Identification, expression, and phylogenetic analyses of terpenoid biosynthesis-related genes in secondary xylem of loblolly pine (Pinus taeda L.) based on transcriptome analyses

Jipeng Mao,Tianyi Liu,Shaowei Huang,Zidi He,Jiehu Chen,Jing Hao

doi:10.7717/peerj.6124

Abstract

Loblolly pine (Pinus taeda L.) is one of the most important species for oleoresin (a mixture of terpenoids) in South China. The high oleoresin content of loblolly pine is associated with resistance to bark beetles and other economic benefits. In this study, we conducted transcriptome analyses of loblolly pine secondary xylem to gain insight into the genes involved in terpenoid biosynthesis. A total of 372 unigenes were identified as being critical for oleoresin production, including genes for ATP-binding cassette (ABC) transporters, the cytochrome P450 (CYP) protein family, and terpenoid backbone biosynthesis enzymes. Six key genes involved in terpenoid biosynthetic pathways were selected for multiple sequence alignment, conserved motif prediction, and phylogenetic and expression profile analyses. The protein sequences of all six genes exhibited a higher degree of sequence conservation, and upstream genes were relatively more conserved than downstream genes in terpenoid biosynthetic pathways. The N-terminal regions of these sequences were less conserved than the C-terminal ends, as the N-terminals were quite diverse in both length and composition. The phylogenetic analyses revealed that most genes originated from gene duplication after species divergence, and partial genes exhibited incomplete lineage sorting. In addition, the expression profile analyses showed that all six genes exhibited high expression levels during the high-oleoresin-yielding phase.

Highlights

The loblolly pine’s amenability to plantation management, high wood yields, and fast growth make it one of the most economically important forest species in the world (Lu et al, 2017)
To obtaine a summarization of the loblolly pine transcriptome in secondary xylem tissues during the high-oleoresin-yielding phase (August), total RNAs extracted from three samples were used for RNA-Seq on an Illumina HiSeq 4,000 platform
31,370 (42.16%), 30,395 (40.85%), 27,942 (37.56%), 24,871 (33.43%), and 22,433 (30.15%) unigenes were annotated by the UniProt, Nr, Kyoto Encyclopedia of Genes and Genomes (KEGG), KOG, and Gene Ontology (GO) databases, respectively (Table 1, Fig. 3)

Summary

Introduction

The loblolly pine’s amenability to plantation management, high wood yields, and fast growth make it one of the most economically important forest species in the world (Lu et al, 2017). Identification, expression, and phylogenetic analyses of terpenoid biosynthesis-related genes in secondary xylem of loblolly pine (Pinus taeda L.) based on transcriptome analyses. The resin canals distributed in secondary vascular structures can be divided into transverse and vertical resin canals. In the secondary xylem in particular, the transverse and vertical resin canals form a two-dimensional network structure; this two-dimensional resin canal structure allows the pine plant to effectively secrete resin at any point of invasion when subjected to biotic stresses (Chen & Yuan, 2002). Partial volatile terpenoids are inducible upon insect herbivory, oviposition, or fungal inoculation. These relationships are ancient and complex (Scott, Anderson & Anderson, 2004)

Methods

Results

Discussion

Conclusion