CLONING AND CHARACTERIZATION OF CER2, AN ARABIDOPSIS GENE THAT AFFECTS CUTICULAR WAX ACCUMULATION

Cuticular waxes are complex mixtures of very long chain fatty acids an d their derivatives that cover plant surfaces. Mutants of the ECERIFER UM2 (cer2) gene of Arabidopsis condition bright green stems and siliqu es, indicative of the relatively low abundance of the cuticular wax cr ystals that comprise the wax bloom on wild-type plants. We cloned the CER2 gene via chromosome walking. Three lines of evidence establish th at the cloned sequence represents the CER2 gene: (1) this sequence is capable of complementing the cod mutant phenotype in transgenic plants ; (2) the corresponding DNA sequence isolated from plants homozygous f or the cer2-2 mutant allele contains a sequence polymorphism that gene rates a premature stop codon; and (3) the deduced CER2 protein sequenc e exhibits sequence similarity to that of a maize gene (glossy2) that also is involved in cuticular wax accumulation. The CER2 gene encodes a novel protein with a predicted mass of 47 kD. We studied the express ion pattern of the CER2 gene by in situ hybridization and analysis of transgenic Arabidopsis plants carrying a CER2-beta-glucuronidase gene fusion that includes 1.0 kb immediately upstream of CER2 and 0.2 kb of CER2 coding sequences. These studies demonstrate that the CER2 gene i s expressed in an organ- and tissue-specific manner; CER2 is expressed at high levels only in the epidermis of young siliques and stems. Thi s finding is consistent with the visible phenotype associated with mut ants of the CER2 gene. Hence, the 1.2-kb fragment of the CER2 gene use d to construct the CER2-beta-glucuronidase gene fusion includes all of the genetic information required for the epidermis-specific accumulat ion of CER2 mRNA.