Abstract
Diterpene resin acids (DRAs) are major components of pine oleoresin that can effectively resist the invasion of insects and pathogenic microorganisms. The subfamily of cytochrome P450s, CYP720B, catalyzes diterpene products into DRAs. Identifying CYP720B subfamily members and revealing the characteristics of tissue-specific expression would help understand diterpene-rich structures and diverse types. Slash pine and loblolly pine are important pines that provide oleoresin products. In this study, we identified CYP720B candidate genes based on the Pinus taeda V2.0 genome and full-length transcriptome of slash pine by PacBio. A total of 17 genes in slash pine and 19 in loblolly pine were identified and classified into four main clades by phylogenetic analysis. An analysis of cis-acting elements showed that CYP720B genes were closely related to adversity resistance. The gene expression of these candidates in different tissues was quantified by real-time quantitative PCR (RT–qPCR) analysis. Most of the genes showed relatively higher expression levels in roots and stems than in the other tissues, corresponding with the results of DRA component detection by gas chromatography–mass spectrometry (GC–MS), which indicated that stems and roots might be important tissues in oleoresin biosynthesis. These results provide a valuable resource for a better understanding of the biological role of individual CYP720Bs in slash pine and loblolly pine.
Highlights
Based on the presence of apparently complete P450 enzymes (P450s) domains, 17 CYP720B candidate genes were identified in slash pine and 19 were identified in loblolly pine
We found that the Diterpene resin acids (DRAs) profile detected by gas chromatography–mass spectrometry (GC–MS) was quite different among tissues, which was consistent with previous studies [5,38]
This study conducted an analysis of CYP720B genes in slash pine and loblolly pine
Summary
DRAs, which are major components of pine oleoresin, play a critical role in conifer defense against insects and pathogens [5]. DRAs, originating from a common acyclic biosynthetic precursor (geranylgeranyl diphosphate, GGPP), are composed of 20-carbon bi- or tricyclic carboxylic acids of carbon skeletal types, commonly catalyzed by terpene synthases (TPSs) and cytochrome P450 enzymes (P450s) [6]. Their biosynthesis involves two steps: (1) diTPS catalyzes GGPP for multistep cyclization and rearrangement to produce various bicyclic or tricyclic diterpenes; (2) carbon-18 in diterpenes is oxidized three times by P450s to form corresponding DRAs [7,8]. Diterpene synthase causes the structural diversity of the diterpene backbone, and P450s catalyze various oxidation and hydroxylation reactions in the primary and secondary metabolic processes of plants to produce various defensive
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