Genome-Wide Identification of Differentially Expressed Genes Associated with the High Yielding of Oleoresin in Secondary Xylem of Masson Pine (Pinus massoniana Lamb) by Transcriptomic Analysis.

Qinghua Liu,Zhongping Feng,Zhichun Zhou,Yongcheng Wei,Danyu Shen,Shanping Hong,Björn Hamberger

doi:10.1371/journal.pone.0132624

Qinghua Liu, Zhongping Feng + Show 5 more

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https://doi.org/10.1371/journal.pone.0132624

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Abstract

Masson pine is an important timber and resource for oleoresin in South China. Increasing yield of oleoresin in stems can raise economic benefits and enhance the resistance to bark beetles. However, the genetic mechanisms for regulating the yield of oleoresin were still unknown. Here, high-throughput sequencing technology was used to investigate the transcriptome and compare the gene expression profiles of high and low oleoresin-yielding genotypes. A total of 40,690,540 reads were obtained and assembled into 137,499 transcripts from the secondary xylem tissues. We identified 84,842 candidate unigenes based on sequence annotation using various databases and 96 unigenes were candidates for terpenoid backbone biosynthesis in pine. By comparing the expression profiles of high and low oleoresin-yielding genotypes, 649 differentially expressed genes (DEGs) were identified. GO enrichment analysis of DEGs revealed that multiple pathways were related to high yield of oleoresin. Nine candidate genes were validated by QPCR analysis. Among them, the candidate genes encoding geranylgeranyl diphosphate synthase (GGPS) and (-)-alpha/beta-pinene synthase were up-regulated in the high oleoresin-yielding genotype, while tricyclene synthase revealed lower expression level, which was in good agreement with the GC/MS result. In addition, DEG encoding ABC transporters, pathogenesis-related proteins (PR5 and PR9), phosphomethylpyrimidine synthase, non-specific lipid-transfer protein-like protein and ethylene responsive transcription factors (ERFs) were also confirmed to be critical for the biosynthesis of oleoresin. The next-generation sequencing strategy used in this study has proven to be a powerful means for analyzing transcriptome variation related to the yield of oleoresin in masson pine. The candidate genes encoding GGPS, (-)-alpha/beta-pinene, tricyclene synthase, ABC transporters, non-specific lipid-transfer protein-like protein, phosphomethylpyrimidine synthase, ERFs and pathogen responses may play important roles in regulating the yield of oleoresin. These DEGs are worthy of special attention in future studies.

Highlights

Oleoresin, as a mixture of many terpenoids including turpentine and rosin, is stored in resin ducts or blisters in stems, roots, needles and cones of conifer trees [1]
In order to reveal the compositional properties of oleoresin, we performed gas chromatography-mass spectrometry (GC/MS) analysis for high and low oleoresin-yielding masson pines
The candidate genes associated with oleoresin biosynthesis and the expression profiles of high and low oleoresin-yielding genotypes were characterized by de novo assembly and differentially expressed genes (DEGs) analysis

Summary

Introduction

As a mixture of many terpenoids including turpentine (monoterpenes and sesquiterpenes) and rosin (diterpenes), is stored in resin ducts or blisters in stems, roots, needles and cones of conifer trees [1]. Terpenoids can be exploited as advanced liquid biofuels. Biofuels derived from terpenoids have similar properties as diesel and gasoline, and the density and hygroscopicity are amenable to mixing with fossil fuels [6]. Terpenoids play an important role in defense system of conifer trees. The resin ducts or blisters are severed and oleoresin is released after suffering abiotic or biotic stimuli such as mechanical wounding, insect attack and pathogen invasion. Other studies have found that the trees releasing a large amount of oleoresin upon wounding exhibit the strongest resistance to beetle attack in southern pines [9]

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