A Model of HSP70 Synthesis in Barley Aleurone Cells During Heat Shock

Heat shock is a naturally occurring environmental stressor for plants. This stressor usually causes protein dysfunction and prevents them from properly folding, assembling, translocating and degrading. Heat-shock proteins (Hsps)/chaperones are a response protein that helps in providing assistance against the protein dysfunctions listed above. They play a critical role in protecting plants from the stress of heat-shock. They do this by re-establishing homeostasis within the cell, by either stabilizing existing structures (role of small Hsps) or allowing proteins to refold (the large Hsps). Thus, there are several different classes of heat shock proteins that help in stabilizing the cell. The one that we will be focusing on, however, is Hsp70. This Hsp interacts with a variety of cochaperone proteins that help in refolding the unfolded proteins (Wang et al., 2004). The major role that Hsp70 plays in cells are preventing aggregation, assisting refolding, protein import and translocation, signal transduction, and transcriptional activation (Wang et al., 2004). It is additionally one of the first Hsps to be expressed during HSR. On top of this, some Hsp70 help to control the folded regulatory proteins, and may actually act as a negative repressor of heat-shock factor (HSF) mediated transcription (Wang et al., 2004). In our particular study, we are looking at the secretion of alpha-amylase mRNA and the synthesis of Hsp70 proteins as a result of heat-shock that takes place in the aleurone layer of barley. To test whether or not these Hsps assist in the destabilized alpha-amylase mRNA or of the delamellation process of the Endoplasmic Reticulum (ER), heat shocked cells were treated with the transcription inhibitor cordycepin, which effectively inhibits the synthesis of hsps yet does not affect alpha-amylase synthesis after this enzyme has been fully induced by gibberellic acid (12 hours) (Brodl et al., 1990). Although Hsps have been known to help with thermotolerance, in barley aleurone cells they do not play a major role in other heat-shock induced changes their targets are primarily existing proteins, and so Hsp70 does not confer thermo-protection to larger structures such as the endoplasmic reticulum (Brodl et al., 1990). In this paper, we explore the extant literature to help inform and contextualize our modeling project on Hsp70 and its effects in the aleurone layer in barley. We have constructed a system of differential equations designed to model