Isoquinoline alkaloid composition and expression of biosynthetic genes in mechanically wounded sacred lotus

Abstract

Isoquinoline alkaloids, a plant secondary metabolites present in many plant species including lotus (Nelumbo nucifera Gaertn.). Lotus leaf contains high amount of bioactive nuciferine and N-nornuciferine. A set of enzyme including NCS, 6OMT and CNMT and WRKY transcription factors (WRKY TFs) has been reported to have corresponding function in the biosynthesis isoquinoline alkaloids. Thus, we performed quantitative analysis on expression level of these corresponing genes and on nuciferine and N-nornuciferine content in lotus leaf using mechanical wounding method. Sequence analysis clearly showed that all the targeted genes possess the conserved region belongs to their protein families. The accumulation of compound correlated well with expression of NCS, CNMT and one WRKY TFs (NNU_24385) in the wounded leaf. Pattern of gene expression suggested that CNMT played a role in the biosynthetic pathway before 6OMT. In normal condition, 6OMT and NCS showed the highest transcript level in young and mature tissues of wild Thai lotus organs, respectively, while NNU_24385 was dominant WRKY TFs in all subjected organs. Interestingly, expression of CNMT in the wounded leaf showed a well relationship with compound accumulation unlike the normal leaf; this may suggest an important role of CNMT. To conclude, CNMT and WRKY TFs (NNU_24385) played a dominant role in response to mechanical wounding in lotus leaf. Moreover, Rosem Plenum contain high level of compounds. Thus, this group may be a good source for the development on BIA production in commercial lotus.