Differential transcriptome analysis of glandular and filamentous trichomes in Artemisia annua

Abstract

BackgroundThe medicinal plant Artemisia annua is covered with filamentous trichomes and glandular, artemisinin producing trichomes. A high artemisinin supply is needed at a reduced cost for treating malaria. Artemisinin production in bioreactors can be facilitated if a better insight is obtained in the biosynthesis of artemisinin and other metabolites. Therefore, metabolic activities of glandular and filamentous trichomes were investigated at the transcriptome level.ResultsBy laser pressure catapulting, glandular and filamentous trichomes as well as apical and sub-apical cells from glandular trichomes were collected and their transcriptome was sequenced using Illumina RNA-Seq. A de novo transcriptome was assembled (Trinity) and studied with a differential expression analysis (edgeR).A comparison of the transcriptome from glandular and filamentous trichomes shows that MEP, MVA, most terpene and lipid biosynthesis pathways are significantly upregulated in glandular trichomes. Conversely, some transcripts coding for specific sesquiterpenoid and triterpenoid enzymes such as 8-epi-cedrol synthase and an uncharacterized oxidosqualene cyclase were significantly upregulated in filamentous trichomes. All known artemisinin biosynthesis genes are upregulated in glandular trichomes and were detected in both the apical and sub-apical cells of the glandular trichomes. No significant differential expression could be observed between the apical and sub-apical cells.ConclusionsOur results underscore the vast metabolic capacities of A. annua glandular trichomes but nonetheless point to the existence of specific terpene metabolic pathways in the filamentous trichomes. Candidate genes that might be involved in artemisinin biosynthesis are proposed based on their putative function and their differential expression level.

OSC2 and CYP716A14v2 Catalyze the Biosynthesis of Triterpenoids for the Cuticle of Aerial Organs of Artemisia annua

“…In our trichome-specific transcriptome data set reported by Soetaert et al (2013), A. annua BAS was represented by the contig comp33386, which was expressed 72-fold higher (though not significantly, P = 0.192) in the filamentous trichomes compared with the glandular trichomes. (A) Overview of glandular and filamentous trichomes on the A. annua leaf surface.…”

“…A comparative transcriptome analysis of the glandular and filamentous trichomes from the flower buds of the A. annua Anamed A3 cultivar revealed differential expression of terpene biosynthesis genes with triterpene-related contigs being overrepresented in the filamentous trichomes (Soetaert et al, 2013). Comp7642 is one such higher expressed contig that corresponds to an uncharacterized oxidosqualene cyclase (OSC) that we annotated as OSC2.…”

“…The cuticle of the six secretory cells forms a subcuticular sac on the top of the trichome and is thought to function as a storage compartment for secondary metabolites (Olsson et al, 2009). The filamentous trichomes, on the other hand, are made up of five cells that are arranged in a T-shape, of which the top is formed by one elongated cell and the remaining four cells form the stalk ( Figure 1A) (Soetaert et al, 2013). The filamentous trichomes are assumed to function as physical barriers to herbivores and have until now not been explored for their metabolic capacities.…”

“…The filamentous trichomes have not hitherto been investigated for their biosynthetic potential. A recent comparative transcriptome analysis has revealed potentially distinct biosynthetic capacities for the glandular and filamentous trichomes of A. annua (Soetaert et al, 2013). Filamentous trichomes were shown to be enriched in transcripts pertaining to triterpenoid and some specific, nonartemisinin, sesquiterpenoid biosynthesis genes.…”

An ecological implication of glandular trichome-sequestered artemisinin: as a sink of biotic/abiotic stress-triggered singlet oxygen

“…The transcriptome profiling of glandular trichomes from A. annua showed that artemisinin biosynthesis genes are significantly upregulated in both the apical and sub-apical cells of glandular trichomes in A. annua (Soetaert et al 2013). Interestingly, it was observed that water deficit stress induces a decrease in the density and size of glandular trichomes, thereby negatively modulating artemisinin and its precursors (Yadav 2014).…”