Plant Genome IV Conference Plant Genome IV Conference
Plants are covered by an epicuticular wax (EW) layer composed of long chain lipids (C20- C40) consisting mostly of fatty acids, alcohols, esters and alkanes. The EW ultrastructure, often in crystalline form, is determined by the major wax component in the mixture. Not surprisingly this EW layer is the first line of defense against abiotic and biotic influences, like drought and frost as well as the plants interactions with pathogens and insects. There are a large variety of specific wax components which differ dramatically between plant species and contribute towards a compositional fingerprint of the plant surface which is the communication medium with other living organisms. This complex biochemical mixture of the EW can be dissected with the help of mutants, distinguished by bright green wax-free plant surfaces, affected in various steps of the biochemical pathway. Mutant analysis is also a powerful technique towards isolation of the corresponding genes, whose products are probably membrane bound and difficult to isolate biochemically. Arabidopsis is particularly suited for the isolation of the EW genes, especially as 22 loci affecting EW are already known. Biochemical compositional analysis of these mutants has enabled functions to be attributed to many of the loci. In general the biochemical steps in Arabidopsis consist of a series of elongation reactions upto C30 chain fatty acids which can be either reduced to alcohols or reduced and decarbonylated to alkanes. The complexity of the pathway and genes in plants is exemplified in barley, where over 80 genetic loci for EW are known and many developmentally regulated and minor EW products are produced. We have initiated a molecular characterization of the EW pathway in Arabidopsis. Here we report the isolation of the CER1 gene after transposon tagging with the maize En/Spm-I/dSpm system. The similarity of the CER1 protein to a group of integral membrane enzymes which process highly hydrophobic molecules, points at a function of the CER1 protein as a decarbonylase involved in decarbonylation of aldehydes to alkanes, a key step in EW biosynthesis. Database searches revealed homologues in monocots as well as dicots, which can now be separated into families with possibly related functions or enzymatic specificities. To isolate the other EW genes in Arabidopsis we have initiated directed transposon tagging with transposons that are closely linked to CER loci. Progress using this approach will be reported.