Seasonal Variation in Transcriptomic Profiling of Tetrastigma hemsleyanum Fully Developed Tuberous Roots Enriches Candidate Genes in Essential Metabolic Pathways and Phytohormone Signaling.

Qianqian Xiang,Ayalew Ligaba-Osena,Fudan Tong,Siyuan Hu,Jiayao Yang,Wanli Guo

doi:10.3389/fpls.2021.659645

Abstract

Tetrastigma hemsleyanum Diels et Gilg (Sanyeqing, SYQ) is a perennial climbing liana and an endemic plant to southern China. Its tuberous roots (TRs) are used in traditional Chinese medicine for treating some diseases such as high fever, pneumonia, asthma, hepatitis, and cancers. However, the mechanisms underlying the development of TR and the content of flavonoids and phenylpropanoids (FPs) are not well-understood. In this study, we performed a transcriptomic analysis of 12 fully developed TR (FD-TR) samples harvested in four seasons [spring (Sp), summer (Su), autumn (Au), and winter (Wi)] using the RNA-Sequencing (RNA-Seq). We obtained a total of 78.54 Gb raw data and 65,578 unigenes. Then, the unigenes were annotated by using six databases such as non-redundant protein database (NR), Pfam, eggNOG, SWISSProt, Kyoto Encyclopedia of Genes and Genomes (KEGG), and gene ontology (GO). The transcriptomic profiling showed closer relationships between the samples obtained in Su and Au than those obtained in Sp and Wi based on the results of both total unigenes and differentially expressed genes (DEGs). Three pathways, including the biosynthesis of FPs, metabolism of starch and sucrose, and signaling of phytohormones, were highly enriched, suggesting a gene-level seasonal variation. Based on the numbers of DEGs, brassinosteroid (BR) signal transduction factors appeared to play a key role in modulating the development of TRs while most of the auxin signaling genes were mainly activated in Wi and Sp FD-TRs. Most genes in the biosynthesis and biodegradation of starch and biodegradation of cellulose were activated in Wi FD-TRs. As determined by the high performance liquid chromatography (HPLC) and aluminum nitrate colorimetric method, the contents of total flavonoids and most detected FP components increased from Sp to Au but decreased in Wi. Enhanced expression levels of some genes in the biosynthetic pathways of FPs were detected in Su and Au samples, which corroborated well with metabolite content. Our findings provide the first transcriptomic and biochemical data on a seasonal variation in the composition of medically important metabolites in SYQ FD-TRs.

Highlights

Tetrastigma hemsleyanum Diels et Gilg (Sanyeqing, Tetrastigma hemsleyanum Diels et Gilg or Sanyeqing (SYQ)) is a perennial plant species belonging to the Vitaceae family
To study the transcriptomic changes between fully developed tuberous root (TR) (FD-TR) of T. hemsleyanum harvested in the four seasons (Sp, Su, Au, and Wi), complementary DNA (cDNA) libraries were generated from the three biological replicates and sequenced by using the Illumina Hiseq 4000
The levels of these metabolites and expression of some genes in their biosynthesis pathways were higher in Au or Su, suggesting that Au is the best season for harvesting TR, and we detected some genes in the flavonoids and phenylpropanoids (FPs) biosynthesis that were induced significantly in Au, suggesting a role in FP biosynthetic pathways

Summary

Introduction

Tetrastigma hemsleyanum Diels et Gilg (Sanyeqing, SYQ) is a perennial plant species belonging to the Vitaceae family. It is a diploid species (2n = 52) with climbing liana forming tuberous roots (TRs) during its lifecycle. SYQ is endemic to subtropical China, including Zhejiang, Fujian, Jiangxi, Yunnan, Guangxi, and Guangdong provinces H. et al, 2015; Guo et al, 2019), and is not resistant to low temperature (Peng et al, 2019). SYQ TRs are rich in phenylpropanoids, flavonoids, and polysaccharides (Guo et al, 2019; Zhu et al, 2020).

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