Transcriptomic comparison of Tylophora indica and Tylophora pauciflora leaves indicates major contribution of the ornithine pathway in tylophorine accumulation
摘要
Transcriptomic comparison of tylophorine-containing Tylophora indica and tylophorine-deficient Tylophora pauciflora leaves identified a differentially expressed TiNAOD, which was characterized through VIGS for its role in tylophorine accumulation in T. indica.
AbstractOrnithine, tyrosine, and phenylalanine are considered to be biogenetic precursors for phenanthroindolizidine alkaloids (PIAs), but their relative contribution to the metabolic flux is not clear. Tylophorine is a major PIA of Tylophora indica, whereas another closely related species, T. pauciflora, is deficient in tylophorine. Here, transcriptomic comparison of leaves of both the species was carried out to explore the role of differential gene expression in species diversity. Differentially expressed genes (DEGs) between the two species were identified with the help of a master transcriptome assembled using combined data from both the species. Many DEGs could be related to the discernible differences between the two species. Notably, N-acetylornithine deacetylase (NAOD) was found to be downregulated in T. pauciflora compared to T. indica. Molecular cloning of TiNAOD was carried out and its VIGS in T. indica resulted in reduced levels of ornithine and tylophorine. The major role of ornithine in biosynthesis of key PIA, tylophorine, was also corroborated by feeding T. indica leaves with tyrosine, phenylalanine, and ornithine, whereby the impact of ornithine was maximal in terms of tylophorine accumulation. This cross-species study has provided insights into gene expression-dependent Tylophora species diversity and also elucidated the major contribution of ornithine in tylophorine biosynthesis.
Graphical abstract