De novo transcriptome sequencing, assembly and characterization of Heliopsis longipes roots vs. leaves to discover putative genes involved in specialized metabolites biosynthesis

Abstract

Heliopsis longipes is a valuable source of specialized metabolites (or secondary metabolites) with medicinal properties mainly in roots. However, little is known about genes involved in the biosynthesis of these metabolites, primarily due to the lack of genome or transcriptome resources. In this work, the genes of the biosynthetic pathway of the specialized metabolism from H. longipes roots and leaves through de novo RNA sequencing (RNA-Seq) using the platform of Illumina paired-end sequencing were studied. After de novo transcriptome assembly using the software Newbler, a total of 172,342 non-redundant transcripts with an N50 value of 816 bp was obtained. Further functional classification and annotation with Gene Ontology (GO), BLAST2GO, Kyoto Encyclopedia of Genes and Genome (KEGG), and KEGG automatic annotation server (KAAS), revealed that active genes in tissues are predominately involved in the metabolic process and biosynthesis of specialized metabolite pathways. Differential expression analysis of roots vs. leaves using Cuffdiff software (p-value ≤0.05 and log-fold change ratio (log2) ≥1) revealed that differentially expressed genes (DEGs) were in an organ-specific manner, such as in leaf, DEGs were significantly enriched in photosynthesis, while in roots, were a higher enriched function of plant hormone signal transduction. A total of 63 transcripts DEGs were related to 9 specialized metabolites pathways, in roots the most abundant was the phenylpropanoid biosynthesis, and in leaves was the carotenoids biosynthesis. Several regulatory genes including the basic-helix-loop-helix and basic leucine zipper domain, transcriptions factor families involved in the regulation of phenylpropanoids and carotenoid biosynthesis, respectively, were discovered. This study established a global transcriptome dataset for H. longipes. Data shall be useful to study the functional genomics or genetic engineering of this specie. These results will promote the understanding of the genetic mechanism involved in the biosynthesis of specialized metabolites in H. longipes