LtMYB305 transcription factor regulates the expression of LtLCYB gene to mediate carotenoids synthesis in Liriodendron petals

Carotenoids are a group of naturally occurring tetraterpenoid with great industrial and pharmacological value. The carotenoids biosynthesis was extensively elucidated in model plants, such as tomato and monkey flower. However, little is known about the regulation mechanism of carotenoids biosynthesis. Here, we used L. chinense and L. tulipifera petals as materials to study the differences in carotenoid accumulation. We seek to unveil the mystery via morphologic, metabolomic, transcriptomic, bioinformatics and transgenic approaches. The paraffin section of petals showed that cell morphology was almost the same in Liriodendron genus, while the quantification of carotenoids content displayed a different pattern in petals between two Liriodendron species, with high concentrations of carotenoids accumulated on the orange band (OB) in L. tulipifera petals. Correspondingly, KEGG analysis showed that carotenoids biosynthesis pathway was significantly enriched in L. tulipifera. HPLC and transcriptome analyses indicated that LtLCYB might be a key gene functioning in OB coloration, thus further characterization was conducted. RT-qPCR and subcellular localization showed that LtLCYB was highly expressed in OB, and the LtLCYB was a chloroplast-located protein. Overexpression of LtLCYB in tobacco promoted the carotenoid synthesis. Furthermore, we identified R2R3-MYB TFs and found a potential member that maybe related to OB coloration. Y1H assay proved that LtMYB305 bind to LCYB promoter. Overexpression of LtMYB305 in tobacco increased the carotenoid content. Collectively, our findings proposed that the OB coloration in Liriodendron stems from the interspecies variation in the differential expression of CBP genes, and LtMYB305 takes a pivotal role in OB coloration. This study establishes a robust foundation for investigating the regulation mechanism of carotenoid synthesis, and offers valuable insights for the genetic improvement of petal colors in Liriodendron.