Brassinolide as a modulator of the activities of cell wall loosening proteins

Abstract

Brassinolide (BR) is an essential plant hormone required for normal growth (Clouse and Sasse 1998;Li and Chory 1999;Sasse 2003). Mutations impairing in its biosynthesis or perception result in dwarfism (Schumaker and Chory 2000;Bishop 2003). Stem growth is accomplished by cell proliferation and cell expansion, and stem elongation is usually due to cell elongation. A key control part of the cell in its expansion is the cell wall. The kinetics of cell wall expansion (extension) under the steady state condition is expressed by an equation, vϭf (P-y), where v, f, P and y respectively represents the rate of cell expansion, cell wall extensibility, turgor pressure and the yield threshold of the cell wall (Lockhart 1965). The parameters, f and y are believed to be under the control of cell wall loosening proteins, f and y proteins, which are associated with the cell wall (Okamoto and Okamoto 1995). The activity of these proteins is pH-and temperature-dependent (Taguchi et al. 1999). They are most active under acidic conditions. Recently, y proteins named yieldins were isolated from Vigna unguiculata L. hypocotyls (Okamoto-Nakazato et al. 2000a) and their genes were cloned (Okamoto-Nakazato et al. 2000b). The acidic environment is thought to activate cell wall loosening enzymes including f and y proteins (Taguchi et al. 1999), resulting in cell wall loosening and hence cell wall expansion under the effective turgor pressure (P-y). Beside f and y proteins expansins are known to intimately involve in the process of cell wall expansion (Cosgrove 1998(Cosgrove , 1999(Cosgrove , 2000aCosgrove et al. 2002). The mechanisms of these cell wall loosening proteins are still enigmatic. BR has also been reported to induce cell wall loosening in pakchoi hypocotyls (Wang et al. 1993), soybean epicotyls (Zurek et al. 1994) and squash hypocotyls (Tominaga et al. 1994). Clouse (1997) has suggested that BR is involved in the modification of the cell wall through the activation of wall enzymes. Enzymes which control the modification of the cell wall have been reported to be influenced by BR (Mølhøj et al. 2002;Rose et al. 2002).We present in this paper evidence that BR is necessary for cell wall loosening and suggest that BR may act as a modulator of the activities of cell wall loosening proteins. Materials and methods Preparation of plant materialsSeeds of garden pea (Pisum sativum L., cv. Torsdag, LKB) and one of its isogenic dwarf mutants, lkb (NGB5862) were provided by Prof. T. Yokota, Teikyo University, Japan, and propagated at the former National Abstract The role of brassinolide (BR) in acid-induced cell wall loosening was studied using lkb dwarf pea (Pisum sativum L.), a BR mutant. Cell wall loosening at pH4.5 was analyzed by creep measurements of internode segments from lkb and LKB (wild type) seedlings stored in 50% glycerol at Ϫ15°C (G-segments). Although cell wall extensibility (f) was not significantly different between LKB and lkb, the yield threshold (y) was distinctly lower in LKB than in lkb, suggesting that some load-bear...

Transcription factor WRKY22 regulates canker susceptibility in sweet orange (Citrus sinensis Osbeck) by enhancing cell enlargement and CsLOB1 expression

“…Specifically, the majority of the 29 DEGs of GO:0071554 (cell wall organization and biogenesis) term, such as expansin, β-1,4-endoglucanase, pectin lyase, and cellulose synthase genes, which contribute to cell elongation and enlargement 24 – 29 , were upregulated in the overexpressing lines (Table S 3 and Table 1 ). Auxin and brassinosteroid (BR) hormones play important roles in plant cell growth 30 – 33 . Consistent with this, KEGG pathway analysis retrieved the plant hormone signal transduction pathway (cit04075) containing 20 genes (FDR < 0.05) (Fig.…”

“…The auxin-inducible genes SAUR (auxin-induced protein), GH3 (indole-3-acetic acid-amido synthetase), and IAA (auxin-responsive protein) play vital roles in regulating cell wall loosening 30 , 31 , 51 . In addition, brassinosteroids (BRs) are known to promote cell enlargement by increasing the activities of the BRU1 and TCH4 genes, that encode the xyloglucan endotransglycosylase proteins responsible for cell wall relaxation 32 , 33 . In this study, we observed that the spongy mesophyll cells of CsWRKY22 -overexpressing plants were enlarged compared with those of the WT control (Fig.…”