Abstract
Lonicera japonica is one of the most important medicinal plants with applications in traditional Chinese and Japanese medicine for thousands of years. Extensive studies on the constituents of L. japonica extracts have revealed an accumulation of pharmaceutically active metabolite classes, such as chlorogenic acid, luteolin and other flavonoids, and secoiridoids, which impart characteristic medicinal properties. Despite being a rich source of pharmaceutically active metabolites, little is known about the biosynthetic enzymes involved, and their expression profile across different tissues of L. japonica. In this study, we performed de novo transcriptome assembly for L. japonica, representing transcripts from nine different tissues. A total of 22 Gbps clean RNA-seq reads from nine tissues of L. japonica were used, resulting in 243,185 unigenes, with 99,938 unigenes annotated based on a homology search using blastx against the NCBI-nr protein database. Unsupervised principal component analysis and correlation studies using transcript expression data from all nine tissues of L. japonica showed relationships between tissues, explaining their association at different developmental stages. Homologs for all genes associated with chlorogenic acid, luteolin, and secoiridoid biosynthesis pathways were identified in the L. japonica transcriptome assembly. Expression of unigenes associated with chlorogenic acid was enriched in stems and leaf-2, unigenes from luteolin were enriched in stems and flowers, while unigenes from secoiridoid metabolic pathways were enriched in leaf-1 and shoot apex. Our results showed that different tissues of L. japonica are enriched with sets of unigenes associated with specific pharmaceutically important metabolic pathways and, therefore, possess unique medicinal properties. The present study will serve as a resource for future attempts for functional characterization of enzyme coding genes within key metabolic processes.
Highlights
Lonicera japonica Thunb, known as Japanese honeysuckle, ‘Jin Yin Hua’, and ‘Ren Dong’, belongs to the Caprifoliaceae family and is often used in traditional Chinese and Japanese medicine [1]
Our results showed that different tissues of L. japonica are enriched with sets of unigenes associated with specific pharmaceutically important metabolic pathways and, possess unique medicinal properties
Our principal component analysis (PCA) and correlation analysis for all nine tissues of L. japonica suggests the presence of signature unigenes associated with and specific to each tissue, and overlap of transcript expression across tissues was related to their association at different stages of development
Summary
Lonicera japonica Thunb, known as Japanese honeysuckle, ‘Jin Yin Hua’, and ‘Ren Dong’, belongs to the Caprifoliaceae family and is often used in traditional Chinese and Japanese medicine [1]. Different parts of L. japonica have been reported to possess unique medicinal properties, with flowers and floral buds being highly used in Chinese traditional medicine, while the leaves and stems are used in Japan [2, 4, 5]. Several studies on chemical constituents across different tissues have shown a higher content of CGA and luteolosides in floral buds, leaves and stems of L. japonica [1, 5, 7]. Previous transcriptome-based studies on L. japonica described transcripts across leaves and different floral developmental stages, and were focused on CGA, luteolosides, and flavonoid biosynthesis [2, 6]. Genes involved in secoiridoid metabolic pathways, one of the major chemical constituents with important pharmaceutical properties, have not been studied in L. japonica. This study presents a comprehensive transcriptome profiling and analysis for L. japonica, and will be useful as a resource for future functional characterization of enzymes of interest
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