Identification and functional characterization of three type III polyketide synthases from Aquilaria sinensis calli.

Type III polyketide synthases (PKSs) play an important role in biosynthesis of various plant secondary metabolites and plant adaptation to environmental stresses. Aquilaria sinensis (A. sinensis) is the main plant species for production of agarwood, little is known about its PKS family. In this study, AsCHS1 and two new type III PKSs, AsPKS1 and AsPKS2, were isolated and characterized in A. sinensis calli. The comparative sequence and phylogenetic analysis indicated that AsPKS1 and AsPKS2 belonged to non-CHS group different from AsCHS1. The recombinant AsPKS1 and AsPKS2 produced the lactone-type products, suggesting their different enzyme activities from AsCHS1. Three PKS genes had a tissues-specific pattern in A. sinensis. Moreover, we examined the expression profiles of three PKS genes in calli under different abiotic stresses and hormone treatments. AsCHS1 transcript was most significantly induced by salt stress, AsPKS1 abundance was most remarkably enhanced by CdCl2 treatment, while AsPKS2 expression was most significantly induced by mannitol treatment. Furthermore, AsCHS1, AsPKS1 and AsPKS2 expression was enhanced upon gibberellins (GA3), methyl jasmonate (MeJA), or salicylic acid (SA) treatment, while three PKS genes displayed low transcript levels at the early stage under abscisic acid (ABA) treatment. In addition, three GFP:PKSs fusion proteins were localized in the cytoplasm and cell wall in Nicotiana benthamiana cells. These results indicated the multifunctional role of three type III PKSs in polyketide biosynthesis, plant resistance to abiotic stresses and signal transduction.

Five 2-(2-Phenylethyl)chromones from Sodium Chloride-Elicited Aquilaria sinensis Cell Suspension Cultures.

Five 2-(2-phenylethyl)chromones including a new one, (5S,6R,7S,8R)-5,8-dichloro-6,7-dihydroxy-2-phenylethyl-5,6,7,8-tetrahydro-4H-chromen-4-one (1), and four known ones (2-5), were isolated from 150 mM NaCl-elicited Aquilaria sinensis cell suspension cultures. In addition, three feruloyl amides (6-8), six nucleosides (9-14), (+)-syringaresinol (15), indole-3-carboxaldehyde (16), and two glycosides (17-18) were also obtained. The structures were unambiguously identified by analysis of their UV, IR, NMR, and HRESIMS data. The absolute configuration of the new 2-(2-phenylethyl)chromone (1) was established by a dimolybdenum tetraacetate-induced circular dichroism experiment. Compared to un-elicited cell lines, the appearance of 2-(2-phenylethyl)chromones in NaCl-treated cells occurred on the 3rd and 5th days of their treatment. 2-(2-Phenylethyl)chromones, feruloyl amides, nucleosides, and lignins have been reported to be closely related to plant defense; therefore, the identification of these compounds from NaCl-elicited A. sinensis cell suspension cultures would be useful for further exploring the mechanism of agarwood formation.

[Establishment of a cell suspension culture system of endangered Aquilaria sinensis (Lour.) Gilg].

Aquilaria sinensis callus induced by stem tips were used to establish the suspension cell system. The results showed that the most suitable medium for callus induction and subculture is MS + 2.0 mg x L(-1) NAA + 1.0 mg x L(-1) 6-BA. After 12 times of subculture, the energetic and loose callus, which were appropriate for cell suspension culture, were cultured and shook in liquid medium MS + 2.0 mg x L(-1) NAA + 1.0 mg x L(-1) 6-BA + 500.0 mg x L(-1) casein hydrolysate (CH) to establish the suspension cell system. The growth curve of suspension cells showed a "S" type. At the beginning of the culture, cell density increased slowly; during 4 to 6 days, suspension cells reached logarithmic growth period; during 7 to 12 days, suspension cells were in the platform period; but after 12 days, cell density and activity went down obviously. Agarwood sesquiterpenes were not detected in the suspension cells during the growth period, however, they could be detected in MeJA treated suspension cells. In this study, a stable and active growing suspension cell system was established, which was a proper system to study the mechanism of agarwood sesquiterpene formation, and additionally provided a potential way to generate agarwood sesquiterpenes through application of cell culture.

Neolignans and sesquiterpenes from cell cultures of Stellera chamaejasme.

Two new neolignans (1, 2) and six sesquiterpenes (3- 8) were isolated from the cell cultures of Stellera chamaejasme. Their structures and absolute configurations were elucidated by extensive spectroscopic and computational methods. Compound 4 exhibited significant protective effects against CCl (4)-induced hepatotoxicity in HepG2 cells, reducing aspartate aminotransferase release by 29.49 % at 10 µM. These compounds have not been isolated from plant material, which implies that in vitro plant cell cultures may offer alternative and effective sources of bioactive natural compounds.

Characterization of delta-guaiene synthases from cultured cells of Aquilaria, responsible for the formation of the sesquiterpenes in agarwood.

The resinous portions of Aquilaria plants, called agarwood, have been used as medicines and incenses. Agarwood contains a great variety of sesquiterpenes, and a study using cultured cells of Aquilaria showed the production of sesquiterpenes (α-guaiene, α-humulene, and δ-guaiene) to be induced by treatment with methyl jasmonate (MJ). In this study, the accumulation and production of sesquiterpenes were quantified. The amounts accumulated and produced reached a maximum at 12 h, and the most abundant product was α-humulene at 6 h and δ-guaiene after 12 h. However, a headspace analysis of the cells revealed that α-humulene is likely to be volatilized; so overall, the most abundant sesquiterpene in the cells was δ-guaiene. A cDNA library from RNA isolated from MJ-treated cells was screened using PCR methodologies to isolate five clones with very similar amino acid sequences. These clones were expressed in Escherichia coli, and enzymatic reactions using farnesyl pyrophosphate revealed that three of the clones yielded the same compounds as extracted from MJ-treated cells, the major product being δ-guaiene. These genes and their encoded enzymes are the first sesquiterpene synthases yielding guaiane-type sesquiterpenes as their major products to be reported. Expression of a fourth terpene synthase gene in bacteria resulted in the accumulation of the protein in insoluble forms. Site-directed mutagenesis of the inactive clone and three-dimensional homology modeling suggested that the structure of the N-terminal domain was important in facilitating proper folding of the protein to form a catalytically active structure.

[Study on karyotype and giemsa C-banding of Aquilaria sinensis].

OBJECTIVE: To study Aquilaria sinensis (Lour.) Spreng chromosome karyotype and C-banding. METHOD: Sections for karvotvpe and BSG method for C-banding. RESULTS: The somatic chromosome number was 2n=16, karyotype formula was K(2n) = 2x = 16 = 6m + 6sm + 4st, based on Levan's publication in 1964. According to the method of Kuo, the chromosome based on the relative length was 2n = 16 = 4L + 4M2 + 6M1 + 2S, which belonged to "2B". 8 pairs chromosomes had 34 C-bands and the C-banding patter was 2n = 2x = 16 = 4C + 2I + 2T + 2CI+ + 2CI+ T + 2CI+ T+ + 2I+ T+. CONCLUSION: The data of karyotype and C-banding indicated A. sinensis chromosome had a relatively high asymmetry and was in the advanced stage of evolution, which offered the evidence for further genetic analysis.