N⁶-methyladenosine RNA modification regulates light intensity-dependent terpenoid biosynthesis in Schizonepeta...

Schizonepeta tenuifolia Briq. (S. tenuifolia) is a traditional Chinese medicinal plant widely used to treat colds, fever and respiratory diseases. Volatile oils including the monoterpenoids limonene, pulegone and menthone are major constituents of S. tenuifolia that determine its medicinal value and consumer popularity. A better understanding of the molecular regulatory mechanisms underlying terpenoid accumulation is needed to improve the quality and market value of S. tenuifolia. Here, we demonstrate that limonene and pulegone accumulate in S. tenuifolia under high-light conditions, whereas menthone accumulates in the dark. Transcriptome and proteome analyses revealed that light up-regulated both the transcriptional and protein levels of limonene synthase (LS), whereas darkness elevated pulegone reductase (PR) expression and protein abundance. An N⁶-methyladenosine (m⁶A) dot blot assay revealed that levels of m⁶A modification are higher in the dark than in the light. Silencing of individual m⁶A writer genes resulted in higher levels of monoterpenoids such as menthone, pulegone and limonene in S. tenuifolia. We further determined that m⁶A modulates the content of monoterpenoids in S. tenuifolia by affecting the stability of transcripts encoding PR and LS. This study reveals a vital role for post-transcriptional regulation mediated by the m⁶A modification in light intensity-dependent terpenoid biosynthesis in S. tenuifolia and provides a strategy for genetically improving the quality of this valuable plant.