Distinctive from that of the animal system, the basic plan of the plant body is the continuous formation of a structural unit, composed of a stem with a meristem at the top and lateral organs continuously forming at the meristem. Therefore, mechanisms controlling the formation, maintenance, and development of a meristem will be a key to understanding the body plan of higher plants. Genetic analyses of filamentous flower (fil) mutants have indicated that FIL is required for the maintenance and growth of inflorescence and floral meristems, and of floral organs of Arabidopsis thaliana. FIL encodes a protein carrying a zinc finger and a HMG box-like domain, which is known to work as a transcription regulator. As expected, the FIL protein was shown to have a nuclear location. In situ hybridization clearly demonstrated that FIL is expressed only at the abaxial side of primordia of leaves and floral organs. Transgenic plants, ectopically expressing FIL, formed filament-like leaves with randomly arranged cells at the leaf margin. Our results indicate that cells at the abaxial side of the lateral organs are responsible for the normal development of the organs as well as for maintaining the activity of meristems.[Key Words: Arabidopsis; FIL; zinc finger; HMG; nuclear protein; abaxial-adaxial development]Received January 29, 1999; revised version accepted March 2, 1999.Differing from the situation in animal systems, maintenance of the meristem activity throughout life is a key for the patterning of the plant body. The shoot apical meristem and the meristem of the main root are formed in embryonic development and kept active after germination. During vegetative growth, leaves are continuously formed in a strictly controlled fashion from the shoot apical meristem. After the plant shifts to reproductive growth, the meristem converts to an inflorescence meristem, which in turn forms floral meristems. The floral meristem generates floral organs at predetermined positions. Genetic and molecular studies are under way to help understand the genetic regulatory system supporting meristem activity: control of cell division, formation of lateral organ primordia, and maintenance of the meristem structure. Recent studies using Arabidopsis, snapdragon, and maize have started to unveil the genetic basis of these molecular mechanisms (Okada and Shimura 1994).The leaf meristems are formed in a helical manner at the top of the inflorescence. When the leaf primordia begin to form, the petiole and flattened leaf blade are developed and the leaves show epinasty. Mature leaves show abaxial-adaxial polarity. The adaxial surface bears glossy, dark green epidermal cells, and produces many trichomes. On the contrary, the abaxial surface shows matte, gray-green epidermal cells and does not produce any trichomes. As the plant grows, the adaxial surface of the newly made leaves undergoes a gradual reduction in production of trichomes, and the abaxial surface starts to produce them. An Antirrhinum phantastica (phan) mutant produces filamentous leaves th...

The gene encoding a cutinase homolog, LC-cutinase, was cloned from a fosmid library of a leaf-branch compost metagenome by functional screening using tributyrin agar plates. LC-cutinase shows the highest amino acid sequence identity of 59.7% to Thermomonospora curvata lipase. It also shows the 57.4% identity to Thermobifida fusca cutinase. When LCcutinase without a putative signal peptide was secreted to the periplasm of Escherichia coli cells with the assistance of the pelB leader sequence, more than 50% of the recombinant protein, termed LC-cutinase*, was excreted into the extracellular medium. It was purified and characterized. LC-cutinase* hydrolyzed various fatty acid monoesters with acyl chain lengths of 2 to 18, with a preference for short-chain substrates (C 4 substrate at most) most optimally at pH 8.5 and 50°C, but could not hydrolyze olive oil. It lost activity with half-lives of 40 min at 70°C and 7 min at 80°C. LC-cutinase* had an ability to degrade poly(-caprolactone) and polyethylene terephthalate (PET). The specific PET-degrading activity of LC-cutinase* was determined to be 12 mg/h/mg of enzyme (2.7 mg/h/kat of pNP-butyrate-degrading activity) at pH 8.0 and 50°C. This activity is higher than those of the bacterial and fungal cutinases reported thus far, suggesting that LC-cutinase* not only serves as a good model for understanding the molecular mechanism of PET-degrading enzyme but also is potentially applicable for surface modification and degradation of PET. C utinase (EC 3.1.1.74) is a lipolytic/esterolytic enzyme that hydrolyzes not only cutin, which is a major component of plant cuticle (38), but also water-soluble esters and insoluble triglycerides (12). It hydrolyzes these substrates to carboxylic acids and alcohols through the formation of an acyl enzyme intermediate, in which the active-site serine residue is acylated by the substrate. This serine residue is located within a GXSXG sequence motif and forms a catalytic triad with His and Asp. Cutinase has been found in both fungi and bacteria. The crystal structures of two fungal cutinases from Fusarium solani f. sp. pisi (22) and Glomerella cingulata (27) have been determined. According to these structures, cutinase shares a common ␣/␤ hydrolase fold with lipase and esterase (28). However, cutinase, like esterase, does not have a lid structure, which is responsible for interfacial activation of lipase (8). Therefore, cutinase does not show interfacial activation like esterase (14). Cutinase has recently received much attention because of its potential application for surface modification and degradation of aliphatic and aromatic polyesters (16), especially polyethylene terephthalate (PET), which is a synthetic aromatic polyester composed of terephthalic acid (TPA) and ethylene glycol (10,16,36,39). However, the number of cutinases, which have been studied regarding PET modification, is still limited, and this limitation may result in the delay of the research toward the practical use of cutinases. Therefore, isolation of a novel cutinase...

The crystal structure of metagenome-derived LC-cutinase with polyethylene terephthalate (PET)-degrading activity was determined at 1.5 Å resolution. The structure strongly resembles that of Thermobifida alba cutinase. Ser165, Asp210, and His242 form the catalytic triad. Thermal denaturation and guanidine hydrochloride (GdnHCl)-induced unfolding of LC-cutinase were analyzed at pH 8.0 by circular dichroism spectroscopy. The midpoint of the transition of the thermal denaturation curve, T1/2, and that of the GdnHCl-induced unfolding curve, Cm, at 30 °C were 86.2 °C and 4.02 M, respectively. The free energy change of unfolding in the absence of GdnHCl, ΔG(H2O), was 41.8 kJ mol(-1) at 30 °C. LC-cutinase unfolded very slowly in GdnHCl with an unfolding rate, ku(H2O), of 3.28 × 10(-6) s(-1) at 50 °C. These results indicate that LC-cutinase is a kinetically robust protein. Nevertheless, the optimal temperature for the activity of LC-cutinase toward p-nitrophenyl butyrate (50 °C) was considerably lower than the T1/2 value. It increased by 10 °C in the presence of 1% polyethylene glycol (PEG) 1000. It also increased by at least 20 °C when PET was used as a substrate. These results suggest that the active site is protected from a heat-induced local conformational change by binding of PEG or PET. LC-cutinase contains one disulfide bond between Cys275 and Cys292. To examine whether this disulfide bond contributes to the thermodynamic and kinetic stability of LC-cutinase, C275/292A-cutinase without this disulfide bond was constructed. Thermal denaturation studies and equilibrium and kinetic studies of the GdnHCl-induced unfolding of C275/292A-cutinase indicate that this disulfide bond contributes not only to the thermodynamic stability but also to the kinetic stability of LC-cutinase.

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