The glossy1 Locus of Maize and an Epidermis-Specific cDNA from Kleinia odora Define a Class of Receptor-Like Proteins Required for the Normal Accumulation of Cuticular Waxes

Abstract

Mutations at the glossyl (gll) locus of maize (Zea mays L.) quantitatively and qualitatively affect the deposition of cuticular waxes on the surface of seedling leaves. l h e gll locus has been molecularly cloned by transposon tagging with the Mutafor transposon system. l h e epi23 cDNA was isolated by subtractive hybridization as an epidermis-specific mRNA from Senerio odora (Kleinia odora). l h e deduced amino acid sequence of the GL1 and EP123 proteins are very similar to each other and to two other plant proteins i n which the sequences were deduced from their respective mRNAs. These are the Arabidopsis CERl protein, which is involved in cuticular wax deposition on diques, stems, and leaves of that plant, and the protein coded by the rice expressed sequence tag RICS2751A. All four proteins are predicted to be localized in a membrane via a common NH,-terminal domain, which consists of either five or seven membrane-spanning helices. l h e COOHterminal portion of each of these proteins, although less conserved, is predicted to be a water-soluble, globular domain. These sequence similarities indicate that these plant orthologs may belong to a superfamily of membrane-bound receptors that have been extensively characterized from animals, including the HIV co-receptor fusin (also termed CXCR4).The cuticle is the outermost interface between a plant and its environment, and as such plays a crucial role in the plant's survival (Martin and Juniper, 1970; Kolattukudy, 1981). It consists of cutin embedded in a complex mixture of lipids commonly referred to as the cuticular waxes. Cutin is a polymer of fatty acid derivatives such as w-, di-, and trihydroxy and hydroxy epoxy fatty acids and dicarboxylic fatty acids. These monomers are polymerized by * This work was supported in part by National Science Foundation grant nos. IBN-9316832 intermonomeric ester linkages. Cuticular waxes are a complex mixture of lipids, including hydrocarbons (n-alkanes, branched alkanes, cyclic alkanes, and alkenes), ketones, ketols, alcohols, aldehydes, diols, acids, and esters. The majority of the lipid compounds in the cuticle are derived from cellular fatty acids (for reviews, see Kolattukudy and Walton, 1973; Kolattukudy et al., 1976;Tulloch, 1976; Kolattukudy, 1980). Early biochemical investigations have identified reactions by which many of the various components of the cuticular wax are synthesized (Kolattukudy and Walton, 1973; Kolattukudy et al., 1976;Tulloch, 1976; Kolattukudy, 1980). However, the isolation and characterization of enzymes postulated to be involved in these processes has been technically difficult to achieve because plant epidermal tissue, the site of cuticular wax biosynthesis (Kolattukudy et al., 1976), is difficult to obtain in large quantities. To overcome t h s technical barrier, a molecular genetic approach was taken to isolate a gene involved in cuticular wax biosynthesis. Using the Mutator transposon system, we have cloned the gIossy2 locus of maize (Zea mays L.) via transposon tagging (Chandler and Hard...

Cloning and Characterization of the WAX2 Gene of Arabidopsis Involved in Cuticle Membrane and Wax Production

“…In contrast to cer1, the stems of wax2 are deficient in both aldehydes and alkanes (and its metabolites), suggesting that wax2's primary blockage ( Figure 10) occurs in the metabolic step preceding that blocked by cer1. Conversely, Hansen et al (1997) suggested that the homologous GL1 could not code for a decarbonylase because Phylogram derived from a data set of deduced polypeptides for Arabidopsis WAX2 and related deduced polypeptides. The rooted tree was constructed using CLUSTAL W (Thompson et al, 1994).…”

“…the gl1 mutant actually had higher proportions of alkanes than the wild-type parent and the GL1 protein lacked the third Hisrich motif required for iron binding. Instead, based on the predicted secondary structure of GL1 and CER1, Hansen et al (1997) suggested that these proteins might belong to a superfamily of integral membrane receptors that are composed of a hydrophobic N-terminal domain with seven transmembrane-spanning regions and a globular water-soluble C-terminal domain (Probst et al, 1992). Although WAX2, CER1, and GL1 have comparable transmembrane structures, our analysis using Sequence BLAST and multiple alignments using CLUSTAL W 1.82 did not show high similarity to membrane receptors.…”

“…WAX2 protein had highest sequence similarities to a partial Senecio odora cDNA clone named epi23 (Hansen et al, 1997) and a partial rice sequence annotated as a GLOSSY1 homolog (Hansen et al, 1997), with 65 and 63% amino acid identity, respectively ( Figure 4). WAX2 has 35% amino acid identity to GLOSSY1 in maize (Hansen et al, 1997) and 34% amino acid identity to CER1 in Arabidopsis (Aarts et al, 1995). WAX2 amino acid identity to three other CER1-like paralogs in Arabidopsis varied between 31 and 34%.…”

“…Four of these-CER2 , CER3 , GL2 , and GL15 -appear to encode regulatory loci (Tacke et al, 1995;Hannoufa et al, 1996;Moose and Sisco, 1996;Negruk et al, 1996;Xia et al, 1996), three-CER6 , KCS1 , and GL8 -may encode metabolic enzymes (Xu et al, 1997;Millar et al, 1999;Todd et al, 1999;Fiebig et al, 2000), and two-CER1 and GL1 -may be involved in either the transport or the metabolism of wax compounds (Aarts et al, 1995;Hansen et al, 1997). None of these genes has been associated with cuticle membrane synthesis.…”

CUT1, an Arabidopsis Gene Required for Cuticular Wax Biosynthesis and Pollen Fertility, Encodes a Very-Long-Chain Fatty Acid Condensing Enzyme

“…Based on the wax composition of the cer1 mutants (Hannoufa et al, 1993) and the histidine-rich motifs of the protein sequence (Aarts et al, 1995), CER1 has been proposed to encode an aldehyde decarbonylase. However, other possible functions for CER1 have been suggested (Hansen et al, 1997). The CER2 gene is likely to encode a biosynthetic enzyme, because it shares sequence similarity with acyl transferases (St-Pierre et al, 1998).…”