No abstract

Several members of the genus Lavandula produce valuable essential oils (EOs) that are primarily constituted of the low molecular weight isoprenoids, particularly monoterpenes. We isolated over 8,000 ESTs from the glandular trichomes of L. x intermedia flowers (where bulk of the EO is synthesized) to facilitate the discovery of genes that control the biosynthesis of EO constituents. The expression profile of these ESTs in L. x intermedia and its parents L. angustifolia and L. latifolia was established using microarrays. The resulting data highlighted a differentially expressed, previously uncharacterized cDNA with strong homology to known 1,8-cineole synthase (CINS) genes. The ORF, excluding the transit peptide, of this cDNA was expressed in E. coli, purified by Ni-NTA agarose affinity chromatography and functionally characterized in vitro. The ca. 63 kDa bacterially produced recombinant protein, designated L. x intermedia CINS (LiCINS), converted geranyl diphosphate (the linear monoterpene precursor) primarily to 1,8-cineole with K ( m ) and k ( cat ) values of 5.75 μM and 8.8 × 10(-3) s(-1), respectively. The genomic DNA of CINS in the studied Lavandula species had identical exon-intron architecture and coding sequences, except for a single polymorphic nucleotide in the L. angustifolia ortholog which did not alter protein function. Additional nucleotide variations restricted to L. angustifolia introns were also observed, suggesting that LiCINS was most likely inherited from L. latifolia. The LiCINS mRNA levels paralleled the 1,8-cineole content in mature flowers of the three lavender species, and in developmental stages of L. x intermedia inflorescence indicating that the production of 1,8 cineole in Lavandula is most likely controlled through transcriptional regulation of LiCINS.

Background: Lavandula accumulate irregular monoterpenes of unknown biosynthetic origin. Results: We cloned a cis-prenyl diphosphate synthase (cis-PDPS) that produces precursor for irregular monoterpenes in lavenders. Conclusion: Unlike other plants that utilize trans-PDPSs, Lavandula employ a cis-PDPS to initiate the biosynthesis of irregular monoterpenes. Significance: This is the first report of the involvement of a cis-PDPS in irregular monoterpene biosynthesis.

En route to building genomics resources for Lavandula, we have obtained over 14,000 ESTs for leaves and flowers of L. angustifolia, a major essential oil crop, and identified a number of previously uncharacterized terpene synthase (TPS) genes. Here we report the cloning, expression in E. coli, and functional characterization of β-phellandrene synthase, LaβPHLS. The ORF--excluding the transit peptide--for this gene encoded a 62.3 kDa protein that contained all conserved motifs present in plant TPSs. Expression in bacteria resulted in the production of a soluble protein that was purified by Ni-NTA agarose affinity chromatography. While the recombinant LaβPHLS did not utilize FPP as a substrate, it converted GPP (the preferred substrate) and NPP into β-phellandrene as the major product, with K (m) and k (cat) of 6.55 μM and 1.75 × 10(-2) s(-1), respectively, for GPP. The LaβPHLS transcripts were highly abundant in young leaves where β-phellandrene is produced, but were barely detectable in flowers and older leaves, where β-phellandrene is not synthesized in significant quantities. This data indicate that β-phellandrene biosynthesis is transcriptionally and developmentally regulated. We also cloned and expressed in E. coli a second TPS-like protein, LaTPS-I, that lacks an internal stretch of 73 amino acids, including the signature DDxxD divalent metal binding motif, compared to other plant TPSs. The recombinant LaTPS-I did not produce detectable products in vitro when assayed with GPP, NPP or FPP as substrates. The lack of activity is most likely due to the absence of catalytically important amino acid residues within the missing region.

The mycoparasite Clonostachys rosea ACM941 is under development as a biocontrol organism against Fusarium graminearum, the causative agent of Fusarium head blight in cereals. To identify molecular factors associated with this interaction, the transcriptomic and exometabolomic profiles of C. rosea and F. graminearum GZ3639 were compared during coculture. Prior to physical contact, the antagonistic activity of C. rosea correlated with a response heavily dominated by upregulation of polyketide synthase gene clusters, consistent with the detected accumulation of corresponding secondary metabolite products. Similarly, prior to contact, trichothecene gene clusters were upregulated in F. graminearum, while those responsible for fusarielin and fusarin biosynthesis were downregulated, correlating with an accumulation of trichothecene products in the interaction zone over time. A concomitant increase in 15-acetyl deoxynivalenol-3-glucoside in the interaction zone was also detected, with C. rosea established as the source of this detoxified mycotoxin. After hyphal contact, C. rosea was found to predominantly transcribe genes encoding cell wall–degradation enzymes, major facilitator superfamily sugar transporters, anion:cation symporters, as well as alternative carbon source utilization pathways, together indicative of a transition to necrotropism at this stage. F. graminearum notably activated the transcription of phosphate starvation pathway signature genes at this time. Overall, a number of signature molecular mechanisms likely contributing to antagonistic activity by C. rosea against F. graminearum, as well as its mycotoxin tolerance, are identified in this report, yielding several new testable hypotheses toward understanding the basis of C. rosea as a biocontrol agent for continued agronomic development and application.

Several varieties of Lavandula x intermedia (lavandins) are cultivated for their essential oils (EOs) for use in cosmetic, hygiene and personal care products. These EOs are mainly constituted of monoterpenes including camphor, which contributes an off odor reducing the olfactory appeal of the oil. We have recently constructed a cDNA library from the glandular trichomes (the sites of EO synthesis) of L. x intermedia plants. Here, we describe the cloning of a borneol dehydrogenase cDNA (LiBDH) from this library. The 780 bp open reading frame of the cDNA encoded a 259 amino acid short chain alcohol dehydrogenase with a predicted molecular mass of ca. 27.5 kDa. The recombinant LiBDH was expressed in Escherichia coli, purified by Ni-NTA agarose affinity chromatography, and functionally characterized in vitro. The bacterially produced enzyme specifically converted borneol to camphor as the only product with K(m) and k(cat) values of 53 μM and 4.0 × 10(-4) s(-1), respectively. The LiBDH transcripts were specifically expressed in glandular trichomes of mature flowers indicating that like other Lavandula monoterpene synthases the expression of this gene is regulated in a tissue-specific manner. The cloning of LiBDH has far reaching implications in improving the quality of Lavandula EOs through metabolic engineering.

Clonostachys rosea strain ACM941 is a fungal bio-control agent patented against the causative agent of Fusarium Head Blight, Fusarium graminearum. Although the molecular details remain enigmatic, previous studies have suggested that C. rosea may secrete F. graminearum growth inhibitors. Further toward this, experiments described herein show that induction of C. rosea cultures by the addition of an aliquot of F. graminearum(Fg)-spent media (including macroconidia), yield C. rosea (Cr)-spent media that elicited higher anti-F. graminearum activity than either control or deoxynivalenol (DON)-induced Cr-spent media. To gain additional insight into the genetic and metabolic factors modulating this interaction, transcriptomic (RNAseq) profiles of C. rosea in response to DON and Fg-spent media treatment, were developed. This analysis revealed 24,112 C. rosea unigenes, of which 5,605 and 6,285 were differentially regulated by DON and F-spent media, respectively. More than half of these unigenes were up-regulated, with annotations, most notably in the Fg-spent media treatment data, suggesting enhancement of polyketide (PK) and non-ribosomal peptide (NRP) secondary metabolite precursor synthesis, and PK/NRP-like synthases. Four ABC transporters were also up-regulated in response to Fg-spent media. Further analysis showed that the PK and NRP-like synthases belong to three gene clusters that also include ABC transporters, and other genes known to tailor secondary metabolite biosynthesis. The RNAseq data was further validated using quantitative RT-qPCR. Taken together, these results show that C. rosea responds to the presence of Fg-spent media (and to a lesser extent, DON-alone) by up-regulating unique aspects of its secondary metabolism-related genetic repertoire. The identities and roles of C. rosea secondary metabolites produced by the targeted gene clusters are now under investigation.

We identified and characterized EST-SSRs with strong discrimination power against Lavandula angustifolia and Lavandula x intermedia . The markers also showed considerable cross-species transferability rate into six related Lavandula species. Lavenders (Lavandula) are important economical crops grown around the globe for essential oil production. In an attempt to develop genetic markers for these plants, we analyzed over 13,000 unigenes developed from L. angustifolia and L. x intermedia EST databases, and identified 3,459 simple sequence repeats (SSR), which were dominated by trinucleotides (41.2 %) and dinucleotides (31.45 %). Approximately, 19 % of the unigenes contained at least one SSR marker, over 60 % of which were localized in the UTRs. Only 252 EST-SSRs were 18 bp or longer from which 31 loci were validated, and 24 amplified discrete fragments with 85 % polymorphism in L. x intermedia and L. angustifolia. The average number of alleles in L. x intermedia and L. angustifolia were 3.42 and 3.71 per marker with average PIC values of 0.47 and 0.52, respectively. These values suggest a moderate to strong level of informativeness for the markers, with some loci producing unique fingerprints. The cross-species transferability rate of the markers ranges 50-100 % across eight species. The utility of these markers was assessed in eight Lavandula species and 15 L. angustifolia and L. x intermedia cultivars, and the dendrogram deduced from their similarity indexes successfully delineated the species into their respective sections and the cultivars into their respective species. These markers have potential for application in fingerprinting, diversity studies and marker-assisted breeding of Lavandula.