Deciphering the Complexity of Terpenoid Biosynthesis and Its Multi-level Regulatory Mechanism in Plants

Terpenoids are one of the essential plant metabolites which are known to play vital roles in plants' primary growth and development including protection from biotic and abiotic stresses. They have huge structural diversity and are known to provide various health benefits, flavors, fragrances, essential oils, cosmetics, pigments, insecticides, etc. The biosynthesis of terpenoids by mevalonic acid (MVA) and methylerythritol pathway (MEP) occurs inside the cytoplasm and the chloroplast, respectively. Here, we provide a comprehensive overview of synthesis, metabolic, and regulatory pathways of terpenoid, their different classes and ecological roles. We also discuss in detail the key transcription factors (TFs) like WRKY, AP2/ERF, bHLH, MYB, NAC, and bZIP which reprogram and modulate the terpenoid pathway in plants. It also includes the post-transcriptional and post-translational modifications of these pathways. The post-transcriptional regulation by microRNA plays a critical role in the synthesis and regulation of the terpenoid. MAP kinases also regulate the stability of biosynthetic enzymes and transcription factors to regulate terpenoid biosynthesis. High-throughput sequencing technology and functional genomics have further strengthened our understanding of this pathway and associated regulatory genes which control it. As a future perspective, modifying these transcription factors via various strategies holds promise for improvement of agricultural crop plants in terms of nutritional enrichment, stress responsiveness, and resistance.