Biopolyester Membranes of Plants: Cutin and Suberin

Heterologous expression and secretion of a Streptomyces scabies esterase in Streptomyces lividans and Escherichia coli

The esterase gene from Streptomyces scabies FL1 was cloned and expressed in Streptomyces lividans on plasmids pIJ486 and pIJ702. In S. lividans, the esterase gene was expressed during later stages of growth and was regulated by zinc, as is seen with S. scabies. The 36-kDa secreted form of the esterase was purified from S. lividans. N-terminal amino acid sequencing indicated that the processing site utilized in S. lividans for the removal of the signal sequence was the same as that recognized for processing in S. scabies. Western blots (immunoblots) revealed the presence of a 40-kDa precursor form of the esterase in cytoplasmic extracts. A 23-amino-acid deletion was introduced into the putative signal sequence for the esterase. When this deleted form of the esterase was expressed in S. lividans, a cytoplasmic 38-kDa precursor protein was produced but no secreted esterase was detected, suggesting the importance of the deleted sequence for efficient processing and secretion. The esterase gene was also cloned into the pUC119 plasmid in Escherichia coli. By using the lac promoter sequence, the esterase gene was expressed, and the majority of the esterase was localized to the periplasmic space.

Cloning, sequencing, and regulation of expression of an extracellular esterase gene from the plant pathogen Streptomyces scabies

The gene that encodes the extracellular esterase produced by Streptomyces scabies has been cloned and sequenced. The gene was identified by hybridization to a synthetic oligonucleotide that corresponds to the amino-terminal amino acid sequence determined for the secreted form of the esterase. Nucleotide sequence analysis predicted a 345-amino-acid open reading frame, a putative ribosome-binding site, and 39 amino acids at the amino terminus of the sequence that is not found in the secreted protein. This 39-amino-acid sequence has many of the characteristics common to known signal peptides. End mapping the esterase transcript revealed a single 5' end of the mRNA located 51 nucleotides upstream from the start point for translation. Northern (RNA) hybridization analysis of the esterase message by using the cloned esterase gene as a probe indicated that the esterase mRNA is about 1,440 nucleotides in length and was detected only when the cells were grown in the presence of zinc. These results suggest that the level of esterase mRNA detected in the cells is regulated by zinc.

Molecular cloning, nucleotide sequence, and abscisic acid induction of a suberization-associated highly anionic peroxidase

A highly anionic peroxidase induced in suberizing cells was suggested to be the key enzyme involved in polymerization of phenolic monomers to generate the aromatic matrix of suberin. The enzyme encoded by a potato cDNA was found to be highly homologous to the anionic peroxidase induced in suberizing tomato fruit. A tomato genomic library was screened using the potato anionic peroxidase cDNA and one genomic clone was isolated that contained two tandemly oriented anionic peroxidase genes. These genes were sequenced and were 96% and 87% identical to the mRNA for potato anionic peroxidase. Both genes consist of three exons with the relative positions of their two introns being conserved between the two genes. Primer extension analysis showed that only one of the genes is expressed in the periderm of 3 day wound-healed tomato fruits. Southern blot analyses suggested that there are two copies each of the two highly homologous genes per haploid genome in both potato and tomato. Abscisic acid (ABA) induced the accumulation of the anionic peroxidase transcripts in potato and tomato callus tissues. Northern blots showed that peroxidase mRNA was detectable at 2 days and was maximal at 8 days after transfer of potato callus to solid agar media containing 10(-4) M ABA. The transcripts induced by ABA in both potato and tomato callus were identical in size to those induced in wound-healing potato tuber and tomato fruit. The anionic peroxidase peptide was detected in extracts of potato callus grown on the ABA-containing media by western blot analysis. The results support the suggestion that stimulation of suberization by ABA involves the induction of the highly anionic peroxidase.

Comparison of acetate- and pyruvate-dependent fatty-acid synthesis by spinach chloroplasts

In recent studies using intact chloroplasts of spinach (Spinacia oleracea L.) to investigate the accumulation of acetyl-CoA produced by the activity of either acetyl-CoA synthetase (EC 6.2.1.1) or the pyruvate-dehydrogenase complex, this product was not detectable. These results in combination with new information on the physiological levels of acetate and pyruvate in spinach chloroplasts (H.-J. Treede et al. 1986, Z. Naturforsch. 41 C, 733-740) prompted a reinvestigation of the incorporation of [1-(14)C] acetate and [2-(14)C] pyruvate into fatty acids at physiological concentrations.The K m for the incorporation into fatty acids was about 0.1 mM for both metabolites and thus agreed with the values obtained by H.-J. Treede et al. (1986) for acetyl-CoA synthetase and the pyruvate dehydrogenase complex. However, acetate was incorporated with a threefold higher V max. Saturation for pyruvate incorporation into the fattyacid fraction was achieved only at physiological pyruvate concentrations (<1.0 mM). The diffusion kinetics observed at higher concentrations may be the result of contamination with derivates of the labeled substrate. Competition as well as double-labeling experiments with [(3)H]acetate and [2-(14)C]pyruvate support the notion that, at least in spinach, chloroplastic acetate is the preferred substrate for fatty-acid synthesis when both substrates are supplied concurrently (P.G. Roughan et al., 1979 b, Biochem. J. 184, 565-569).Experiments with spinach leaf discs confirmed the predominance of fatty-acid incorporation from acetate. Radioactivity from [1-(14)C]acetate appeared to accumulate in glycerolipids while that from [2-(14)C]pyruvate was apparently shifted in favor of the products of prenyl metabolism.

Differential inactivation of plant lauric acid omega- and in-chain-hydroxylases by terminally unsaturated fatty acids

The microsomal fraction from Vicia sativa L. cv. Septimane contains a cytochrome P-450-dependent lauric acid omega-hydroxylase that is inactivated in a time-dependent, pseudo-first-order manner when the microsomes are incubated with 11-dodecynoic acid. The rate constant for the inactivation is approximately 4.3-4.8 X 10(-3) s-1. In contrast, the olefinic analog 11-dodecenoic acid is primarily a time-independent inhibitor of the omega-hydroxylase. 1-Aminobenzotriazole, 3-phenoxy-1-propyne, and 3-(2,4-dichlorophenoxy)-1-propyne, mechanism-based inactivators of cinnamic acid 4-hydroxylase, and 9-decenoic acid, a mechanism-based inactivator of the lauric acid in-chain hydroxylase, are at best poor inactivators of the omega-hydroxylase. Conversely, cinnamic acid 4-hydroxylase is only slightly affected by concentrations of 11-dodecynoic acid that completely inactivate the omega-hydroxylase. 11-Dodecynoic acid is thus a potent, relatively specific, inactivator of the V. sativa lauric acid omega-hydroxylase.

Cloning and sequencing of cDNA for a highly anionic peroxidase from potato and the induction of its mRNA in suberizing potato tubers and tomato fruits

A highly anionic peroxidase was strongly suggested to be involved in the deposition of the aromatic domain of suberin. cDNA containing the coding region of the suberization-associated anionic peroxidase from potato has been cloned and sequenced. The deduced amino acid sequence of the peroxidase shows that it is an anionic protein with considerable homology to other peroxidases. The amino acid sequence of two tryptic peptides obtained from the anionic peroxidase purified from suberizing potato tuber slices matched exactly with two segments of the amino acid sequence deduced from the nucleotide sequence of the cloned cDNA. The identity of the cloned cDNA is further supported by hybrid-selected translation and immunological recovery of the product with antibodies prepared against the purified anionic peroxidase. This anionic peroxidase was barely detectable at 2 days after wounding, and reached a maximal level at 8 days after wounding. Using the cDNA for the anionic peroxidase as a probe, we showed that the mRNA for the enzyme was induced in suberizing potato. The mRNA levels increased from an undetectable level in control tuber tissue to a maximal level in suberizing tuber tissue aged for four days. In suberizing tomato fruit the peroxidase mRNA showed induction and the level reached a maximum in three days. Ine data suggest that the induction of the peroxidase by wounding is preceded by transcriptional activation of the peroxidase gene or by increased stabilization of the mRNA. The time course of increase in mRNA for the anionic peroxidase was consistent with its postulated role in suberization.

Purification and characterization of a novel extracellular esterase from pathogenic Streptomyces scabies that is inducible by zinc

Native polyacrylamide gels of extracellular proteins produced by several Streptomyces isolates grown with suberin were assayed in situ for esterase activity. Two pathogenic isolates of Streptomyces scabies from different geographical regions were found to produce a similar esterase activity that was not produced by nonpathogenic strains. After treatment with EDTA, suberin no longer induced esterase production. Expression was restored when EDTA-treated suberin was supplemented with zinc. The optimal concentration of zinc required for esterase production was 2 microM. This esterase was purified from one of the pathogenic isolates and characterized. The enzyme was 38,000 daltons when determined by gel filtration on Sephadex G-100 and 36,000 daltons when determined by denaturing polyacrylamide gel electrophoresis. The esterase showed maximal activity in sodium phosphate buffer above pH 8.0, was stable to temperatures of up to 60 degrees C, and had an apparent Km of 125 microM p-nitrophenyl butyrate.

Discovery of a cutinase-producing Pseudomonas sp. cohabiting with an apparently nitrogen-fixing Corynebacterium sp. in the phyllosphere

A phyllospheric bacterial culture, previously reported to partially replace nitrogen fertilizer (B. R. Patti and A. K. Chandra, Plant Soil 61:419-427, 1981) was found to contain a fluorescent pseudomonas which was identified as Pseudomonas putida and a Corynebacterium sp. The P. putida isolate was found to produce an extracellular cutinase when grown in a medium containing cutin, the polyester structural component of plant cuticle. The Corynebacterium sp. grew on nitrogen-free medium but could not produce cutinase under any induction conditions tested, whereas P. putida could not grow on nitrogen-free medium. When cocultured with the nitrogen-fixing Corynebacterium sp., the P. putida isolate grew in a nitrogen-free medium, suggesting that the former provided fixed N2 for the latter. These results suggest that the two species coexist on the plant surface, with one providing carbon and the other providing reduced nitrogen for their growth. The presence of cutin in the medium induced cutinase production by P. putida. However, unlike the previously studied fungal systems, cutin hydrolysate did not induce cutinase. Thin-layer chromatographic analysis of the products released from labeled apple fruit cutin showed that the extracellular enzyme released all classes of cutin monomers. This enzyme also catalyzed hydrolysis of the model ester substrates, p-nitrophenyl esters of fatty acids, and optimal conditions were determined for a spectrophotometric assay with p-nitrophenyl butyrate as the substrate. It did not hydrolyze triacyl glycerols, indicating that the cutinase activity was not due to a nonspecific lipase. It showed a broad pH optimum between 8.0 and 10.5 with 3H-labeled apple cutin as the substrate.(ABSTRACT TRUNCATED AT 250 WORDS)

Purification and characterization of the NADPH-cytochrome P-450 (cytochrome c) reductase from higher-plant microsomal fraction

NADPH-cytochrome P-450 (cytochrome c) reductase (EC 1.6.2.4) was solubilized by detergent from microsomal fraction of wounded Jerusalem-artichoke (Helianthus tuberosus L.) tubers and purified to electrophoretic homogeneity. The purification was achieved by two anion-exchange columns and by affinity chromatography on 2',5'-bisphosphoadenosine-Sepharose 4B. An Mr value of 82,000 was obtained by SDS/polyacrylamide-gel electrophoresis. The purified enzyme exhibited typical flavoprotein redox spectra and contained equimolar quantities of FAD and FMN. The purified enzyme followed Michaelis-Menten kinetics with Km values of 20 microM for NADPH and 6.3 microM for cytochrome c. In contrast, with NADH as substrate this enzyme exhibited biphasic kinetics with Km values ranging from 46 microM to 54 mM. Substrate saturation curves as a function of NADPH at fixed concentration of cytochrome c are compatible with a sequential type of substrate-addition mechanism. The enzyme was able to reconstitute cinnamate 4-hydroxylase activity when associated with partially purified tuber cytochrome P-450 and dilauroyl phosphatidylcholine in the presence of NADPH. Rabbit antibodies directed against plant NADPH-cytochrome c reductase affected only weakly NADH-sustained reduction of cytochrome c, but inhibited strongly NADPH-cytochrome c reductase and NADPH- or NADH-dependent cinnamate hydroxylase activities from Jerusalem-artichoke microsomal fraction.

Primary structure of the active site region of fungal cutinase, an enzyme involved in phytopathogenesis

Cutinase, a fungal extracellular enzyme involved in phytopathogenesis, was labeled by treatment with [3H]diisopropylfluorophosphate and by reduction of the only disulphide with dithioerythritol followed by treatment with iodo[1-14C]acetamide. A tryptic peptide containing both the active serine and one of the cys involved in the disulphide bridge was isolated and the primary structure was determined to be: Glu-Met-Leu-Gly-Leu-Phe-Gln-Gln-Ala-Asn-Thr-Lys-Cys-Pro-Asp-Ala-Thr-Leu-Ile-Ala - Gly-Gly-Tyr-Ser-Gln-Gly-(Ala)-Ala-Leu-Ala. This active site has very little homology with the active serine containing regions of other enzymes.

Composition and ultrastructure of the suberized cell wall of isolated crystal idioblasts from Agave americana L. leaves

Styloid-calcium-oxalate-crystal-containing idioblasts possess an interior cell-wall layer which has a lamellar ultrastructure. Idioblasts were isolated by centrifugation of an Agave americana leaf homogenate through 2M sucrose. The aliphatic monomers of the polymeric material from an idioblast fraction were primarily ω-hydroxy acids (32%) and dicarboxylic acids (35%), with C18:1 dicarboxylic acid being the most dominant monomer (25%). Nitrobenzene oxidation of the idioblasts yielded syringaldehyde and vanillin in a ratio of 0.46:1. The major class of wax associated with the idioblasts was free fatty acids (34%). A major homologue of both the fatty acid and fatty alcohol fractions of this wax was C22. The hydrocarbon fraction of the wax had a broad chainlength distribution with a large amount of even-numbered (47%) and shorter-chain homologues. The ultrastructure, the composition of the aliphatic and aromatic components of the polymeric material as well as the composition of the wax show that the idioblast cell wall is suberized. The wax and cutin polymer of the epidermis of A. americana leaves were chemically characterized for comparative purposes.

Mechanism of action of cutinase: chemical modification of the catalytic triad characteristic for serine hydrolases

Cutinase from Fusarium solani f. sp. pisi was inhibited by diisopropyl fluorophosphate and phenylboronic acid, indicating the involvement of an active serine residue in enzyme catalysis. Quantitation of the number of phosphorylated serines showed that modification of one residue resulted in complete loss of enzyme activity. One essential histidine residue was modified with diethyl pyrocarbonate. This residue was buried in native cutinase and became accessible to chemical modification only after unfolding of the enzyme by sodium dodecyl sulfate. The modification of carboxyl groups with 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide in the absence of sodium dodecyl sulfate did not result in inactivation of the enzyme; however, such modifications in the presence of sodium dodecyl sulfate resulted in complete loss of enzyme activity. The number of residues modified was determined by incorporation of [14C]glycine ethyl ester. Modification of cutinase in the absence of sodium dodecyl sulfate and subsequent unfolding of the enzyme with detergent in the presence of radioactive glycine ester showed that one buried carboxyl group per molecule of cutinase resulted in complete inactivation of the enzyme. Three additional peripheral carboxyl groups were modified in the presence of sodium dodecyl sulfate. Carbethoxylation of the essential histidine and subsequent incubation with the esterase substrate p-nitrophenyl [1-14C]acetate revealed that carbethoxycutinase was about 10(5) times less active than the untreated enzyme. The acyl-enzyme intermediate was stabilized under these conditions and was isolated by gel permeation chromatography. The results of the present chemical modification study indicate that catalysis by cutinase involves the catalytic triad and an acyl-enzyme intermediate, both characteristic for serine proteases.

Fine structure of plant cuticles in relation to water permeability: The fine structure of the cuticle of Clivia miniata reg. leaves

The fine structure of the upper cuticular membrane (CM) of Clivia miniata leaves was investigated using electron microscopy. The CM is made up of a thin (130 nm) lamellated cuticle proper (CP) and a thick (up to 7 μm over periclinal walls) cuticular layer (CL) of marbled appearance. Evidence is presented to show that the electron lucent lamellae of the CP do not simply represent layers of soluble cuticular lipids (SCL). Instead, the lamellation is probably due to layers of cutin differing in polarity. It is argued that the SCL in the Cp are the main barrier to water. Thickening of the CM during leaf development takes place by interposition of cutin between the CM and the cellin wall. The cutin of young, expanding leaves has a high affinity for KMnO4 and is therefore relatively polar. As leaves mature, the external CL underneath the CP becomes non-polar, as only little contrast can be obtained with permanganate as the post fixative.

Freeze-fracture observations on the plasma membrane, the cell wall and the cuticle of growing protonemata of Adiantum capillus-veneris L

Using freeze-fracture electron microscopy we have examined the morphology of the plasma membrane and the cell wall of single-celled protonemal filaments of the fern Adiantum capillus-veneris grown under continuous red light. The surface of the protonemal cell wall is completely covered by a multilayered, lipid-like coat, probably consisting of cuticular waxes. The rhizoid seems to lack this type of coat. The cell walls of the protonemata contain 8-nm thick, randomly oriented fibrils. In rapidly growing protonemata the P-face of the plasma membrane contains both randomly distributed particles and distinct particle rosettes. The rosettes consist of six 8-9-nm-wide particles in a ring-like configaration and have an outer diameter of 24 nm. They closely resemble the particle rosettes seen on the P-face of the plasma membrane of green algae and of higher plants, which recently have been implicated in the synthesis of cellulose fibrils. Within 20 μm from the tip of the protonemata, and coinciding with the region of maximal cell-wall growth and expansion and thus cellulose-fibril synthesis, the greatest density of rosettes (20/μm(2)) is observed. Beyond 20 μm from the tip this number drops rapidly to near zero at 50 μm. The rosettes have a tendency to form small, irregular clusters, but only very rarely are three or more rosettes found in a row or in a geometrical pattern. Our measurements of the size and the density of the randomly distributed plasma membrane particles indicate that the tip region must be specialized with respect to other plasma-membrane activities as well. Thus the tip region contains not only the highest density of randomly destributed intramembrane particles, but also particles of different sizes than those found elsewhere in the plasma membrane.

Composition, ultrastructure and function of the cutin- and suberin-containing layers in the leaf, fruit peel, juice-sac and inner seed coat of grapefruit (Citrus paradisi Macfed.)

Cutin and suberin polymers from various anatomical regions of grapefruit were analyzed chemically and ultrastructurally. The leaf, fruit peel and juice-sac showed an amorphous cuticular layer. The cutin in the leaf was composed of 10,16-dihydroxy C16 acid and its positional isomers as the major monomers whereas 16-hydroxy-10-oxo C16 acid was a major component in the fruit peel. Juice-sac cutin, on the other hand, contained the dihydroxy C16 acids, hydroxyoxo C16 acids, hydroxyepoxy C18 acids and trihydroxy C18 acids. Ultrastructural examination of the inner seed coat showed that an amorphous cuticular layer encircled the entire seed except in the chalazal region which showed several layers of cells with lamellar suberin structure throughout the cell walls. Consistent with the ultrastructural assignment, the compositions of the aliphatic components of the polymers from the chalazal region and the non-chalazal region indicated the presence of suberin and cutin, respectively. The aliphatic portion of the polymer from the chalazal region of the inner seed coat contained C16, C18:1, C22 and C24 ω-hydroxy acids (46% combined total) and the corresponding dicarboxylic acids (43%) as the major components. ω-Hydroxy-9,10-epoxy C18 acids and 9,10,18-trihydroxy C18 acids were the major components (77%) of the polymer from the non-chalazal portion of the inner seed coat. The main portion and the chalazal region of the inner seed coat yielded 17 and 342 μg/cm(2) of aliphatic monomers, respectively, and the diffusion resistance of these two portions of the inner seed coat were 62 and 192 sec/cm, respectively. The inner seed coat was shown to be the major moisture diffusion barrier influencing imbibition and germination.