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The pattern of 1-aminocyclopropane-1-carboxylate oxidase induction in the tomato leaf petiole abscission zone is independent of expression of the ribonuclease-LX-encoding LeLX gene.

ABSTRACT: The abscission of tomato leaves occurs in the petiole abscission zone, and its late stage includes two spatially divided processes: cell separation and programmed cell death (PCD). Both of these processes are regulated by ethylene. The last step in ethylene biosynthesis is conversion of 1-aminocyclopropane-1-carboxylic acid to ethylene, which is catalysed by the enzyme 1-aminocyclopropane-1-carboxylate oxidase (ACO); however, the location of ACO in the leaf petiole abscission zone is not known. The tomato gene LeLX encodes ribonuclease LX, which is a marker for PCD and is induced by ethylene during abscission, but its association with ACO has not been explored. In a tomato transgenic line 1-7 with inhibited expression of LeLX showing delayed leaf abscission, the morphology and ultrastructure of the leaf petiole abscission zone was examined. In this zone of the cv.'VF36' and of a transgenic line 1-7, spatiotemporal differences in expression of LeACO1 and LeACO4 were analysed and ACO protein was detected immunohistochemically. In comparison to wild-type plants, there were no obvious morphological and ultrastructural features in the abscission zone of plants of a transgenic line 1-7 before and after abscission induction. LeACO1 expression was low before abscission induction, and increased 24 h after induction, although with no apparent spatial pattern. In contrast, LeACO4 was expressed before abscission induction, and its transcript level declined 24 h after induction on the distal side of the abscission zone fracture. In the LeLX-inhibited transgenic line, there were no significant differences in LeACO1 and LeACO4 expression in the petiole abscission zone, in comparison to wild-type plants. In addition, the ACO protein was immunolocalised to the vascular tissues that traverse the petiole abscission zone in plants of wild type and of a transgenic line 1-7; and additionally in the plane of future abscission zone fracture of transgenic-line plants. The results suggest temporal differential expression of the LeACO genes in tomato leaf petioles and vascular localisation of ACO1 protein. Additionally, the results indicate that expression of LeACO genes is not affected by suppression of the LeLX expression.

SUBMITTER: Chersicola M

PROVIDER: S-EPMC6032998 | biostudies-literature | 2018 Jul

REPOSITORIES: biostudies-literature

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The pattern of 1-aminocyclopropane-1-carboxylate oxidase induction in the tomato leaf petiole abscission zone is independent of expression of the ribonuclease-LX-encoding LeLX gene.

Chersicola M M Kladnik A A Tušek Žnidarič M M Lers A A Dermastia M M

Plant biology (Stuttgart, Germany) 20180426 4

The abscission of tomato leaves occurs in the petiole abscission zone, and its late stage includes two spatially divided processes: cell separation and programmed cell death (PCD). Both of these processes are regulated by ethylene. The last step in ethylene biosynthesis is conversion of 1-aminocyclopropane-1-carboxylic acid to ethylene, which is catalysed by the enzyme 1-aminocyclopropane-1-carboxylate oxidase (ACO); however, the location of ACO in the leaf petiole abscission zone is not known. ...[more]

PMID: 29633546

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Project description:Ethylene has impact on several physiological plant processes, including abscission, during which plants shed both their vegetative and reproductive organs. Cell separation and programmed cell death are involved in abscission, and these have also been correlated with ethylene action. However, the detailed spatiotemporal pattern of the molecular events during abscission remains unknown. We examined the expression of two tomato ACO genes, LeACO1, and LeACO4 that encode the last enzyme in ethylene biosynthesis, 1-aminocyclopropane-1-carboxylate oxidase (ACO), together with the expression of other abscission-associated genes involved in cell separation and programmed cell death, during a period of 0-12 h after abscission induction in the tomato flower pedicel abscission zone and nearby tissues. In addition, we determined their localization in specific cell layers of the flower pedicel abscission zone and nearby tissues obtained by laser microdissection before and 8 h after abscission induction. The expression of both ACO genes was localized to the vascular tissues in the pedicel. While LeACO4 was more uniformly expressed in all examined cell layers, the main expression site of LeACO1 was in cell layers just outside the abscission zone in its proximal and distal part. We showed that after abscission induction, ACO1 protein was synthesized in phloem companion cells, in which it was localized mainly in the cytoplasm. Samples were additionally treated with 1-methylcyclopropene (1-MCP), a competitive inhibitor of ethylene actions, and analyzed 8 h after abscission induction. Cell-layer-specific changes in gene expression were observed together with the specific localization and ethylene sensitivity of the hallmarks of cell separation and programmed cell death. While treatment with 1-MCP prevented separation of cells through inhibition of the expression of polygalacturonases, which are the key enzymes involved in degradation of the middle lamella, this had less impact on the occurrence of different kinds of membrane vesicles and abscission-related programmed cell death. In the flower pedicel abscission zone, the physical progressions of cell separation and programmed cell death are perpendicular to each other and start in the vascular tissues.

Project description:1-Aminocyclopropane-1-carboxylate (ACC) oxidase catalyses the final step in the biosynthesis of the plant hormone ethylene. The successful overexpression and characterization of active ACC oxidase from tomato has been achieved. PCR was used to insert the corrected cDNA coding for the tomato ACC oxidase into the pET-11a expression vector. Cloning of the resultant construct in Escherichia coli BL21(DE3)pLysE gave transformants which expressed ACC oxidase at levels greater than 30% of soluble protein under optimized conditions. When induced by addition of isopropyl-beta-D-thiogalactopyranoside (IPTG) at 37 degrees C the ACC oxidase expressed was less soluble and less active than when induced at 27 degrees C. The enzyme was purified to near homogeneity by a three-step chromatographic procedure. The specific activity of the purified recombinant ACC oxidase was typically 1.3-1.9 mol of ethylene/mol of enzyme per min, higher than values reported for native enzyme. Like the native enzyme it displayed a requirement for ferrous iron and ascorbate, and CO2 was an activator. The ability to discriminate between racemic diastereomers of 1-amino-2-ethyl cyclopropane-1-carboxylic acid was demonstrated. The enzyme was found to have a loose specificity for ascorbate, showing apparent preference for D-ascorbate and 5,6-O-isopropylidene L-ascorbate rather than L-ascorbate. The addition of catalase, dithiothreitol and BSA to incubation mixtures all resulted in significant increases in activity. When treated with diethylpyrocarbonate (DEPC) under mildly acidic conditions, the enzyme rapidly lost activity. Comparison of the rate of inactivation with the increase in absorbance at 240 nm gave results consistent with the modification of two to three histidine residues at the active site, although the possibility of additional modification of other nucleophilic residues cannot be excluded. Inactivation was largely prevented by the addition of substrates and ferrous iron, implying that DEPC treatment results in the modification of active-site histidines, which act as ligands for ferrous iron. CO2 offered no protection against DEPC inactivation, either in the absence or presence of substrates and/or ferrous iron.

Project description:BackgroundDetachment of plant organs occurs in abscission zones (AZs). During plant growth, the AZ forms, but does not develop further until the cells perceive abscission-promoting signals and initiate detachment. Upon signal perception, abscission initiates immediately; if there is no signal, abscission is not induced and the organ remains attached to the plant. However, little attention has been paid to the genes that maintain competence to respond to the abscission signal in the pre-abscission AZ. Recently, we found that the tomato (Solanum lycopersicum) transcription factors BLIND (Bl), GOBLET (GOB), Lateral suppressor (Ls) and a tomato WUSCHEL homologue (LeWUS) are expressed specifically in pre-abscission tissue, the anthesis pedicel AZs. To advance our understanding of abscission, here we profiled genome-wide gene expression in tomato flower pedicels at the pre-abscission stage.ResultsWe examined the transcriptomes of three tomato flower pedicel regions, the AZ and flanking proximal- (Prox) and distal- (Dis) regions, and identified 89 genes that were preferentially expressed in the AZ compared to both Prox and Dis. These genes included several transcription factors that regulate apical or axillary shoot meristem activity. Also, genes associated with auxin activity were regulated in a Prox-Dis region-specific manner, suggesting that a gradient of auxin exists in the pedicel. A MADS-box gene affecting floral transition was preferentially expressed in the Prox region and other MADS-box genes for floral organ identification were preferentially expressed in Dis, implying that the morphologically similar Prox and Dis regions have distinct identities. We also analyzed the expression of known regulators; in anthesis pedicels, Bl, GOB, Ls and LeWUS were expressed in the vascular cells of the AZ region. However, after an abscission signal, Bl was up-regulated, but GOB, Ls and LeWUS were down-regulated, suggesting that Bl may be a positive regulator of abscission, but the others may be negative regulators.ConclusionsThis study reveals region-specific gene expression in tomato flower pedicels at anthesis and identifies factors that may determine the physiological properties of the pre-abscission pedicel. The region-specific transcriptional regulators and genes for auxin activity identified here may prevent flower abscission in the absence of signal or establish competence to respond to the abscission signal.

Project description:Degenerate oligonucleotide primers corresponding to conserved regions flanking the active-site domain of 1-aminocyclopropane-1-carboxylate (ACC) synthase (EC 4.4.1.14) were used for the polymerase chain reaction (PCR) to amplify DNA fragments from mRNA isolated from tomato fruit and tomato suspension cell culture. Antibodies raised against two conserved peptide sequences (TNPSNPLGTT and SLSKDLGLPGFRVG) were used to screen for positive colonies, after the PCR products were cloned into a Bluescript plasmid and expressed in Escherichia coli. Four distinct cDNA fragments encoding ACC synthase homologs were isolated. While pBTAS1 and pBTAS4 were obtained from fruit mRNA, cell culture mRNA yielded three sequences, pBTAS1, pBTAS2, and pBTAS3. Sequencing of these gene fragments revealed that pBTAS1 and pBTAS4 were identical to those full-length sequences previously reported by Van Der Straeten et al. [Van Der Straeten, D., Van Wiemeersch, L., Goodman, H. & Van Montague, M. (1990) Proc. Natl. Acad. Sci. USA 87, 4859-4863] and Olson et al. [Olson, D. C., White, J. A., Edelman, J., Harkin, R. N. & Kende, H. (1991) Proc. Natl. Acad. Sci. USA 88, 5340-5344] from tomato fruit, whereas pBTAS2 and pBTAS3 represent new sequences. Ribonuclease protection assays were used to examine the expression of these transcripts under three different conditions of enhanced ethylene production--namely, during fruit ripening, in response to mechanical wounding in fruit tissue, and auxin stimulation in vegetative tissue. Transcripts of pBTAS1 accumulated massively during ripening and wounding but only slightly in response to auxin treatment. Although pBTAS4 was associated with fruit ripening, it was unresponsive to auxin treatment in vegetative tissue. In contrast, the expression of pBTAS2 and pBTAS3 was greatly promoted in auxin-treated vegetative tissue but was absent from fruit tissue. While the expression of pBTAS2 was moderately dependent on wounding, pBTAS3 was unresponsive to wounding. These data support the view that ACC synthase is encoded by a multigene family and that the members are differentially expressed in response to developmental, environmental, and hormonal factors.

Dataset Information

The pattern of 1-aminocyclopropane-1-carboxylate oxidase induction in the tomato leaf petiole abscission zone is independent of expression of the ribonuclease-LX-encoding LeLX gene.

Publications

The pattern of 1-aminocyclopropane-1-carboxylate oxidase induction in the tomato leaf petiole abscission zone is independent of expression of the ribonuclease-LX-encoding LeLX gene.

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