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. 2021 Jan 19;22(2):948. doi: 10.3390/ijms22020948

Figure 2.

Figure 2

Two systems involved in heat stress responses in plants. Heat stress triggers protective mechanisms collectively called heat stress responses (HSRs). Both HSR in the cytoplasm and unfolded protein responses (UPR) in the endoplasmic reticulum (ER) mitigate the damage from heat stress and protect plants from further stress. The UPR and HSR occur in different cellular compartments, but both responses are elicited by misfolded proteins that accumulate in the ER and cytoplasm, respectively. The HSP and UPR genes in plants are upregulated by the activation of stress-transducing transcription factors, such as bZIP60 (basic leucine zipper 60) in the UPR and HSFs in the HSR. IRE1, a key factor in the UPR, is a dual protein kinase and ribonuclease involved in the splicing of bZIP60 mRNA. HSR, heat stress response; UPR, unfolded protein response; ER, endoplasmic reticulum; bZIP60, basic leucine zipper 60; HSP, heat shock protein; HSF, heat shock transcription factor; HSP70, heat shock protein 70; BIP, binding immunoglobulin protein; and IRE1, inositol-requiring enzyme 1.