Figure legends
Figure 1. The molecular mechanisms of yeast underlying high temperature response and thermotolerance
(1) Under normal circumstances, Hsf1p is inhibited by binding to Hsp70 which the association is weak. In response to high temperature, Hsf1p is released by binding of Hsp70p with misfolded protein, which then phosphorylates and imported into the nucleus recruiting mediators (Head, Middle, Tail, and Kinase) to increase the amount of RNA Pol II occupied and reconstructing the chromatin distribution in the promoters. The mediator is a conserved transcriptional coactivation complex. Its component subunits of Med2p, Med3p, and Med15p can recruit on regulatory regions of prompter, which enables smooth expression of target genes involving heat shock protein (HSPs), protein homeostasis and trehalose synthesis. (2) The number of new ribosomal proteins (RPs) and rRNAs do not match, resulting in the orphan r-proteins aggregate. Hsf1p is activated by them, which then stimulate the expression of protein homeostasis genes. On the other hand, Ifh1p also activated by orphan r-proteins, which in turn inhibits the synthesis of ribosomal protein genes. (3) Ras-PKA pathway influence the activation of Msn2/3p by phosphorylate. Stress leads Msn2/3p dephosphorylated, and then enters the nucleus and activate the downstream regulated genes expression which have stress response elements (STREs)
Figure 2. Deleterious effects of ethanol and acetic acid on yeast cells and cellular adaptive response to stress
(1) Fps1p is the aquaglyceroporin channel which transports the acetic acid from extracellular to cytoplasm, and it can interact with regulatory proteins Rgc1p/Rgc2p. To cope with acetic acid stress, Fps1p is closed in response to increases in cellular acetic acid concentration. And other ATPase-dependent transporters (Pdr10, Pdr12, Pma1) seem to play an important role in maintaining intracellular concentration of CH3COOH-/H+homeostasis. (2) Hyperphosphorylated Mks1p binds to Bmh1/2p, inhibiting the Rtg3p and Rtg1p complexes translocate to nucleus and inhibits the retrograde signals transmission in normal conditions. When the strains exposure to acetic acid, Mitochondrial dysfunction leads to a decrease in ATP content. And, Mks1p and Rtg2p are combined to inhibit the Mks1-Bmh1/2p complex function of inhibiting the RTG pathway, resulting in the activated Rtg3p-Rtg1p complex entering the cell nucleus to regulate RTG-dependent nuclear genes expression such as IDH1, IDH12, DLD3, PYC1. (3) HAA1 is sensitive to intracellular acetic acid. After too much acetic acid dissociated in the cell to form acetate, it will be activated by dephosphorylation, thus avoiding anionic toxicity. (4) To deal with cell membrane destruction caused by ethanol, Ssk1p which is Cytoplasmic phosphorelay intermediate regulator is activated by overexpressing Ole1p, then sequentially activates Ssk2/22p and Pbs2p. Finally, HOG pathway is stimulated by Pbs2p in response to ethanol stress.
Figure 3. Functional reaction to oxidant and Toxic molecule stress signals
(1) The activation of Yap1p is dependent or not on ROS caused by oxidizing chemicals, it transits from cytoplasm to nucleus to stimulate the expression of oxidative stress responsive gene such as GSH, GSN, SOD2 and GLR1. And, Hyr1p or Ybp1p-Gpx3p complex can inhibit YAP1 output from nuclear. (2) The unfolded protein response (UPR) signaling pathway mainly contains two regulators, i.e., the Ire1p and Hac1p. The original Hac1p mRNA contains introns which will inhibit its transcription activity. Once Ire1p releases from upon ER stress, Hac1p introns is cut to stimulate the expression of UPR genes expression. (3) The glutathione (GSH) and thioredoxin (TRX) system be respectively regard as representative of the non-enzymatic antioxidant system and enzyme antioxidant system. The sulfydryl of GSH has reducing activity interact with oxidizing chemicals to form oxidized glutathione (GSSG). Using glutathione reductase and NADPH to restore GSSG to GSH. And, the thioredoxin system includes thioredoxin reductase, thioredoxin and thioredoxin peroxidase. Thioredoxin (TPX) is a class of thiol-rich proteins. It can be used as a reducing substrate to maintain intracellular redox together with thioredoxin reductase. (3) The glutathione (GSH) and thioredoxin (TRX) system be respectively regard as representative of the non-enzymatic antioxidant system and enzyme antioxidant system. The sulfydryl of GSH has reducing activity interact with oxidizing chemicals to form oxidized glutathione (GSSG). Using glutathione reductase and NADPH to restore GSSG to GSH. And, the thioredoxin system includes thioredoxin reductase, thioredoxin and thioredoxin peroxidase. Thioredoxin (TPX) is a class of thiol-rich proteins. It can be used as a reducing substrate to maintain intracellular redox together with thioredoxin reductase.
Figure 4. Transcription Factor Engineering used to improve strains industrial value and create new tools
(A) The conventional gene modifying methods including overexpression and knockout can be brought into reconstructing metabolic networks, especially in stress defense system. (B) gTME and heterologous expression based on multi-TF structures provides a possibility for promoting self-activity and enhancing gene transcription level that contribute to the tolerance and productivity. (C) ATF together with their cognate binding sites (CBS) and synthetic promoter (PSyn) construct an orthorhombic gene expression system to regulate the genes expression. (D) TF-based biosensors consist of effector domain (ED) for sensing small molecules and DNA-binding domain (DBD) combined with DNA, which provides more opportunities to quantitatively evaluating substance content.