Arabidopsis Mutants Impaired in Freezing Tolerance After Cold Acclimation

Summary

Mutations in seven different genes (SFR1—SFR7) were identified in an EMS-mutagenized collection of Arabidopsis thaliana. The sfr mutations are deleterious to freezing tolerance after cold acclimation, the phenotype being exhibited both at the whole-plant level and in the electrolyte leakage assay on excised leaves. The phenotype of each mutation was recessive or codominant, consistent with loss of function.

The sfr mutants have undergone a preliminary screen for abnormalities in their protein, carbohydrate, and fatty acid metabolism. All showed apparently normal cold-induced changes (at a gross level) in protein profiles. On the other hand, four mutations affected the cold-plus-light-induced accumulation of anthocyanin, suggesting the possibility of defects in a regulatory pathway that is in common between anthocyanin biosynthesis and one or more freezing-adaptive cold responses. One mutation (sfr4) caused a failure to accumulate sucrose during cold acclimation, which may be a sufficient cause for its sensitivity. Both the sfr4 and sfr7 mutations caused small perturbations of the fatty acid pools in leaf tissue, after cold acclimation.

We are working towards positional cloning of the SFR2 gene. Accurate mapping against physical markers (RFLPs, CAPS, SSLPs, etc.) will be possible since, in a cross between ecotypes polymorphic for such physical markers, no significant modifiers (of the sfr2 mutant’s freezing-sensitive phenotype) were found to segregate. The SFR2 gene mapped near the top of Arabidopsis thaliana chromosome 3.