The sensitive to freezing3 mutation of Arabidopsis thaliana is a cold-sensitive allele of homomeric acetyl-CoA carboxylase that results in cold-induced cuticle deficiencies.

The sfr3 mutation causes freezing sensitivity in Arabidopsis thaliana. Mapping, sequencing, and transgenic complementation showed sfr3 to be a missense mutation in ACC1, an essential gene encoding homomeric (multifunctional) acetyl-CoA carboxylase. Cuticle permeability was compromised in the sfr3 mutant when plants were grown in the cold but not in the warm. Wax deposition on the inflorescence stem of cold-grown sfr3 plants was inhibited and the long-chain components of their leaf cuticular wax were reduced compared with wild-type plants. Thus, freezing sensitivity of sfr3 appears, from these results, to be due to cuticular deficiencies that develop during cold acclimation. These observations demonstrated the essential role of the cuticle in tolerance to freezing and drought.

Nucleotide depletion and chloroplast division.

We have described the identification of crinkled leaves 8 (cls8) which contains a mutation within the gene encoding the large subunit of ribonucleotide reductase (RNR), the enzyme that catalyses the rate limiting step in the synthesis of deoxyribonucleotide triphosphates (dNTPs) for DNA synthesis and repair. The mutation resulted in plants with altered leaf and flower morphology, reduced root growth, bleached leaf sectors and reduced levels of dNTPs. An interesting consequence of the mutation was its effect on chloroplast division. Mutant plants had fewer, larger chloroplasts and a reduced number of chloroplast genomes compared to wild type plants. The morphological phenotype may be a consequence of altered chloroplast replication.

crinkled leaves 8--a mutation in the large subunit of ribonucleotide reductase--leads to defects in leaf development and chloroplast division in Arabidopsis thaliana.

The crinkled leaves8 (cls8) mutant of Arabidopsis thaliana displays a developmental phenotype of abnormal leaf and flower morphology, reduced root growth and bleached leaf sections. Map-based cloning identified the mutation as being within the gene encoding the large subunit of ribonucleotide reductase (RNR1), the enzyme that catalyses the rate-limiting step in the production of deoxyribonucleoside triphosphates (dNTPs) for DNA synthesis and repair. Levels of dTTP and dATP were significantly reduced in cls8. Two further mutant cls8 alleles and cls8::RNAi plants show similar or more severe phenotypes. The cls8-1 mutant has fewer copies of the chloroplast genome, and fewer, larger chloroplasts than wild-type plants. The ultrastructure of the chloroplast, however, appears normal in cls8-1 leaves. We present evidence that, under conditions of limited dNTP supply, the inhibition of chloroplast DNA replication may be the primary factor in inducing aberrant growth.