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Title: Regulation of plant cells, cell walls and development by mechanical signals

Abstract

The overall goal of the revised scope of work for the final year of funding was to characterize cell wall biosynthesis in developing cotyledons and in the shoot apical meristem of Arabidopsis thaliana, as a way of learning about developmental control of cell wall biosynthesis in plants, and interactions between cell wall biosynthesis and the microtubule cytoskeleton. The proposed work had two parts – to look at the effect of mutation in the SPIRAL2 gene on microtubule organization and reorganization, and to thoroughly characterize the glycosyltransferase genes expressed in shoot apical meristems by RNA-seq experiments, by in situ hybridization of the RNAs expressed in the meristem, and by antibody staining of the products of the glycosyltransferases in meristems. Both parts were completed; the spiral2 mutant was found to speed microtubule reorientation after ablation of adjacent cells, supporting our hypothesis that reorganization correlates with microtubule severing, the rate of which is increased by the mutation. The glycosyltransferase characterization was completed and published as Yang et al. (2016). Among the new things learned was that primary cell wall biosynthesis is strongly controlled both by cell type, and by stage of cell cycle, implying not only that different, even adjacent, cells can havemore » different sugar linkages in their (nonshared) walls, but also that a surprisingly large proportion of glycosyltransferases is regulated in the cell cycle, and therefore that the cell cycle regulates wall maturation to a degree previously unrecognized.« less

Authors:
 [1]
  1. California Inst. of Technology (CalTech), Pasadena, CA (United States)
Publication Date:
Research Org.:
California Inst. of Technology (CalTech), Pasadena, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1302424
Report Number(s):
DOE-CALTECH-13873
DOE Contract Number:
FG02-88ER13873
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES

Citation Formats

Meyerowitz, Elliot M. Regulation of plant cells, cell walls and development by mechanical signals. United States: N. p., 2016. Web. doi:10.2172/1302424.
Meyerowitz, Elliot M. Regulation of plant cells, cell walls and development by mechanical signals. United States. doi:10.2172/1302424.
Meyerowitz, Elliot M. 2016. "Regulation of plant cells, cell walls and development by mechanical signals". United States. doi:10.2172/1302424. https://www.osti.gov/servlets/purl/1302424.
@article{osti_1302424,
title = {Regulation of plant cells, cell walls and development by mechanical signals},
author = {Meyerowitz, Elliot M.},
abstractNote = {The overall goal of the revised scope of work for the final year of funding was to characterize cell wall biosynthesis in developing cotyledons and in the shoot apical meristem of Arabidopsis thaliana, as a way of learning about developmental control of cell wall biosynthesis in plants, and interactions between cell wall biosynthesis and the microtubule cytoskeleton. The proposed work had two parts – to look at the effect of mutation in the SPIRAL2 gene on microtubule organization and reorganization, and to thoroughly characterize the glycosyltransferase genes expressed in shoot apical meristems by RNA-seq experiments, by in situ hybridization of the RNAs expressed in the meristem, and by antibody staining of the products of the glycosyltransferases in meristems. Both parts were completed; the spiral2 mutant was found to speed microtubule reorientation after ablation of adjacent cells, supporting our hypothesis that reorganization correlates with microtubule severing, the rate of which is increased by the mutation. The glycosyltransferase characterization was completed and published as Yang et al. (2016). Among the new things learned was that primary cell wall biosynthesis is strongly controlled both by cell type, and by stage of cell cycle, implying not only that different, even adjacent, cells can have different sugar linkages in their (nonshared) walls, but also that a surprisingly large proportion of glycosyltransferases is regulated in the cell cycle, and therefore that the cell cycle regulates wall maturation to a degree previously unrecognized.},
doi = {10.2172/1302424},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2016,
month = 6
}

Technical Report:

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  • Plants regulate water loss and CO{sub 2} gain by modulating the aperture sizes of stomata that penetrate the epidermis. Aperture size itself is increased by osmolyte accumulation and consequent turgor increase in the pair of guard cells that flank each stoma. Guard-cell phosphoenolpyruvate carboxylase, which catalyzes the regulated step leading to malate synthesis, is crucial for charge and pH maintenance during osmolyte accumulation. Regulation of this cytosolic enzyme by effectors is well documented, but additional regulation by posttranslational modification is predicted by the alteration of PEPC kinetics during stomatal opening. In this study, the authors have investigated whether this alterationmore » is associated with the phosphorylation status of this enzyme. Using sonicated epidermal peels (isolated guard cells) pre-loaded with {sub 32}PO{sub 4}, the authors induced stomatal opening and guard-cell malate accumulation by incubation with 5 {micro}M fusicoccin (FC). In corroboratory experiments, guard cells were incubated with 5 {micro}M fusicoccin (FC). In corroboratory experiments, guard cells were incubated with the FC antagonist, 10 {micro}M abscisic acid (ABA). The phosphorylation status of PEPC was assessed by immunoprecipitation, electrophoresis, immunoblotting, and autoradiography. PEPC was phosphorylated when stomata were stimulated to open, and phosphorylation was lessened by incubation with ABA.« less
  • At various times after pulse labeling Vicia faba L. leaflets with {sup 14}CO{sub 2}, whole-leaf pieces and rinsed epidermal peels were harvested and subsequently processed for histochemical analysis. Cells dissected from whole leaf retained apoplastic contents whereas those from rinsed peels contained only cytoplastic contents. Sucrose specific radioactivity peaked in palisade cells, 111 GBq{center_dot}mol{sup {minus}1}, at 20 min. In contrast, the {sup 14}C content and sucrose specific radioactivity were very low in guard cells for 20 min, implying little CO{sub 2} incorporation; both then peaked at 40 min. The guard-cell apoplast had a high maximum sucrose specific radioactivity and amore » high sucrose influx rate. These and other comparisons implied the presence of (a) multiple sucrose pools in mesophyll cells, (b) a localized mesophyll-apoplast region that exchanges with phloem and stomata, and (c) mesophyll-derived sucrose in guard-cell walls sufficient to diminish stomatal opening by {approximately} 4 {micro}m. Factors expected to enhance sucrose accumulation in guard-cell walls are (a) high transpiration rate, which closes stomata, and (b) high apoplastic sucrose concentration, which is elevated when mesophyll-sucrose efflux exceeds translocation. Therefore, multiple physiological factors are integrated in the attenuation of stomatal-aperture size by this previously unrecognized mechanism.« less
  • The most important accomplishment was the discovery that oligosaccharides derived from plant cell wall polysaccharides are biolgically active, that is, they possess a regulatory role in plants. The connection between biologically active carbohydrates and plant cell walls came with the discovery that bacteria elicit the accumulation of phytoalexins in plant tissues by injuring plant cells and, in doing so, cause the release of a fragment of a plant cell wall polysaccharide that elicits the synthesis of phytoalexins. The second biologically active carbohydrate found in plant cell walls was also found to be a pectic polysaccharide. In this case, the carbohydratemore » is a regulatory molecule that induces the de novo synthesis of proteins possessing the ability to inhibit proteinases of insects and bacteria. Naturally occurring carbohydrates with biological regulatory functions are called oligosaccharins. It appears that the endogenous elicitor and the proteinase inhibitor-inducing factor are just two examples of a variety of oligosaccharins with diverse functions are known including a nonasaccharide fragment that inhibits elongation of pea-stem segments, an oligosaccharin capable of inhibiting completely the flowering of Lemna, and oligosaccharin involved in the hypersensitive resistance response of plants to incompatible races of pathogens. Evidence for several other oligosaccharins has been obtained. (ERB)« less
  • Studies included: (1) advances in the ability to structurally characterize complex carbohydrates; (2) the structural characterization of cell wall polysaccharides; (3) the structural analysis of polysaccharides secreted by rhizobia; (4) the characterization of the hepta-..beta..-glucoside elicitor of phytoalexins; (5) characterization of oligosaccharins; (6) new assays for oligosaccharins and oligosaccharia-releasing enzymes; (7) characterization of the enzymes produced by the pathogen Pyricularia to degrade its host's cell walls; and (8) isolation of strains of Pyriculeria. (ACR)