The cloned Eceriferum genes of Arabidopsis and the corresponding Glossy genes in maize

Recently a number of genes related to epicuticular was production in Arabidopsis thaliana or Zea mays have been isolated via map-based cloning and from tagged alleles. Of three Arabidopsis eceriferum (CER) genes cloned to date, two are of unknown function. Althrough CER1 and Glossyl (GL1) have substantial amino acid sequence similarities, they probably do not perform identical functions. The proposed decarbonylase function of CER1 is deduced from the mutant wax composition, and from its histidine-rich motifs, which are similar to other enzymes performing similar reactions. In contrast, Gl1 has fewer his-rich motifs and is more similar to membrane receptor proteins. CER2 and GL2 also share amino acid similarities. However, their functions are unknown. Analysis of mutant was compositions has provided limited information regarding the wild type functions. Indeed, the majority of cer mutants do not appear to be blocks in biosynthetic steps, but rather they have a broad affect on the wax composition. Although we have a basic understanding of was biosynthesis, we do not know the number of enzymes involved, their substrate specificities, the branch points or the substrates shared between the reductive and decarbonylation pathways. There are 21 complementation groups of Arabidopsis cer mutants, but the pathway is not saturated, and it is quite likely that many, or even most, of the 21 cer mutants are regulatory in nature. As more CER and GL genes are isolated, we must not lose sight of the need for additional biochemical studies and isolation of mutants in the biosynthetic steps.