The Extensins

Tierney, Mary L.; Varner, Joseph E.

doi:10.1104/pp.84.1.1

Cited by 37 publications

(28 citation statements)

References 7 publications

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“…Other researchers (4) have found multiple bands for extensin in carrot roots. The origin and function of the different size extensin transcripts are not known, but Tierney and Varner (24) speculated that individual genes may be regulated by different environmental signals. Clearly, one of these signals for pea seedlings is low temperature.…”

Section: Resultsmentioning

confidence: 99%

Cell Wall and Extensin mRNA Changes during Cold Acclimation of Pea Seedlings

Weiser¹,

Wallner²,

Waddell³

1990

Plant Physiol.

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During exposure to 2 OC, pea (Pisum sativum) seedlings cold acclimated to a killing temperature of -6 OC. Associated with this increase in freezing resistance was an increase in the weight of cell walls and changes in wall composition. Arabinosyl content increased by 100%, while other cell wall glycosyl residues and cellulose increased by about 20%. The cell wall hydroxyproline content increased by 80%. Arabinose and hydroxyproline are both major components of the structural cell wall glycoprotein, extensin. The increase in these components indicates that the level of extensin in the cell wall increases during cold acclimation. Northern blot analysis, using the pDC5A1 genomic clone as a probe, revealed a more than three-fold increase in total extensin mRNA during exposure to cold temperature. Specific extensin transcripts of 6.0, 4.5, 3.5, 2.6, 2.3, 1.8, and 1.5 kilobases were identified. Those at 6.0, 2.6, and 1.5 kilobases were especially promoted by low temperature treatment. The rise in extensin during cold acclimation may be regulated, at least in part, at the gene level. The possible structural role of this protein in freezing protection is discussed.During extracellular freezing, plant cells are exposed to stresses associated with dehydration and consequent volume reduction, direct effects of low temperature, and mechanical effects of extracellular ice. The plasmalemma response to protoplast freeze-thaw has been characterized by Steponkus (22) A cell wall change which could significantly alter relevant mechanical properties is the increased deposition of the glycoprotein extensin, a change known to be stress induced (27). A structural role for extensin was first proposed by Lamport and Northcote (13). The glycoprotein they discovered, later named extensin for its putative role in cessation of extension growth, was found to contain a great portion of the hydroxyproline in the cell. Extensin is viewed to contribute to the strength and rigidity of the cell wall by forming an interpeptide-linked network that is separate from, but complementary to the cellulose mesh (14).It was hypothesized that if structural changes in the cell wall increase its rigidity during acclimation, thereby possibly limiting freeze-induced cell water loss and resulting injury, then an increase in freezing resistance should occur. Data presented here quantify: cell wall weight, total glucan, noncellulosic glucan, cellulose, and glycosyl content during acclimation. A pronounced increase in arabinose content led us to suspect an increase in extensin. Cell wall hydroxyproline content and extensin mRNA were measured during acclimation to test this theory. MATERIALS AND METHODSUnless otherwise indicated, the conditions for growth, acclimation, and freezing tolerance measurement were as follows. Experiments were conducted with seedlings of Pisum sativum, cultivars 'Alaska' and 'Melrose.' In most experiments, seeds were germinated and seedlings grown in the dark at 22 C, using vermiculite moistened with deionized water. In certain ca...

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Section: Resultsmentioning

confidence: 99%

Cell Wall and Extensin mRNA Changes during Cold Acclimation of Pea Seedlings

Weiser¹,

Wallner²,

Waddell³

1990

Plant Physiol.

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“…Recently there is a growing interest in the role of auxin-regulated cell wall associated proteins (O'Neill and Scott 1987). Despite the fact that plant cell walls contain, in addition to complex polysaccharides, hundreds of different proteins, glycoproteins (Roberts et al 1985), and proteoglycans (McNeil et al 1984), only the cell wall glycoprotein extensin has been cloned and studied in detail (Stafstrom and Staehelin 1987;Tierney and Varner 1987). So far, no definite conclusion has yet been reached on its possible function.…”

Section: Genes and Developmentmentioning

confidence: 99%

Carrot somatic embryogenesis depends on the phytohormone-controlled presence of correctly glycosylated extracellular proteins

1988

Genes Dev.

173

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Proteins excreted into the culture medium by carrot cells during somatic embryogenesis in the absence of 2,4-dichlorophenoxy acetic acid (2,4-D) and during unorganized cell proliferation in the presence of 2,4-D were analyzed by SDS polyacrylamide gel electrophoresis (PAGE). During somatic embryogenesis extracellular proteins with apparent molecular masses of 13, 17, 29, 38, and 46 kD were released into the medium. These proteins were reduced or absent in media of 2,4-D-grown cells. In contrast, cells grown in the presence of 2,4-D released proteins with apparent molecular masses of 27, 36, 40, 44, 48, and 72 kD. Concanavalin A staining revealed that the 29-, 46-, and 72-kD proteins as well as a doublet of 52/54-kD extracellular proteins were high-mannose type glycoproteins. Carrot cell lines impaired in somatic embryogenesis failed to release one or several of these proteins or produced aberrant forms in the absence of 2,4-D. Somatic embryogenesis in cell lines missing one or several extracellular proteins were partially restored after addition of extracellular proteins obtained from embryogenic cell lines. In contrast, cell lines producing aberrant forms of extracellular proteins could not be complemented. Somatic embryogenesis could be completely blocked by tunicamycin and deoxynojirimycin. Tunicamycin treatment resulted in the presence of deglycosylated forms of the 46-and 52/54-kD extracellular proteins; deoxynojirimycin treatment resulted in higher molecular mass forms of the 52/54-kD glycoproteins. Somatic embryogenesis in tunicamycin-blocked cultures but not in deoxynojirimycinblocked cultures could be completely rescued by addition of extracellular proteins from untreated embryo cultures. The complementing extracellular proteins were active in a narrow concentration range of 1-3 nM if a single protein was involved. The complementing activity was only found in media from embryogenic cell lines. Microscopical observation of tunicamycin-treated cells revealed that embryogenesis was affected at a very early stage, before globular stage embyros are formed. These results demonstrate that the phytohormone-controlled release of several extraceUular proteins that must be correctly glycosylated for their activity is essential for carrot somatic embryogenesis to occur.

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“…Among the cell wall proteins, hydroxyproline-rich glycoproteins (HRGPs) are probably the best characterized. The extensins, HRGP components from dicotyledonous systems (4), have been characterized at the protein, cDNA, and genomic levels. In monocotyledonous species an analogous protein rich in threonine has been identified at the protein (5-7), cDNA (8), and genomic (9) levels in maize.…”

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confidence: 99%

Accumulation of cell wall hydroxyproline-rich glycoprotein mRNA is an early event in maize embryo cell differentiation.

Ruiz-Avila

Burgess²,

Stiefel³

et al. 1992

Proc. Natl. Acad. Sci. U.S.A.

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The accumulation of the mRNA coding for a hydroxyproline-rich glycoprotein (HRGP), an abundant component of the wall from the cells of vegetative tissues, has been observed in maize embryo by in situ hybridization. The HRGP mRNA accumulates in the embryo axis and not in the scutellum and preferentially in dividing and provascular cells. The histone H4 mRNA is distributed in similar tissues but is restricted to defined groups of cells, indicating that these two gene products have a different steady-state level of accumulation during the cell cycle. The HRGP mRNA appears to be a useful marker for early formation ofthe vascular systems. The mRNA accumulation correlates in space and time with cells having a low content of cellulose in their walls, suggesting that the mRNA is produced in the early stages of cell wall formation before complete deposition of cellulose.Formation of the cell wall is an essential morphogenic event in plant cells. Different polysaccharide and protein components have been identified in the cell wall but the timing of deposition and assembly of these components is not known (1). The cell wall plays an important role in plant cell differentiation: some of its components, such as oligosaccharides, may induce specific developmental stages in tobacco thin layers (2) and a group of glycoproteins has been shown to complement mutations affecting defined steps during carrot somatic embryogenesis (3). Among the cell wall proteins, hydroxyproline-rich glycoproteins (HRGPs) are probably the best characterized. The extensins, HRGP components from dicotyledonous systems (4), have been characterized at the protein, cDNA, and genomic levels. In monocotyledonous species an analogous protein rich in threonine has been identified at the protein (5-7), cDNA (8), and genomic (9) levels in maize. Maize HRGP is a highly repetitive proline-and threonine-rich protein. Antibodies raised against the purified protein react with defined polypeptides in cell wall extracts, which have been localized in the cell wall by immunocytochemistry and immunoelectron microscopy (10,11). Previous results indicate that the Hrgp gene is active in response to different situations during cell life. The expression of the Hrgp gene parallels histone mRNA accumulation in tissues rich in dividing cells. HRGP mRNA is also found in wounded young organs (10). The mRNA coding for the maize HRGP is transiently accumulated at new vascular sites in germinating embryos, leaves, and roots (9).Tissue specificity has also been observed by immunological and Northern blot analyses in the maize embryo (11). In particular, the absence of both HRGP mRNA and protein in the scutellum has been observed. In accordance with these data, we have used a fragment of the coding region of the HRGP genomic clone as a probe to study the steps leading to formation of the cell wall in specific cell types during embryo development. We have analyzed the in situ hybridization patterns of HRGP mRNA accumulation in different stages of maize embryogenesis. The results...

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The Extensins

Cited by 37 publications

References 7 publications

Cell Wall and Extensin mRNA Changes during Cold Acclimation of Pea Seedlings

Cell Wall and Extensin mRNA Changes during Cold Acclimation of Pea Seedlings

Carrot somatic embryogenesis depends on the phytohormone-controlled presence of correctly glycosylated extracellular proteins

Accumulation of cell wall hydroxyproline-rich glycoprotein mRNA is an early event in maize embryo cell differentiation.

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