Accumulation of Small Heat-Shock Protein Homologs in the Endoplasmic Reticulum of Cortical Parenchyma Cells in Mulberry in Association with Seasonal Cold Acclimation1

Abstract

Cortical parenchyma cells of mulberry (Morus bombycis Koidz.) trees acquire extremely high freezing tolerance in winter as a result of seasonal cold acclimation. The amount of total proteins in endoplasmic reticulum (ER)-enriched fractions isolated from these cells increased in parallel with the process of cold acclimation. Protein compositions in the ER-enriched fraction also changed seasonally, with a prominent accumulation of 20-kD (WAP20) and 27-kD (WAP27) proteins in winter. The N-terminal amino acid sequence of WAP20 exhibited homology to ER-localized small heat-shock proteins (smHSPs), whereas that of WAP27 did not exhibit homology to any known proteins. Like other smHSPs, WAP20 formed a complex of high molecular mass in native-polyacrylamide gel electrophoresis. Furthermore, not only WAP20 but also 21-kD proteins reacted with antibodies against WAP20. Fractionation of the crude microsomes by isopycnic sucrose-gradient centrifugation revealed that both WAP27 and WAP20 were distributed on a density corresponding to the fractions with higher activity of ER marker enzyme, suggesting localization of these proteins in the ER. When ERenriched fractions were treated with trypsin in the absence of detergent, WAP20 and WAP27 were undigested, suggesting localization of these proteins inside the ER vesicle. The accumulation of a large quantity of smHSPs in the ER in winter as a result of seasonal cold acclimation indicates that these proteins may play a significant role in the acquisition of freezing tolerance in cortical parenchyma cells of mulberry trees.

Up-regulation of heat shock proteins is essential for cold survival during insect diapause

“…Hsp expression is strongly up-regulated during dormancies ranging from encystment in the brine shrimp, Artemia franciscana (33), and the quiescent stages of the freshwater sponge, Spongilla lacustris (34), to mammalian hibernation (35,36), and small Hsps are up-regulated during dormancy in a number of plant tissues including seeds (37-39), parenchyma cells (40), and bark tissue (41). Additionally, polar organisms including larvae of the terrestrial Antarctic midge, Belgica antarctica (42), an Antarctic fish, Trematomus bernacchii, (43), and an Antarctic marine ciliate, Euplotes focardii (44), continuously express Hsps.…”

Analysis of expressed sequence tags from Musa acuminata ssp. burmannicoides, var. Calcutta 4 (AA) leaves submitted to temperature stresses

“…These changes include: (1) modifications in the composition of the plasma membranes (Uemura et al 1995); (2) intracellular accumulation of compatible osmolytes, such as soluble sugars, prolines and betaines (Hare et al 1998), HSPs (Ukaji et al 1999) and cold-regulated (COR) proteins (Thomashow 1999); (3) extracellular accumulation of antifreeze proteins (Griffith and Antikainen 1996); (4) changes in the properties of the cell walls (Fujikawa and Kuroda 2000). These changes have been found to be associated with increased freezing tolerance (Thomashow 1999).…”

Trypsin-Sensitive Modulation of Intestinal Epithelial MD-2 as Mechanism of Lipopolysaccharide Tolerance

“…Equal aliquots of the digestion mixture were withdrawn at different time points, transferred to a tube containing LPS-free 1ϫ trypsin inhibitor, and separated by (MES) SDS-PAGE. Digestion of SW480-microsomal fraction was performed in the presence or absence of 0.1 g/l trypsin with 0.3% Triton X-100 at 4°C for 60 min (30). For digestion with Endo H, microsomal fraction was denatured, as previously described (31).…”