The SENSITIVE TO FREEZING2 Gene, Required for Freezing Tolerance in Arabidopsis thaliana, Encodes a (beta)-Glucosidase

The sensitive to freezing2-1 (sfr2-1) mutation causes freezing sensitivity in Arabidopsis thaliana. By mapping, transgenic complementation, and sequencing, sfr2-1 was revealed to be a mutation in gene At3g06510. A new knockout allele was obtained, and its identical freezing-sensitive phenotype confirmed that the SFR2 gene product is essential for freezing tolerance. Transcription of SFR2 was observed to be constitutive rather than stress inducible and was distributed throughout most aerial tissues. SFR2 encodes a protein homologous to family 1 glycosyl hydrolases ((beta)glycosidases), but the predicted AtSFR2 protein is divergent from all other family 1 (beta)-glycosidases of Arabidopsis, showing closer homology to the sequences of several (beta)-glycosidases from thermophilic archea and bacteria. After purification from a heterologous expression system, AtSFR2 displayed a specific hydrolytic activity against (beta)-D-glucosides.