The CER22 gene required for the synthesis of cuticular wax alkanes in Arabidopsis thaliana is allelic to CER1.

Cuticular waxes coat the primary aerial tissues of land plants and serve as a protective barrier against non-stomatal water loss and various environmental stresses. Alkanes are the most prominent cuticular wax components and are thought to have an important role in controlling permeability of the cuticle. However, alkane biosynthesis in plants is not well understood. Arabidopsis eceriferum1 (cer1) and cer22 mutants show dramatic reductions in alkane, secondary alcohol, and ketone content, and concomitant increases in aldehyde content, suggesting that one or both of these genes encode an alkane-forming enzyme. To determine the biochemical identity of CER22, and to investigate the relationship between CER1 and CER22 in alkane formation, we mapped the cer22 mutation as a first step to positional cloning. Unexpectedly, mapping revealed linkage of cer22 to markers on chromosome 1 in the vicinity of CER1, and not to markers on chromosome 3 as previously reported. Failure of the cer1-1 and cer22 mutants to complement each other, and the presence of an allele specific mutation in the CER1 gene amplified from cer22 genomic DNA demonstrated that CER22 is identical to CER1. The cer22 mutant was therefore renamed cer1-6. Analyses of CER1 transcript levels, and stem cuticular wax load and composition in the cer1-6 (cer22) line indicated that cer1-6 is a weak mutant allele of CER1. This represents an important step forward in our understanding of alkane synthesis in plants, and will direct future research in the field to focus on the role of CER1 in this process.