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Solanesol, which mainly accumulates in solanaceous crops, including tobacco, tomato, potato, eggplant, and pepper plants, is a long-chain polyisoprenoid alcohol compound with nine isoprene units. Chemical synthesis of solanesol is difficult; therefore, solanesol is primarily extracted from solanaceous crops, particularly tobacco leaves. In plants, solanesol exists in both free and esterified forms, and its accumulation is influenced by genetic and environmental factors. Solanesol is widely used in the pharmaceutical industry as an intermediate for the synthesis of ubiquinone drugs, such as coenzyme Q10 and vitamin K2. Solanesol possesses antibacterial, antifungal, antiviral, anticancer, anti-inflammatory, and anti-ulcer activities, and solanesol derivatives also have anti-oxidant and antitumour activities, in addition to other bioactivities. Solanesol derivatives can also be used for the treatment of cardiovascular disease, osteoporosis, acquired immune deficiency syndrome, and wound healing. Solanesol biosynthesis occurs in plastids of higher plants via the 2-C-methyl-D-erythritol-4-phosphate (MEP) pathway. The key enzymes in solanesol biosynthesis, including 1-deoxy-D-xylulose-5-phosphate synthase, 1-deoxy-D-xylulose-5-phosphate-reductoisomerase, isopentenyl pyrophosphate isomerase, and solanesyl diphosphate synthase, are also important regulators of the MEP pathway, and their overexpression is favourable for downstream metabolic flow, further promoting the synthesis of downstream metabolites, such as solanesol. Future studies should determine the pharmacokinetic properties of solanesol and its derivatives and investigate the metabolic pathways and regulatory mechanisms mediating solanesol biosynthesis, metabolic and genetic engineering of solanesol, the synthetic biology of solanesol, and the physiological role of solanesol. In the present review, we systematically summarise current knowledge on solanesol resources, derivatives, bioactivities and medicinal applications, metabolic pathways, and key biosynthetic enzymes.

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Autotoxicity, defined as a deleterious allelopathic effect among individuals of the same plant species, is considered as one of the factors that contributes to replant failure. Tobacco, as an important cultured and economic crop over the world, has been often hampered by replant failure. In view of the seriousness of this problem, the allelochemicals of flue-cured tobacco and their allelopathic effects were investigated. The extracts of rhizosphere soil exhibited phytotoxic activities against Lactuca sativa and autotoxic activities against tobacco itself. Bioassay-guided fractionation of the extract led to the isolation of six compounds, the structures of which were elucidated by spectroscopic analysis. Among them, β-cembrenediol (1), di-n-hexyl phthalate (2), and bis(2-propylheptyl) phthalate (3) showed observably phytotoxic activities against L. sativa seedlings and autotoxic activities on tobacco. The allelochemicals were then verified in the root zone soils of flue-cured tobacco by high-performance liquid chromatography (HPLC). These results provide new insights into the allelopathic mechanisms involved in the replant failure of flue-cured tobacco.