Genetic variance and transcriptional regulation modulate terpenoid biosynthesis in trichomes of Nicotiana tabacum under drought

Abstract Drought affects aromatic terpenoids biosynthesis in plant, but the associated regulatory mechanism is unknown. We investigated large-scale dynamic changes in trichomes, terpenoids, and transcriptomes in leaves of Nicotiana tabacum varieties K326 and Basma Xanthi with three replicates over five time-courses with or without drought treatment. We found drought affects trichome type, trichome density, and abundance of major terpenoids examined by gas chromatography-mass spectrometry analysis. Further RNA-Seq analysis revealed drought induced common and variety-specific expressional regulation on differentially expressed genes in terpenoid backbone and diterpenoid biosynthesis, including cembratrien-ol synthase gene, cytochrome P450 gene CYP71D16, and copalyl diphosphate synthase (CPS) gene. The correlation between these genes’ expression and terpenoid abundance is positive under well-watered conditions but is variety specific under drought. A single mutation G to T, instead of two co-existed known mutations, in CPS exon 4 was identified in K326 where labdenediols were absent. Further full-length transcript comparison revealed splicing regulation in transcript CPS in both varieties. A truncated 3′-end splicing of CPS transcripts may also contribute to the absence of labdenediols in K326. Thus, our results provide further understanding of the regulatory mechanism of diterpenoid biosynthesis under drought stress, which may guide crop breeding and farming.