Localization of a defensive volatile 4-hydroxy-4-methylpentan-2-one in the capitate glandular trichomes of Oenothera glazioviana

Glandular trichomes of plants produce a wide variety of secondary metabolites which are considered as major defensive chemicals. The capitate glandular trichomes of Oenothera glazioviana(Onagraceae) were collected with laser microdissection and analyzed by gas chromatography-mass spectrometry. The volatile compound 4-hydroxy-4-methylpentan-2-one(1) was identified. We found that compound 1 displays antimicrobial, insecticidal, and phytotoxic activities. These results suggest that compound 1 might function as a defensive compound in the capitate glandular trichomes of O. glazioviana against pathogens, insect herbivores, and presumably competitive plants as well.

Characterization of the Formation of Branched Short-Chain Fatty Acid：CoAs for Bitter Acid Biosynthesis in Hop Glandular Trichomes

Bitter acids, known for their use as beer flavoring and for their diverse biological activities, are predominantly formed in hop （Humulus lupulus） glandular trichomes. Branched short-chain acyI-CoAs （e.g. isobutyryI-CoA, isovaleryl- CoA and 2-methylbutyryI-CoA）, derived from the degradation of branched-chain amino acids （BCAAs）, are essential building blocks for the biosynthesis of bitter acids in hops. However, little is known regarding what components are needed to produce and maintain the pool of branched short-chain acyI-CoAs in hop trichomes. Here, we present several lines of evidence that both CoA ligases and thioesterases are likely involved in bitter acid biosynthesis. Recombinant HICCL2 （carboxyl CoA ligase） protein had high specific activity for isovaleric acid as a substrate （Kcat/Km = 4100 s-~ M-l）, whereas recombinant HICCL4 specifically utilized isobutyric acid （Kcat/Km = 1800 s-1 M-1） and 2-methylbutyric acid （Kcat/ Km = 6900 s-1 M-~） as substrates. Both HICCLs, like hop valerophenone synthase （HIVPS）, were expressed strongly in glandular trichomes and localized to the cytoplasm. Co-expression of HICCL2 and HICCL4 with HIVPS in yeast led to significant production of acylphloroglucinols （the direct precursors for bitter acid biosynthesis）, which further confirmed the biochemical function of these two HICCLs in vivo. Functional identification of a thioesterase that catalyzed the reverse reaction of CCLs in mitochondria, together with the comprehensive analysis of genes involved BCAA catabolism, supported the idea that cytosolic CoA ligases are required for linking BCAA degradation and bitter acid biosynthesis in glandular trichomes. The evolution and other possible physiological roles of branched short-chain fatty acid：CoA ligases in planta are also discussed.

Peltate glandular trichomes of Colquhounia seguinii harbor new defensive clerodane diterpenoids

Glandular trichomes produce a wide variety of secondary metabolites that are considered as major defensive chemicals against herbivore attack.The morphology and secondary metabolites of the peltate glandular trichomes of a lianoid Labiatae,Colquhounia seguinii Vaniot,were investigated.Three new clerodane diterpenoids,seguiniilactones A-C（1-3）,were identified through precise trichome collection with laser microdissection,metabolic analysis with ultra performance liquid chromatography-tandem mass spectrometer,target compound isolation with classical phytochemical techniques,structure elucidation with spectroscopic methods.All compounds showed significant antifeedant activity against a generalist plant-feeding insect Spodoptera exigua.Seguiniilactone A（1） was approximately 17-fold more potent than the commercial neem oil.a-Substituted α,β-unsaturated γ-lactone functionality was found to be crucial for strong antifeedant activity of this class of compounds.Quantitative results indicated that the levels of these compounds in the peltate glandular trichomes and leaves were sufficiently high to deter the feeding by generalist insects.Moderate antifungal activity was observed for seguiniilactone C（3） against six predominant fungal species isolated from the diseased leaves of C seguinii,while seguiniilactones A and B were generally inactive.These findings suggested that seguiniilactones A-C might be specialized secondary metabolites in peltate glandular trichomes for the plant defense against insect herbivores and pathogens.

Characterization of a Cotton Fiber Gene Promoter

Cotton fibers are unicellular trichomes derived from outer integument cells of the ovule.Our previously study showed that cotton R2R3 MYB transcript factor GaMYB2 could complement the Arabidopsis trichome mutant of glabra1(gl1),suggesting that cotton fiber initiation and Arabidopsis

An Artemisia WD40-Repeat Gene Regulates Multiple Cellular Functions in Arabidopsis

In this study, we isolated a WD40-repeat gene from Artemisia annua glandular trichomes. This gene shows 69.97% sequence similarity to Arabidopsis TTG1 at aminoacid level. Sub-cellular localization study shows that AaWD40 protein diffuses in both cell nucleus and cytosol. The correct nuclear localization of AaWD40 was observed when co-expressed with AabHLH, a putative A. thaliana AtTTG1 homologue cloned from Artemisia annua glandular trichomes. When AaWD40 gene was ectopically over expressed in Arabidopsis transparent testa glabrous1-1 (ttg1-1) mutants of A. thaliana, PAs production in seeds was restored, and the trichomeless phenotypes of mutant were rescued. Real-time PCR analysis results revealed that ETC1, CPC, TTG2 and BAN (the downstream targets of AtTTG1 depend on regulatory complex), which regulate the epidermal differentiation and anthocyanin biosynthesis were differentially expressed as a result of AaWD40 over expression. Furthermore, the CLV1, CLV2, CLV3 and WUS, which are required to maintain the stem-cell niche of Arabidopsis shoot apex, were also modulated by AaWD40 and Arabidopsis TTG1. The transcriptions of AP2/ERF, bHLH, MYB, WRKY and NACs family proteins, which are mostly involved in defense, stress response and development regulation, were remarkably modulated by AaWD40 over expression. We hypothesize that WD40 repeat proteins act as a crucial factor in regulating a wide variety of cellular functions in A. thaliana.

Chromosome-level assembly and analysis of the Thymus genome provide insights into glandular secretory trichome formation and monoterpenoid biosynthesis in thyme

Thyme has medicinal and aromatic value because of its potent antimicrobial and antioxidant properties.However,the absence of a fully sequenced thyme genome limits functional genomic studies of Chinese native thymes.Thymus quinquecostatus Celak.,which contains large amounts of bioactive monoterpenes suchas thymol and carvacrol,is an important wild medicinal and aromatic plant in China.Monoterpenoids are abundant in glandular secretory trichomes.Here,high-fidelity and chromatin conformation capture technologies were used to assemble and annotate the T.quinquecostatus genome at the chromosome level.The 13 chromosomes of T.quinquecostatus had a total length of 528.66 Mb,a contig N50 of 8.06 Mb,and a BUSCO score of 97.34%.We found that T.quinquecostatus had experienced two whole-genome duplications,with the most recent event occurring4.34 million years ago.Deep analyses of the genome,in conjunction with comparative genomic,phylogenetic,transcriptomic,and metabonomic studies,uncovered many regulatory factors and genes related to monoterpenoids and glandular secretory trichome development.Genes encoding terpene synthase(TPS),cytochrome P450 monooxygenases(CYPs),short-chain dehydrogenase/reductase(SDR),R2R3-MYB,and homeodomain-leucine zipper(HD-ZIP)IV were among those present in the T.quinquecostatus genome.Notably,Tq02G002290.1(TqTPS1)was shown to encode the terpene synthase responsible for catalyzing production of the main monoterpene product g-terpinene from geranyl diphosphate(GPP).Our study provides significant insight into the mechanisms of glandular secretory trichome formation and monoterpenoid biosynthesis in thyme.This work will facilitate the development of molecular breeding tools to enhance the production of bioactive secondary metabolites in Lamiaceae.