# Trepenes and Trepenoids in Plants: Interactions with Environment and Insects
## 1 Plant Trepenes in Abiotic Stress
### Stress Response and Terpenoid Biosynthetic Genes
Mechano-sensitive channels through the CWI pathway may also play a role in sensing cellular stress and initiating a signal transduction cascade. ROS during stress is generated at various hotspots, particularly in metabolically active organelles, i.e., chloroplast, mitochondria, peroxisomes, and the endoplasmic reticulum. When ROS production exceeds the quenching capacity of the cell or cellular organelles, retrograde signaling is initiated either through ROS or through ROS-activated/dependent signaling pathways. ROS signals from different organelles may be integrated and fine-tuned through the ER-MCS. To prevent  
photoinhibition in the chloroplast, particularly that of PSII, CEE, Mehler peroxidase reaction, and photorespiration may relieve the system of the excess of reducing equivalents, while antioxidant defense systems such as the ascorbate-glutathione cycle may alleviate oxidative stress by quenching ROS. PS/II, photosystem I/II; Ph, pheoplytrium; PO, plastoquinone; Cytbef, cytochrome b6/t complex; FD, ferredoxin; FNR; ferredoxin NADP* reductase; CEE, cyclic electron flow; RuBP, ribulose-1,5-bipphosphate; RuBiSCO, ribulose-1,5-bipphosphate carboxylase; SOX, superoxide dismutase; Asc, ascorbic: MDA, monodeby-droscarbate; AP, ascorbate peroxidase; MDAR, mendohydrocoscarbate reductase; DHA, dehydroroscarbate reductase; DHA, dehydroroscarbate; CSSG, oxidized glutathione; GSH, reduced glutathione; GR, glutathione reductase; DHAR, dehydroroscarbate reductase; SAA, systemic acquired acclimation; CWI, cell-wall integrity; GPCR, G-protein-coupled receptors; PLC, phospholipase C; PIP, phosphatidylinositol-1,5-bipphosphate; DAG, diacylglycerolglycerol; PKC, protein kinase C; InsP3, inositol-1,4,5-triphosphate; CPK, calcium-dependent protein kinase; CBI, calcineurin B-like; CIFK, CBI-interacting protein kinase; SOS, salt overly sensitive; SnRK, SNFI/AMPK-related kinase; ABA, abscisic acid; Rbomb/D; respiratory burst oxidase homolog; D/F, Tris transcription factors; ER, endoplasmic reticulum; ER-MSC, ER-membrane contact sites; UPR, unfolded protein response; OPF, oxidative protein folding; MEP2-cmethyl-D-erythbridt-d-phosphate; MVA, mexulic acid; G3P, glyceraldehyde-3-phosphate; DS, 1-deoxy-D-xylulose-5-phosphate synthase; DXP, 1-deoxy-D-xylulose-5-phosphate; DXR, 1-deoxy-D-xylulose-5-phosphate reductase; MCT, 2-C-methyl-d-erythbridt-4-phosphate cytidyltransferase; CD-ME, 4-(cytidine-5'-diphospho)-2-C-methyl-D-erythbridt; CMK, 4-diphosphocytidyl-2-C-methyl-D-erythbridt kinase, CD-ME2P, 4-(cytidine-5'-diphospho)-2-C-methyl-D-erythbridt-2-phosphate; MDS, 2-C-methyl-d-erythbridt-2,4-cyclodiphosphate synthase: ME-CP, methylerythbridt cyclodiphosphate; HDS, 4-hydroxy-3-methyl-but-2-enyl-diphosphate synthase: PEP, phosphoenolpyruvate; AACT, acetyl-CoA acetyltransferase; HMGS, HMG-CoA synthase; HMGC-CoA reductase; MVA, mexulonate/mycalonic acid; MK, mexulonate kinase; MYP, mexulonate-5-phosphate; PMK, phosphoenvalonate kinase; MVPP, mexulonate pyrophosphate; MVD, diphosphopaneolonate decarboxylase; IPP, isopenval; DYrophosphate; DMAPP, dimethylallyl pyrophosphate; IDI, IPP-DMAPP isomerase; PT, premyl transferase; GPP, geranyl pyrophosphate; FFP, farnesyl pyrophosphate; GGPP, geranylgeranyl pyrophosphate. Photosynthetic REDOX signals and quenching are an adaptation of [27], while the terpenoid biosynthesis pathway is directly adopted from [28; 29]Figure 2: Phylogenetic classification of terpene synthases (TPSs) based on PFAM PF01397 and PF03936 SEED alignments reconstructed using PhyML 3.0 maximum likelihood method [30, 31]. Automatic model selection was based on Smart Model Selection (SMS) in PhyML [32], while the aLRT SH-like algorithm was used in place of bootstrap analysis. TPS protein sequences were classified into subfamilies using Terzyme [33]. The resulting phylogenetic trees were visualized using Evolview v3 [34]. PFAM Accession numbers/IDs are indicated at the leaf nodes, with corresponding background colors representing \(TPS\) gene subfamily affiliations. Bars (0.1 and 1) indicate mean amino acid substitution per site.