Qualifier||Aspect||Method||Evidence||Source||Assigned On||Annotation Extension||Reference|
|Evidence ID||Analyze ID||Gene||Gene Systematic Name||Phenotype||Experiment Type||Experiment Type Category||Mutant Information||Strain Background||Chemical||Details||Reference|
|Evidence ID||Analyze ID||Regulator||Regulator Systematic Name||Target||Target Systematic Name||Experiment||Assay||Construct||Conditions||Strain Background||Reference|