Advances in the Biosynthesis of Terpenoids and Their Ecological Functions in Plant Resistance

Abstract

Secondary metabolism plays an important role in the adaptation of plants to their environments, particularly by mediating bio-interactions and protecting plants from herbivores, insects, and pathogens. Terpenoids form the largest group of plant secondary metabolites, and their biosynthesis and regulation are extremely complicated. Terpenoids are key players in the interactions and defense reactions between plants, microorganisms, and animals. Terpene compounds are of great significance both to plants themselves and the ecological environment. On the one hand, while protecting plants themselves, they can also have an impact on the environment, thereby affecting the evolution of plant communities and even ecosystems. On the other hand, their economic value is gradually becoming clear in various aspects of human life; their potential is enormous, and they have broad application prospects. Therefore, research on terpenoids is crucial for plants, especially crops. This review paper is mainly focused on the following six aspects: plant terpenes (especially terpene volatiles and plant defense); their ecological functions; their biosynthesis and transport; related synthesis genes and their regulation; terpene homologues; and research and application prospects. We will provide readers with a systematic introduction to terpenoids covering the above aspects.

Keywords: disease; insects; interaction; plant resistance; terpenoids.

Figure 1

The functions of plant terpenoids and terpene homologues. Terpenoids and terpene homologues play important roles in plants by regulating resistance to biotic stress (including insect and disease resistance). Terpenoids also have many significant impacts on human life, and they can play a role in anti-inflammatory, antioxidant, anti-aggregation, anticoagulant, anti-tumor, sedative, and analgesic activities. Artemisinin is one such example.

Figure 2

Sketch map of biosynthesis of terpenoids and terpene homologues in plants: the MVA pathway in the cytoplasm and the MEP pathway in plastids. Abbreviations: AACT, acetoacetyl-CoA thiolase; AcAc-CoA, acetoacetyl-CoA; HMGS, HMG-CoA synthase; HMG-CoA, 3-hydroxy-3-methylglutaryl-Coenzyme A; HMGR, HMG-CoA reductase; MVA, mevalonic acid; MK, mevalonate kinase; MVAP, mevalonate 5-phosphate; PMK, phosphomevalonate kinase; MVAPP, mevalonate 5-diphosphate; MDD, mevalonate diphosphate decarboxylase; IPP, isopentenyl diphosphate; IPPI, IPP isomerase; DMAPP, dimethylallyl diphosphate; G3P, glyceraldehyde-3-phosphate; DXS, 1-deoxy-D-xylulose-5-phosphate synthase; DXP, 1-deoxy-D-xylulose-5-phosphate; DXR, 1-deoxy-D-xylulose-5-phosphate reductoisomerase; MEP, 2-C-methylerythritol 4-phosphate; MCT, 2-C-methyl-D-erythritol 4-phosphate cytidylyltransferase; CDP-ME, 4-(cytidine 5’-diphospho)-2-C-methylD-erythritol; CMK, CDP-ME kinase; CDP-ME2P, 4-(cytidine 5’-diphospho)-2-C-methyl-D-erythritol phosphate; MDS, 2-C-methyl-D-erythritol 2,4-cyclodiphosphate synthase; MEcPP, 2-C-methyl-D-erythritol 2,4-cyclodiphosphate; HDS, (E)-4-hydroxy-3-methylbut-2-enyl diphosphate synthase; HMBPP, (E)-4-hydroxy-3-methylbut-2-enyl diphosphate; HDR, (E)-4-hydroxy-3-methylbut-2-enyl diphosphate reductase; GGPPS, geranyl Mapp diphosphate synthase; FPPS, farnesyl diphosphate synthase; GPS, GPP synthase; GGPP, geranylgeranyl diphosphate; FPP, farnesyl pyrophosphate; GPP, geranylvdiphosphate; mTPS, monoterpenoid synthase; sTPS, sesquiterpene synthase; dTPS, diterpene synthases; NES, nerolidol synthase; GLS, geranyllinalool synthase; SQS, squalene synthase; PSY, Phytoene synthase; DMNT, 4,8-dimethylnona-1,3,7-triene; TMTT, 4,8,12-trimethyltrideca-1,3,7,11-tetraene.