Identification of genes related to agarwood formation: transcriptome analysis of healthy and wounded tissues of Aquilaria sinensis

Abstract

BackgroundAgarwood is an expensive resinous heartwood derived from Aquilaria plants that is widely used in traditional medicines, incense and perfume. Only wounded trees can produce agarwood, and the huge demand for the agarwood products has led all Aquilaria spp. being endangered and listed in the Appendix II of the CITES (http://www.cites.org). The major components of agarwood are sesquiterpenes and phenylethyl chromones. Owing to a lack of genomic information, the molecular basis of wound-induced sesquiterpenes biosynthesis and agarwood formation remains unknown.ResultsTo identify the primary genes that maybe related to agarwood formation, we sequenced 2 cDNA libraries generated from healthy and wounded A. sinensis (Lour.) Gilg. A total of 89,137 unigenes with an average length of 678.65 bp were obtained, and they were annotated in detail at bioinformatics levels. Of those associated with agarwood formation, 30 putatively encoded enzymes in the sesquiterpene biosynthesis pathway, and a handful of transcription factors and protein kinases were related to wound signal transduction. Three full-length cDNAs of sesquiterpene synthases (ASS1-3) were cloned and expressed in Escherichia coli, and enzyme assays revealed that they are active enzymes, with the major products being δ-guaiene. A methyl jasmonate (MJ) induction experiment revealed that the expression of ASS was significantly induced by MJ, and the production of sesquiterpenes was elevated accordingly. The expression of some transcription factors and protein kinases, especially MYB4, WRKY4, MPKK2 and MAPK2, was also induced by MJ and coordinated with ASS expression, suggesting they maybe positive regulators of ASS.ConclusionsThis study provides extensive transcriptome information for Aquilaria spp. and valuable clues for elucidating the mechanism of wound-induced agarwood sesquiterpenes biosynthesis and their regulation.

Defense Responses in Aspen with Altered Pectin Methylesterase Activity Reveal the Hormonal Inducers of Tyloses

“…Tyloses are typically induced to form in the embolized vessels by wounding, pathogen attack, and preceding the heartwood formation (Biggs, 1987;Schmitt and Liese, 1993;Taylor et al, 2002;Sun et al, 2006Sun et al, , 2008Pérez-Donoso et al, 2007;Collins et al, 2009), which are the physiological processes in which jasmonates have been implicated (Wasternack and Hause, 2013;Huang et al, 2013;Xu et al, 2013), but no direct involvement of jasmonates in tyloses formation has yet been demonstrated. This study provides the evidence that jasmonates are capable of inducing tyloses and their accompanying gels in plants.…”

“…ET concentration was also observed to increase in the transition zone where the heartwood is being formed (Taylor et al, 2002) and during infections (Pérez-Donoso et al, 2007;McElrone et al, 2010); that is, under circumstances in which tyloses are induced. Recent transcriptomics studies of heartwood formation indicated up-regulation of ET and other stress signaling pathways during this process (Huang et al, 2013;Xu et al, 2013). Moreover, the formation of agarwood, which is the commercially valuable heartwood of Aquilaria sinensis, was intensified by applying methyl jasmonate (MeJA) to the cut stems (Xu et al, 2013), implying the involvement of jasmonates in heartwood induction.…”

“…Recent transcriptomics studies of heartwood formation indicated up-regulation of ET and other stress signaling pathways during this process (Huang et al, 2013;Xu et al, 2013). Moreover, the formation of agarwood, which is the commercially valuable heartwood of Aquilaria sinensis, was intensified by applying methyl jasmonate (MeJA) to the cut stems (Xu et al, 2013), implying the involvement of jasmonates in heartwood induction. However, the induction of tyloses by any of these hormones in intact healthy plants has not previously been demonstrated.…”

Temporal and spatial expression of terpene synthase genes associated with agarwood formation in Aquilaria malaccensis Lam

“…White bars represent samples collected from wounded area (S1) while black bars represent samples collected 5 cm below the wounded area (S2) and ethylene, which play known functions in the cross-talk events among organelles and cells under physiological and stress conditions (Zhao et al 2005;Vasconsuelo and Boland 2007;Hou et al 2013). Agarwood formation at the early phase indeed involves wound signalling transduction process through the activation of several transcription factors, such as MYB4, MYC, WRKY4, EIN3, ERF and bZip, which are commonly involved in stress responses (Xu et al 2003). Agarwood sesquiterpene is a typical inducible secondary metabolite; mechanical wounding and chemical treatment are known to induce sesquiterpene substance production.…”

“…In Aquilaria, guaiene synthesis has been shown to follow the general terpene synthesis pathway established in higher plants, i.e. the cytosolic mevalonic acid (MVA) pathway (Xu et al 2003). From the building precursor isoprenoid, subsequent enzymatic reactions take place, converting the precursor into several intermediates.…”