Heat Shock Causes Selective Destabilization of Secretory Protein mRNAs in Barley Aleurone Cells

Abstract

The aleurone layer of GA3-stimulated barley (Hordeum vulgare L., cv Himalaya) grains is normally devoted to the synthesis and secretion of hydrolytic enzymes. Heat shock, however, suppresses the synthesis of the main hydrolytic enzyme, a-amylase, by destabilizing its otherwise highly stable mRNA (FC Belanger, MR Brodl, T-hD Ho [1986] Proc Natd Acad Sci USA 83: 1354-1358. In this paper we document that heat shock causes the suppression of the synthesis of some normal cellular proteins, while the synthesis of other normal cellular proteins is unaffected by heat shock. There are two major isozymic forms of a-amylase encoded by distinct mRNAs. The mRNA levels for both isozymic forms and the mRNA levels of two other secretary proteins, a protease and an endochitinase, were markedly reduced during heat shock. However, the levels of actin and j-tubulin mRNAs, both nonsecretory proteins, were not diminished during heat shock. In addition, the levels of three other mRNA species detected by a set of unidentified cDNA clones (the sequence of one shows that it lacks a signal sequence) remained unchanged during heat shock. These data indicate that there are two classes of normal cellular protein mRNAs with regard to the effect of heat shock upon their persistence in the cell, and suggest that the distinction between them is whether or not they encode secretary proteins.Heat shock is, quite simply, a transient elevation in temperature, usually about 10 to 15oC above ambient temperature. This simple manipulation produces remarkable changes in gene expression. In every organism tested to date heat shock induces the synthesis of a characteristic set of proteins, the so-called hsps3 ( There is a translational bias established during heat shock that favors the translation of the newly transcribed hsp mRNAs (18). The mRNAs encoding normal cellular proteins persist in the cytoplasm; however, they are not translated during heat shock. When returned to normal temperatures, the synthesis of normal cellular proteins resumes even in the presence of actinomycin D, indicating that these mRNAs that had been quiescent during heat shock are reactivated during recovery (9).In yeast, the shift in gene expression is controlled at the transcriptional level. Heat shock induces the transcription of genes encoding hsps but represses the transcription of genes encoding normal cellular proteins. The normal cellular protein mRNAs already present in the cytoplasm continue to be translated (along with hsp mRNAs) until they are turned over at their normal, fairly rapid rates (13). In soybean a similar transcriptional regulation of normal cellular protein synthesis appears to be operating. Vierling and Key (20) have demonstrated that the mRNA for the small subunit of ribulose-1,5-phosphate carboxylase decreases during heat shock, presumably as it is turned over at its normal rate.We have previously investigated the heat-shock response in the cells of barley aleurone layers (2). a-Amylases are the principal enzymes synthesized and secreted by these ...

Heat Shock Inhibits Release of the Signal Recognition Particle from the Endoplasmic Reticulum in Barley Aleurone Layers

“…In response to heat shock the normally stable message for ␣-amylase is rapidly degraded (8). At 25°C the half-life of the ␣-amylase mRNA was estimated to be over 100 h (9), yet within 30 min at 40°C over 60% of it was degraded (10). The same phenomenon has been observed for the mRNA levels for the secreted proteins endochitinase and protease, whereas the mRNA levels of the nonsecreted proteins actin and tubulin were not affected by heat shock (10).…”

Fungal Elicitor-Induced Bean Proline-Rich Protein mRNA Down-Regulation Is Due to Destabilization That Is Transcription and Translation Dependent.

“…It is not known whether the other elicitor down-regulated mRNAs identified by cDNA cloning (Sauer et al, 1990) or in vitro translation (Cramer et ai., 1985;Dalkin et al, 1990) are also regulated by differential mRNA stability. The response of plants to heat shock has also been shown to involve transcriptional activation of the heat shock protein genes and selective destabilization of existing mRNAs (Belanger et ai., 1986;Nover, 1989;Brodl and Ho, 1991). Although actinomycin D pretreatment reduced the degradation of the PvPRPl mRNA in elicitor-treated cells, there was no detectable effect of actinomycin D on P-tubulin mRNA degradation in these cells.…”

“…In the aleurone layers of gibberellin A 3 -treated barley seeds, a-amylase mRNA has a half-life of greater than 100 hr. After heat shock treatment, the a-amylase mRNA halflife is reduced to less than 2 hr (Belanger et al, 1986;Brodl and Ho, 1991). Under conditions of iron starvation, the transferrin receptor mRNA in human cells is also very stable, with a half-life of ~30 hr.…”

“…In the presence of excess iron, the transferrin receptor mRNA in mammalian cells is destabilized (Casey et al, 1988;Müllner and Kühn, 1988). In gibberellin-treated barley aleurone tissues, heat shock destabilizes a-amylase mRNA (Belanger et al, 1986;Brodl and Ho, 1991). In soybean seedlings, the transcripts of the ribulose-1 Bbisphosphate carboxylase small subunit (rbcS) genes are less stable in light-grown plants than in their etiolated counterparts (Shirley and Meagher, 1990).…”

Reduced Levels of Chloroplast FtsH Protein in Tobacco Mosaic Virus–Infected Tobacco Leaves Accelerate the Hypersensitive Reaction

“…Actually, a low sensitivity of actin and GAPDH genes to actinomycin D or heat shock has been reported (Brodl and Ho, 1991;Blattner et al, 1999). Interestingly, actinomycin D is an inducer of apoptosis, a genetically determined cell suicide program, in animals (Devitt et al, 1999;Li et al, 1999).…”